Autonomous current charging of dry-cooled superconducting MR electromagnetic coil systems

Abstract

The invention relates to a method for operating a magnetic resonance (= "MR") device (10) without a refrigerant, superconductive MR solenoid system (12), said method being characterized by comprising the following steps in order to autonomously charge the superconductive MR solenoid system: (a1) starting a cooling process of the coil system; (a2) starting an automatic current charging program; (b1) measuring a current temperature Tcoil on the coil system and comparing the Tcoil with a first temperature setting value T1ramp which can be specified, from which the coil system is superconductive and is to be charged; (b2) if Tcoil < = T1ramp: supplying a charging current into the coil system and charging the coil system with a current; (c) measuring the current Icoil which is currently flowing in the coil system and comparing the Icoil with a first current setpoint I1target which can be specified at which the coil system produces the desired magnetic field strength; (d) repeating the steps (b1), (b2) and (c) until Icoil is equal to I1target; (e) turning off the supply of current into the coil system (12) and stopping the automatic current charging procedure. As a result, the electromagnetic coil system can be charged autonomously with an electric current.

Description

Technical Field

[0001] The invention relates to a method for operating a magnetic resonance (MR) system having a superconducting MR electromagnetic coil system which is arranged in a vacuum vessel and which is dry (refrigerant-free) in MR measuring operation, and having a cryostat for cooling the MR electromagnetic coil system, the cryostat comprising a neck tube which leads through the housing of the vacuum vessel to the MR electromagnetic coil system, wherein cooling arms of a cold head are at least partially arranged in the neck tube and cool the superconducting MR electromagnetic coil system to a superconducting temperature and then supply it with a charging current. Background Art

[0002] Such a method and the associated MR system are known from DE 10 201 6 218 000 B3 (=reference [1]).

[0003] The invention relates generally to the field of current charging of superconducting magnet arrangements which should / must be kept at very low (= cryogenic) temperatures during operation. Such superconducting magnet arrangements are used in the field of magnetic resonance, for example MRI (= magnetic resonance imaging) tomographs or NMR (= nuclear magnetic resonance) spectrometers.

[0004] Nuclear magnetic resonance is a high-performance instrumental analysis method, with which the chemical composition of a measurement sample can be determined in particular. Here, high-frequency pulses are irradiated into the measurement sample in a strong static magnetic field, and the electromagnetic response of the sample is measured. The strong static magnetic field, which is particularly uniform in nuclear magnetic resonance, is often generated by superconducting magnet systems, which for this purpose usually have to be cooled to extremely low cryogenic temperatures close to absolute zero during measurement operation using liquid helium as a cryogenic fluid.

[0005] Such superconducting magnet systems are usually also equipped with active cooling. In this case, the systems usually no longer have a fluid tank in which the magnet is directly surrounded by a cryogenic fluid. Instead, the coils of the magnet system are arranged in a vacuum vessel and are therefore "dry", i.e., cryogen-free, in the MR measurement operation. Usually, the radiation shield surrounding the vacuum vessel, but sometimes also the magnet system, is cooled directly by an active cooler, for example a pulse tube refrigerator or a Gifford-McMahon refrigerator.

[0006] These dry systems are usually prone to cooling system failures, for example when the cold head fails, because, unlike bath-cooled magnet systems, there is no temperature buffer in the form of a usually liquid refrigerant directly surrounding the magnet system, which can evaporate in the event of a cooling system failure and thus maintain cryogenic temperatures for a longer period of time. In contrast, such bath-cooled systems require greater labor expenditure and higher costs during commissioning, because large amounts (up to several thousand liters) of liquid helium and nitrogen are used for cooling and filling, which must be refilled in the event of a quench. Therefore, bath-cooled systems cannot be operated self-sufficiently.

[0007] The use of an active cooling system reduces the consumption of expensive liquid helium, increases the availability of the NMR system, and can also contribute to reducing the size of the structure. The active cooling system can be constructed as a single stage or also as a multi-stage system. In a multi-stage system, the hotter cooling stage usually cools the thermal radiation shield, while the colder cooling stage cools the object to be cooled.

[0008] US 8 729 894 B2 (=reference [2]) discloses a magnet system for MRI, comprising a container with a liquid refrigerant therein and a superconducting magnet inside the container, the container being configured such that it can be removably connected to a vacuum pump, the vacuum pump in turn being configured such that the vacuum pump pumps the refrigerant out of the container in order to reduce the pressure level in the container to a pump low pressure level during startup of the superconducting magnet and to increase the pressure level from the pump low pressure level to a normal operating pressure level during normal magnet operation in order to increase the pressure level. Reference [2] also describes a method for charging the magnet, in which the container with the magnet can be emptied during so-called ramping. The cold head is arranged in the neck tube without affecting the vacuum in the container. However, the cryostat contains liquid helium. Reference [2] constitutes a significantly different prior art for the present invention, since it is a "wet-cooled" coil system, in which self-sufficient operation is not possible.

[0009] US2005 / 0111159 A1 (=reference [3]) describes an MRI device having a superconducting magnet, which is also helium-bath cooled, as in reference [2], and includes a technology for automatically applying a current to the magnet, with automatic control of a "ramp-up" based on a predetermined value of a target parameter (magnetic field strength, current strength or magnet temperature). The so-called "autoramp controller" controls the charging while taking into account the measured parameters, in particular the temperature. In this case, reference [3] discloses a method for automatically starting operation of a superconducting magnet. Here, the operating value of a limiting parameter should be measured and compared with the set value of the limiting parameter in order to control the current supply. During the startup, the startup rate can be controlled in amperes per minute depending on the magnet current and the magnet temperature. The autoramp controller can gradually increase the current until a determined magnet current is reached. At the same time, the magnet temperature should be prevented from exceeding a predetermined value.

[0010] However, reference [3] does not describe how this can be achieved. In particular, reference [3] does not disclose a specific charging algorithm, such as the algorithm necessary for charging very sensitive superconductors that are not stored in a cooling bath and by which the hysteresis heat generated during charging is ensured to be removed. It is only described in very general terms that a control unit monitors the start-up by measuring various parameters (T and I). There is no provision for interrupting the charging if the magnet temperature is too high. The autoramp controller divides the charging process into two main phases, namely a first, fast charging phase and a slower, second charging phase, in which current is already present in the coil and a quench is therefore very likely to occur.

[0011] DE 10 201 4 218 773 B4 (=reference [4]) discloses that in a cryostat, the hollow volume between the inside of the neck tube and the cooling arms of the cold head is filled with a gas, for example helium. In normal operation, the lowermost cooling stage of the cooling arm is in the vicinity of the object to be cooled; for example, a close thermal coupling is established by the contact of the object to be cooled and the lowermost cooling stage with a small amount of liquid helium in the hollow volume. In the event of a cooling failure, the gas pressure in the hollow volume increases due to the temperature increase; any liquid helium in the hollow volume evaporates. The movably mounted cold head moves in a direction away from the object to be cooled due to the increased gas pressure in the hollow volume, whereby the thermal coupling between the cooling arms and the object to be cooled is reduced. With such a cryostat, the thermal load can be reduced by means of the cooling arms in the event of a failure of active cooling, but the structural complexity is high due to the movable suspension of the cold head. In addition, a significant thermal coupling still exists due to the high gas pressure in the hollow volume.

[0012] DE 10 201 5 215 919 B4 (=reference [5]) describes a method and a device for precooling a cryostat with a heat pipe, such as that shown in reference [4]. During the precooling phase, the object to be cooled is precooled to a target temperature of the operating range of the cryogenic working medium, within which the heat pipe can operate effectively, wherein for precooling, a short-circuit block with good thermal conductivity and precise fit is inserted into the heat pipe through the neck tube, the free end of the short-circuit block being thermally connected to a high-power cooling device, the other end of the short-circuit block being in contact with a thermal contact surface. After reaching the target temperature, the short-circuit block is removed from the heat pipe in an intermediate phase, and then, in the operating phase, heat is transferred via the heat pipe in a condensing operation. As a result, the time required for precooling the cryostat to its operating temperature can be significantly shortened, so that the duration of the startup (Inbetriebnahme) can be significantly shortened.

[0013] US2021 / 0080527 A1 (=reference [6]) describes a magnetic resonance tomography scanner having a superconducting magnet supported in a helium-free cryostat. The magnet is cooled by a heat pipe, which is operated with helium and is connected to a cold head. The magnet system also includes a so-called intelligent monitoring system, which ensures real-time monitoring of the operating state, in particular the temperature (using a T sensor) and an external power supply. The operating control system can take corresponding measures, including controlling the heat conduction component and the superconducting power supply to implement magnet excitation and demagnetization. Autonomous charging is not disclosed in this document.

[0014] Reference [1] cited above describes a cryostat device having a vacuum container and a cooling target arranged in the vacuum container, the vacuum container having a neck tube leading to the cooling target, a cooling arm of a cold head arranged in the neck tube, a closed cavity formed around the cooling arm, the neck tube being sealed against the cooling target fluid and filled with a cryogenic fluid during normal operation. The refrigerant in the neck tube can evaporate under vacuum to achieve cooling and can be pumped out, in particular when the cooling function fails, in order to thermally decouple the cold head from the vacuum container. Such a cryostat can be used to implement a general method having the combination of features defined above. However, in reference [1], there is not even an implicit mention, let alone an explicit description, of charging the electromagnetic coil with an electric current.

[0015] However, a disadvantage of all the related methods known in this context for current charging of dry superconducting MR magnetic coil systems in MR measuring mode, ie not surrounded by a cryogenic medium, is that previously, specialized personnel were always and absolutely required.

[0016] During this operating phase of charging the magnetic coils, which in principle always has to be completed after the system is first installed at the customer's site, but which also has to be completed every time after a temporary heating of the superconducting magnet, for example during a quench, completely autonomous operation of the MR system has hitherto been impossible without the involvement of a highly complex and specially trained service technician.

[0017] That is, the conventional practice in the prior art always includes and only includes manual charging of the MR electromagnetic coil system by maintenance personnel. The charging plan for the magnet is manually set and prepared by the maintenance technician at the power supply. Here, malfunctions may occur due to incorrect operation of the sometimes complex charging plan.

[0018] Furthermore, this charging process also requires a lot of time and can last for several days. This also takes up a corresponding amount of work time for the technicians required on site, since, for safety reasons, manual charging has so far only been carried out during the day. Inadvertence during charging can lead to errors, such as, for example, increased coil temperatures or HTS coupling temperatures. Such errors can lead to quenching or even damage to the HTS current bar.

[0019] DE 10 202 1 206392.6 (=reference [0]), filed by the applicant with the German Patent and Trademark Office on June 22, 2021, which was still confidential at the filing date of the present invention and had not been published before that date, describes an autonomous method for autonomously cooling a cryostat-based NMR device, in particular for MRI, at the customer's site to a temperature at which the magnet can be charged and, if necessary, recharged. The invention of this automatic cooling method itself already makes it unnecessary for maintenance work to be carried out by specialists for this purpose. However, the very complex charging procedure for automatically and also autonomously charging the MR electromagnetic coil system, which is also without the need for active assistance from maintenance personnel, is not even implicitly disclosed in reference [0]. Summary of the invention

[0020] In contrast, the object of the present invention, which is initially demanding and complex in terms of details, is to improve a method for operating an MR system of the type described above, which has a superconducting MR electromagnetic coil system which is arranged in a vacuum vessel “dry” and which is free of refrigerant during MR measurement operation, and a cryostat for cooling the system, and to improve a device for carrying out the method using simple, readily available or usually standardly already available technical means at the user, in such a way that the charging of the superconducting MR electromagnetic coil system with electric current can be carried out completely automatically after start-up (“by pressing a button”) in most cases autonomously and also in a targeted manner with respect to certain process parameters, and this should be carried out in the simplest manner and without the need for external or expensive additional components. In particular, the thermal load caused by the charging process should be reduced and the safety against superconductor quenching should be increased.

[0021] With regard to an operating method for autonomously charging a superconducting MR electromagnetic coil system, the object is achieved by the invention in a surprisingly simple and effective manner by the following steps:

[0022] (a1) starting the cooling process of the superconducting MR electromagnetic coil system;

[0023] (a2) starting an automatic current charging procedure for the superconducting MR electromagnetic coil system;

[0024] (b1) Measure the current temperature T on the MR electromagnetic coil system coil , and T coil The first temperature setting value T1 can be predetermined ramp In contrast, starting from the first temperature setting, the MR electromagnetic coil system is superconducting and should be charged, wherein T1 ramp Usually less than the critical transition temperature T from the normal conducting state to the superconducting state C ;

[0025] (b2) If T coil ≤T1 ramp : supplying a charging current to the MR electromagnetic coil system and charging the MR electromagnetic coil system with the current;

[0026] (c) Measure the current I flowing in the MR electromagnetic coil system coil , and I coil and the first current setting value I1 which can be predetermined target In comparison, the MR electromagnetic coil system generates a desired magnetic field strength at a first current setting;

[0027] (d) Repeat steps (b1), (b2) and (c) until I coil=I1 target ;

[0028] (e) Shutting down the current supply to the MR electromagnetic coil system (12) and stopping the automatic current charging process.

[0029] The automated method according to the invention for charging superconducting magnets in a helium-free cryostat comprises the steps defined above at a predetermined charging voltage and under strict monitoring by sensors but automatically, by running a precise computer program. This process can be significantly more variable, imprecise and error-prone when charging by a technician. This increases the operating safety of the system at all times. This system is monitored by error reports, which can be sent, for example, as e-mails to remotely located monitoring personnel who do not have to be constantly active (e.g. "Attention, gas cylinder charge is running low" etc.). The advantageous result is a significant saving in maintenance personnel and less system downtime.

[0030] In addition, more complex charging processes can be implemented, which may not be possible at all or can only be carried out manually with great effort, such as cooling and charging over several days and nights. As a result, high-value magnet systems and expensive NMR devices usually have to withstand significantly less downtime. By fully monitoring and automatically carrying out the charging, the magnets can also be better utilized in terms of their current carrying capacity. As a result, the magnets can be designed to be more compact and lighter and more economical to produce.

[0031] The control unit controls the different components by means of algorithms taking into account the different measured values ​​and parameters. The control unit also includes an automatic current charging program, for example on an FPGA, which is called up for the charging process.

[0032] An important subordinate aspect is the "button" principle, according to which the magnet can be charged simply by pressing a button.

[0033] But it may even be another object of the invention to provide a completely self-sufficient magnet system which automatically and independently cools to a sufficiently low cryogenic temperature by pressing a button and subsequently generates an NMR magnetic field with the desired magnetic field strength by autonomously charging the MR electromagnetic coil system, without the need for monitoring personnel and operating technicians to be present for this entire complex process.

[0034] Now, by combining the feature combination of the present invention with the processing method disclosed in reference [0], this goal of automatically cooling and charging the superconducting electromagnetic coil can be achieved.

[0035] This results in a novel operating method which, by means of a simple control unit, cools the superconducting magnet system autonomously almost at the push of a button and also automatically charges the magnetic coil with current starting from a suitable cryogenic temperature.

[0036] The system can react accordingly to external disturbances, generate an error report if necessary, and send it to a monitoring center which does not have to be deployed on site. The electromagnetic coil system is essentially self-sufficient and autonomous in this way and can not only operate automatically without further involvement of technicians, but can also be flexibly and simply adjusted to the operating temperature and magnetic field even by the end customer himself.

[0037] The result is a significant saving in maintenance, especially with regard to the use of specialist personnel by the operator of the MR system, and less downtime of the system. The entire system as a whole becomes more compact, lighter and more economical in every respect.

[0038] An MR system for carrying out the method according to the invention described above is equipped with a superconducting MR magnet system which is arranged in a vacuum vessel and which is dry, i.e., refrigerant-free, in MR measuring operation, and with a cryostat for cooling the MR magnet system, the cryostat comprising a neck tube which leads through the housing of the vacuum vessel to the MR magnet system, wherein cooling arms of a cold head are at least partially arranged in the neck tube, around which a closed cavity is formed, which cavity is sealed in a fluid-tight manner with respect to the MR magnet system to be cooled and which is at least partially filled with a cryogenic fluid in normal operation of the MR system.

[0039] For this MR device, the larger inventive object of also autonomous cooling and charging is achieved by means of a substantial combination of features, namely, a vacuum pump is arranged outside the vacuum vessel and a first shut-off valve is arranged in the vacuum line leading from the vacuum pump into the vacuum vessel, and there is a device for measuring the current temperature T at the MR electromagnetic coil system. coil The temperature sensor and the current pressure P in the vacuum container are used to measure ist The first pressure sensor and the control unit are configured to detect the current temperature T of the MR electromagnetic coil system. coil It is compared with the pre-set temperature setting value to detect the current pressure P in the vacuum container. ist The pressure is compared with a predetermined pressure setting value and used to control the first shut-off valve, the vacuum pump, the cold head and the charging power source.

[0040] In combination with the cooling method disclosed in reference [0], a cryostat suitable for implementing the charging method according to the invention described above thus contributes to achieving the expanded inventive object, namely, a fluid conduit is provided, which at one end leads to a cavity of a cooling arm surrounding a cold head and at the other end leads to a pressure vessel filled with a cryogenic fluid outside the neck tube, and there is a pressure vessel for measuring the current pressure P in the cavity. HR The second pressure sensor.

[0041] Finally, the device for implementing the novel method requires an electronic control unit configured to detect the current temperature T on the MR electromagnet coil system. coil It is compared with the pre-set temperature setting value and used to detect the current pressure P in the vacuum container. ist This is compared with a predefined pressure setpoint and the control unit controls the various components by means of algorithms taking into account the various measured values ​​and parameters. The control unit is important for the functionality of the autonomous cooling, since this requires continuous detection of temperature and pressure values ​​and appropriate control of the vacuum pump and the cooling according to the available measured values ​​with the aid of algorithms provided for this purpose.

[0042] The control unit contributes to achieving the object of the invention in that it has a measuring unit for measuring the current temperature T at the MR electromagnetic coil system. coil The temperature sensor and the current pressure P in the vacuum container are used to measure ist The pressure sensor is connected to the measuring unit. The measuring unit preferably also includes a temperature sensor for measuring the current temperature T on the radiation shield of the cryostat. shield In addition, the control unit further comprises a control unit for opening and closing the first shut-off valve, for activating and deactivating the vacuum pump, and for activating and deactivating the cold head, and comprises a processor unit, which is configured as an interface between the measuring unit and the control unit for comparing the detected sensor parameters with the set parameters and for processing data for controlling the cold head, the vacuum pump, the shut-off valve, and the charging power supply.

[0043] Particular advantages of the autonomous cooling and charging method according to the invention:

[0044] 1. Automatic cooling and charging process during the first start-up of an MR system with a superconducting electromagnetic coil system

[0045] 2. Automatic cooling and charging process after failure of the cooling device or after overheating of the quench solenoid system (="automatic cooling")

[0046] 3. Continuous temperature and pressure measurement allows:

[0047] a) Automatically check the current temperature T on the MR electromagnetic coil system coil and T on the radiation shield shield ;

[0048] b) Automatically check the current pressure P in the vacuum container ist .

[0049] Variants, preferred embodiments and improvements of the present invention

[0050] A preferred variant of the method according to the invention has very particular advantages in which the following intermediate step is carried out between step (d) and step (e):

[0051] (d1) Once I coil =I1 target : Stop the cooling process of the superconducting MR electromagnetic coil system (thereby the electromagnetic coil system slowly heats up);

[0052] (d2) Measure the current temperature T on the MR electromagnetic coil system coil , and T coil The second temperature setting value T2 can be predetermined tov <T C In contrast, at the second temperature setting, the superconducting current carrying capacity of the MR electromagnetic coil system is reduced to a predeterminable lower value, without the superconductivity in the electromagnetic coil system completely collapsing;

[0053] (d3) Once T coil =T2 tov : Restarting the cooling process of the superconducting MR electromagnetic coil system.

[0054] In this state, the compressor is shut down and maintained until the coil temperature T coil Reach the set temperature limit value T2 tov , the temperature of the thermal overshoot. Depending on the specific magnet system, this can last up to one hour. Once T2 is reached tov , activate the compressor again and wait for a fixed time, for example about 20 seconds, in order to give the compressor time to start. Thereafter, a switch is made to the operating state, in which the cooling system is activated so that any evaporated helium from the neck tube can be reliquefied. This also occurs in the event of a sensor failure. If the magnet could quench in this state, the temperature T coil rises above a critical value and the charging process must be restarted by bringing the coil temperature back to T in the cryostat coil ≤T1 ramp .

[0055] The thermal overshoot evens out and optimizes the current distribution in the superconducting wire. As a result, the drift specification is reached in a significantly faster time. MR-specific measurements can thus start directly after the thermal overshoot. For conventional magnet systems without thermal overshoot, this can last from one day to several weeks.

[0056] The thermal overshoot is preferably part of the automatic charging process and shortens the time to reach the "drift specification", that is, to stabilize the current in the superconducting coil to such an extent that the magnetic field no longer changes or only changes slightly. In other words, a thermal overshoot ultimately occurs after each charging process. The thermal overshoot serves to force a faster and more uniform current distribution in the superconducting filaments due to the temperature increase, so that the magnet reaches its drift specification more quickly (no recoupling in the filaments).

[0057] In conventional bath-cooled magnet systems, overshoot is achieved by slightly overcharging above the set current intensity and then falling back to the set current intensity. Surprisingly, a simple thermal overshoot has the same effect, i.e. reaching the drift specification in a short time, without changing the current intensity in the coil.

[0058] It is also surprising that this time is drastically reduced, so that the 7T magnet is already within specification after one day, after the thermal overshoot has subsided. Here, in the absence of thermal overshoot, this lasts about four days.

[0059] For 9T magnets, this lasts slightly longer due to the high filaments, and the thermal overshoot is also prolonged because of the more frequent and therefore longer stays in the elevated temperature range. After the thermal overshoot has subsided, the magnet should be within specification after about 2-3 days. Here, without thermal overshoot, this lasts up to a week or more.

[0060] For bath-cooled magnets, the thermal overshoot lasts a long time, since the entire amount of helium must be heated. This is only possible within a limited temperature range.

[0061] The following variants of the method according to the invention may also be advantageous, in which, after reaching the criterion T coil =T2 tov Steps (d1) to (d3) are then repeated several times. Repeating several times accelerates the process. This additionally shortens the time until the drift specification is reached. With each thermal overshoot, this decay behavior can be additionally shortened and, depending on the specific magnet system, the typical drift value can be reached within a few hours.

[0062] In another important variant of the process according to the invention, if in step (b2) T coil >T1ramp , the charging of the MR electromagnetic coil system 12 with current is interrupted, and the cooling process continues until T coil ≤T1 ramp ; Thereafter, the process is resumed with step (b1).

[0063] The thermal load of the charging process is reduced by “parking”. This again increases the thermal load relative to T c temperature margin.

[0064] The stop / interruption of the charging process is normally a transient state and serves to achieve safety against quenching of the superconductor, since heat is generated during the charging process which may not be dissipated quickly enough.

[0065] At the time of the interruption, the target current is first set to the currently measured current and the voltage to 0 V, the main heater and the shield heater are also deactivated, thus short-circuiting the magnet. Thereafter the current is recorded and the main current is set to 0 A and thus drained from the cable. Once the current is at 0 A, only cooling remains active.

[0066] A class of embodiments of the method according to the invention is also particularly preferred, which are characterized in that a closed cavity is formed around the cooling arm, the cavity is sealed fluid-tightly with respect to the MR electromagnetic coil system to be cooled and is at least partially filled with liquid helium during normal operation of the MR system, the neck tube is connected via a first valve V1 to a helium supply device, on the one hand, via which helium can be introduced in order to liquefy it at the cooling arm, and on the other hand, during steps (c) and (d), the helium in the neck tube is pumped out via the helium supply device, the method comprising the following steps:

[0067] (c0') measures the current I currently flowing in the MR electromagnetic coil system (12) coil , and I coil and a second current setting value I2 which can be predetermined pump <I1 target In contrast, starting from the second current setting value, helium in the neck tube (14) should be pumped out; and

[0068] (c0”) Once I coil ≥I2 pump : Activate the vacuum pump arranged outside the vacuum container (11), open the first stop valve (27) in the pump-out pipeline introduced from the vacuum pump into the neck tube, so as to use the vacuum pump to pump helium out of the neck tube.

[0069] By pumping helium out of the neck, lower temperatures can be achieved in the cryostat. On the one hand, this protects the superconductor from heating up during charging and thus speeds up the charging process itself, since there are fewer interruptions.

[0070] This results in an additional cooling power which makes it possible to reach lower temperatures than would be achievable with a cold head alone. c This approach enables the reliable implementation of particularly critical thermal margins designed close to T c Therefore, a smaller and more compact magnet system can be constructed.

[0071] Advantageous are the following refinements of these method variants in which the supply line to the neck is connected to a vacuum pump via a further valve V3 and in step (f) helium is supplied to the neck and liquefied.

[0072] Since the volume of helium that can be pumped is limited to a small amount (e.g. 1.5 liters) of liquid helium, it can only be pumped within a certain time, after which the helium must be liquefied again. Once the pumping time defined in the charging plan is exceeded, the helium must be liquefied.

[0073] This allows the helium that may have been pumped out during charging to be refilled and liquefied. This ensures that, in the event of a cooling unit failure, a complete volume of helium is always available for evaporation. This allows the time until a quench occurs after a cooler failure to be extended to several hours.

[0074] The method variant described can also be alternatively or additionally developed in such a way that, if necessary, for example in the event of a failure of the cold head, in a step (c0'') between steps (c) and (d), if necessary before steps (d1) to (d3), the liquid helium in the neck tube is pumped out by means of a vacuum pump in order to cool the MR electromagnetic coil system.

[0075] This makes it possible to construct a magnet system that has a design temperature below the evaporation temperature of helium (4.2 K). This makes it possible to construct a smaller, more compact magnet system.

[0076] If a cold head failure does occur, this method step serves to prevent a quenching of the superconductor, since the time to warm up to the transition temperature is then prolonged.

[0077] Embodiments of the method according to the invention are also preferred in which, in step (b1), the current temperature T at the radiation shield 55 is additionally measured. istshield , and compare it with the pre-determined temperature setting value T shield Compared with, and if T istshield ≤T shield , then supply charging current according to step (b2).

[0078] This prevents the HTS current bar from reaching its critical temperature during the charging process of the magnet and burning through.

[0079] During the charging process, the current supply to the superconducting magnet takes place via so-called current bars, which contain a good conductor of electricity. For magnets without cryogen, high-temperature superconductors (=HTS) are used, since the heat input into the cryostat is lower with high-temperature superconductors, for example compared to copper. The HTS current bars are usually thermally connected to a radiation shield, which should be at a temperature T below the transition temperature of the HTS conductor. shield The temperature of the radiation shield is therefore monitored so that the HTS conductor does not quench during the charging process and thus be destroyed.

[0080] These method variants can also be improved in that if T istshield >T shield , the charging of the MR electromagnetic coil system with current in step (b2) is interrupted, and the cooling process is continued until T istshield ≤T shield , thereafter resuming the process with step (b1).

[0081] This prevents the HTS current bar from reaching its critical temperature and burning through during the magnet charging process. When the radiation shield temperature reaches a critical range for the HTS conductor, charging should be interrupted to avoid HTS quenching. By "parking" the charging process, the HTS current bar is cooled.

[0082] As already explained above in connection with the autonomous cooling method, a special electronic control unit is required for automatically carrying out the method sequence. The same applies to the autonomous charging method according to the invention. Therefore, a particularly preferred class of embodiments of the method according to the invention is characterized in that the autonomous charging process of the superconducting MR electromagnetic coil system is automatically controlled by means of an electronic control unit, which is configured to detect the current temperature T at the MR electromagnetic coil system. coil Or detect the current temperature T on the radiation shield istshield It is compared with the pre-set temperature setting value and used to detect the current I flowing in the MR electromagnetic coil system. coil This is compared with a predefined current setpoint and used, if necessary, to control valves, charging current sources, vacuum pumps and functional units for controlling the cold head.

[0083] The electronic control unit plays a central role in connection with the charging process, since it includes an automatic current charging program which includes an optimized charging plan for each magnet type, which ensures standardized and safe charging of the magnets. As a result, a highly complex self-monitoring charging process with pauses and variable limit values ​​can be implemented safely and reliably in a temperature-optimized manner, if necessary over a long period of time.

[0084] Advantageous here are the following developments of such method variants in which the electronic control unit autonomously regulates the autonomous charging process of the superconducting MR magnetic coil system by means of an algorithm, taking into account various measured values ​​and parameters such as, for example, pressure, temperature, charging voltage, charging current, even in the absence of an operator or monitoring personnel, during the night, in particular for several days, without interruption in time and fully automatically.

[0085] As a result, highly complex self-monitoring charging processes with pauses and variable limit values ​​can also be carried out safely and reliably in a temperature-optimized manner, if necessary over a long period of time.

[0086] However, these refinements can also be developed in that, during the autonomous charging process of the superconducting MR magnet coil system, the electronic control unit independently detects critical state changes and faults of the superconducting MR magnet coil system and of a cryostat for cooling the MR magnet coil system, in particular detects temperature, current and pressure values ​​in the vacuum vessel, and responds thereto by using predefinable alternative algorithms for further regulating the autonomous charging process and / or by sending a message or fault report, for example an e-mail message, to an operating or monitoring person.

[0087] In this way, intervention can be carried out early if an impending problem or even a magnet quench is foreshadowed. For example, in the event of a cooling water failure, an e-mail can be sent to the facility manager, or in the event of an increase in the hood temperature, for example, an e-mail can be sent to the magnet maintenance department. This significantly reduces possible downtimes and prevents interruptions to MR measurements.

[0088] Alternatively or additionally, a method variant of the described type can also be developed in that the electronic control unit is able to use an algorithm or a plurality of algorithms for autonomously discharging or partially discharging the superconducting MR magnetic coil system from a charged state and that this discharging process is fully automatically controlled by the electronic control unit with predefinable boundary conditions.

[0089] As a result, even highly complex self-monitoring charging processes with pauses and variable limit values ​​can be safely and reliably carried out in a temperature-optimized manner, if necessary over a long period of time. This significantly reduces the operating and maintenance costs of the magnet system.

[0090] Preferred embodiments of the method according to the invention are characterized in that the predeterminable temperature setting value T1 ramp and T2 tov And the current setting value I1 that can be pre-determined target and I2 pump Select from the following exemplary and principle operable numerical ranges:

[0091] 2K <T1 ramp ≤5K, preferably about 4.2K;

[0092] 2K≤T2 tov <6K, preferably about 4.2K;

[0093] 50A <I1 target ≤500A, preferably about 250A

[0094] 30A≤I2 pump <400A, preferably about 350A

[0095] 30K≤T shield <77K, preferably about 65K.

[0096] Other pre-defined temperature settings T1 soll 、T2 soll and T3 soll And the pre-defined pressure setting value P1 soll The following value ranges can be selected:

[0097] 5K≤T1 soll ≤20K, preferably about 8K;

[0098] 3K≤T2 soll ≤5K, preferably about 4.2K;

[0099] 250K≤T3 soll ≤300K, preferably about 280K

[0100] 10 -4 mbar≤P1 soll ≤10 -1 mbar, preferably about 10 -3 mbar.

[0101] These values ​​are used when the MR coil system contains LTS conductors (low temperature superconductors), which typically operate at liquid helium temperatures, ie below 4.2 K. The cryogenic fluid in the neck is therefore helium.

[0102] T1 soll This corresponds to the temperature from which the vacuum must be reestablished in the vacuum vessel.

[0103] T2 soll This corresponds to the operating temperature of the MR magnet coil system when using LTS conductors.

[0104] T3 soll Corresponds to the temperature of a fully heated solenoid coil system.

[0105] P1 soll This is the lowest vacuum level in the vacuum chamber, starting from which it can be assumed that only a small amount of residual gas is still present and cooling can therefore begin.

[0106] The magnetic resonance (= "MR") device described above for carrying out the method according to the invention also falls within the scope of the invention. In an advantageous embodiment, the device can be designed so that the vacuum pump is of at least two-stage construction and has a turbomolecular pump and a backing pump for the turbomolecular pump, preferably a diaphragm pump. The two pumps are preferably connected in series. Usually, only such a two-stage pump can achieve a sufficiently high vacuum.

[0107] Furthermore, the cryostat for cooling the MR electromagnetic coil system, which has likewise been described above and is necessary for the MR system according to the invention, can be improved in such a way that the end of the fluid line connected to the cavity leads via a second shutoff valve into the region of the vacuum line between the first shutoff valve and the turbomolecular pump, and the end of the fluid line connected to the pressure vessel leads via a third shutoff valve into the region of the vacuum line between the turbomolecular pump and its backing pump. These separate valves allow the helium supply to be arranged separately from the vacuum pump, so that the helium supply cannot be emptied when pumping at the neck tube.

[0108] A control unit for carrying out the method according to the invention, such as has also been described above, also falls within the scope of the invention.

[0109] Embodiments of the control unit according to the invention are particularly preferred, which are characterized in that a control unit for measuring the current pressure P in the cavity of the cooling arm surrounding the cold head is provided. HR The second pressure sensor is connected to the measuring unit, and the actuation unit is configured to open and close the second stop valve and the third stop valve.

[0110] If the solenoid system is still hot, HR The measurement of is used to monitor the pressure during the initial flushing of the neck tube with He. In this process, the neck tube is alternately evacuated via V2 using a vacuum pump, preferably a diaphragm pump when using a two-stage pump, and filled via V1 with helium, so that as little foreign gas as possible is present in the neck tube before cooling.

[0111] P HR The measurement is also used to monitor whether there is enough helium in the pressure vessel after cooling has been completed in order to monitor the filling of the neck tube with helium. It is also used to check the pressure gauge setting on the helium pressure vessel during operation so that no overpressure or underpressure occurs in the supply line.

[0112] In practice, the following improvements of these embodiments have proven themselves, in which there is a connection from the neck tube to a vacuum pump, and the control unit regulates the control of the valve V2 to the vacuum pump. On the one hand, the vacuum pump is used to completely remove foreign gases from the neck tube before cooling begins in the case of a strong heating of the cryostat. This prevents the foreign gases from freezing, which could affect the function of the cold head. On the other hand, the vacuum pump can then be used in a cold state in order to delay the heating of the cryostat by pumping out the existing helium in the event of a failure of the cold head. The control unit regulates the actuation of V2 and the vacuum pump as a function of the measured parameters.

[0113] Alternatively or in addition, another refinement is characterized in that a connection from the helium supply to the neck is present and the control device regulates the control of the He supply via the valve. In this way, after a power failure or water failure, the helium can be liquefied in a controlled manner in order to refill the small stock in the neck. This ensures that there is always enough liquid helium in the neck to last for several hours without quenching in the event of a cooler failure.

[0114] Very particularly preferred is the use of the method variant and the device according to the invention in the field of magnetic resonance, in particular in NMR spectrometers and in MRI devices.

[0115] Further advantages of the present invention are apparent from the description and the drawings. Likewise, according to the present invention, the above-mentioned features and those still to be described can each be used individually or in any combination of a plurality. The embodiments shown and described are not to be understood as an exhaustive enumeration, but rather have more exemplary features for describing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0116] The invention is illustrated in the drawings and will be described in detail with reference to exemplary embodiments.

[0117] in:

[0118] Figure 1 A schematic vertical sectional view showing an embodiment of a magnetic resonance system for implementing a single-valve approach of the automatic charging method according to the invention;

[0119] Figure 2 A flow chart showing the basic method sequence of the automatic charging method with thermal overshooting according to the invention is shown in the form of an algorithm as it should be run in a corresponding program in the control unit and is preferably used as follows: Figure 1 The implementation form of the single valve solution in;

[0120] Figure 3 Shown in the preferred Figure 1 A schematic flow chart of the method steps according to the claim in an embodiment of the single valve solution;

[0121] Figure 4 is a schematic vertical sectional view of an embodiment of a magnetic resonance apparatus according to a three-valve solution for implementing the automatic charging method according to the present invention;

[0122] Figure 5 A flow chart showing the basic method sequence of an automatic charging method with thermal overshooting according to the invention in the form of an algorithm to be run in a corresponding program in a control unit and which is preferably used to Figure 4 The implementation form of the three-valve solution;

[0123] Figure 6 Shown in the press Figure 4 A schematic flow chart of the method steps according to the claim in an embodiment of the three-valve solution in a sub-variant with helium liquefaction;

[0124] Figure 7 A simplified structural diagram of a device for autonomously charging a superconducting MR electromagnetic coil system of an MR device according to the invention is shown, the device having a schematic coil system, a charging power source, a pump unit and a control unit for controlling the charging process;

[0125] Figure 8a A schematic timing diagram for the method variant “Charging interruption (=parking) upon reaching a predetermined maximum radiation shield temperature” is shown;

[0126] Figure 8b A schematic timing diagram for the method variant “Charging interruption upon reaching a predetermined maximum coil temperature” is shown;

[0127] Fig. 9A schematic timing diagram showing a method variant of the automatic charging method according to the present invention with multiple thermal overshoots (“thermal overshooting”); and

[0128] Fig.10 is a schematic timing diagram of the drift behavior after charging with and without thermal overshoot. DETAILED DESCRIPTION

[0129] The present invention relates at its core to a specially adapted method for operating a magnetic resonance system 10 (= “MR system”), in particular to autonomous cooling of a superconducting magnet arrangement.

[0130] Figure 1 A particularly simple embodiment of a magnetic resonance system 10 is schematically shown, which has only one valve for carrying out the automatic cooling method according to the invention.

[0131] The device 10 comprises a vacuum vessel 11 having a superconducting MR electromagnetic coil system 12. In MR measurement operation, the MR electromagnetic coil system is dry, i.e. does not contain a refrigerant. Cooling is performed by a cryostat 13 connected to a compressor 13a. The cryostat 13 comprises a neck tube 14, which leads to the MR electromagnetic coil system 12 through a housing 15 of the vacuum vessel 11. A cooling arm 16 of a cold head 17 is arranged in the neck tube 14 of the cryostat 13. A cavity 18 is formed around the cooling arm 16. The cavity 18 is sealed in a fluid-tight manner relative to the MR electromagnetic coil system to be cooled. In the operating state shown here, the cavity 18 is partially filled with a cryogenic fluid 19 (e.g. liquid helium) and gaseous helium.

[0132] A vacuum pump 20 is provided outside the vacuum container 11, and the vacuum pump is configured as a two-stage vacuum pump 20. Here, the vacuum pump 20 includes a turbomolecular pump 20a having a fore pump 20b (e.g., a diaphragm pump). The vacuum pump 20 is connected to the vacuum container 11 via a vacuum pipe 22 using a first stop valve 21 (stop valve V3).

[0133] For measuring the current temperature T on the MR electromagnetic coil system 12 coil The temperature sensor 23 is arranged on the MR electromagnetic coil system 12. The first pressure sensor 24 connected to the vacuum container 11 via the vacuum pipe 22 measures the current pressure P in the vacuum container 11. ist The control unit 40 detects the current temperature T of the MR electromagnetic coil system 12 coil And compare it with the pre-defined temperature setting value. In addition, the control unit 40 detects the current pressure P in the vacuum container 11. istThe pressure is compared with a predetermined pressure setting value. In addition, the control unit 40 is further configured so that the control unit can control the first stop valve 21 , the vacuum pump 20 and the compressor 13 a of the cold head 17 .

[0134] For the method for autonomously charging the superconducting MR electromagnetic coil system 12 according to the present invention, after a suitable cooling process is initiated, an automatic charging procedure is initiated. At this time, a charging current is supplied to the MR electromagnetic coil system 12 from a charging power supply 50 via a current bar 51 .

[0135] The figure also shows a radiation shield 55 which is optionally equipped with a temperature sensor (not shown specifically here) 56. The HTS current bar 51 is thermally connected to the radiation shield 55, thereby ensuring that these HTS components are cooled below the transformation temperature.

[0136] The control unit 40 includes a measuring unit, a control unit and a processor unit. The temperature sensors 23 and 56 are connected to the measuring unit, and the temperature sensors are used to measure the current temperature T on the MR electromagnetic coil system 12 or on the radiation shield 55. coil and T istshield In addition, a pressure sensor 24 is connected to the measuring unit, by means of which the current pressure P in the vacuum container 11 is measured. ist . The control unit is connected to the first stop valve 21, and the control unit can open and close the first stop valve. In addition, the control unit is connected to the vacuum pump 20 and the cold head 17 (or the compressor 13a), and the control unit can activate and deactivate the vacuum pump and the cold head. The processor unit is arranged between the measuring unit and the control unit. The processor unit compares the parameters detected by the temperature sensor 23 and the pressure sensor 24 with the set parameters. These data are processed by the processor unit and used to control the cold head 17, the vacuum pump 20, the stop valve 21 and especially the charging power supply 50.

[0137] The current pressure P in the cavity 18 can be measured by means of a second pressure sensor 25 connected to a connection 28 leading from a helium supply 29 into the cavity 18 of the cryostat 13 . HR The second pressure sensor 25 is likewise connected to the measuring unit of the processor unit.

[0138] The basic sequence of the charging method according to the invention for an embodiment with thermal overshoot and with only one valve is as follows: Figure 2 is shown as a flow chart.

[0139] Example:

[0140] In a 1-valve variant, the process of the charging method according to the invention may comprise the following steps:

[0141] After the cooling process (a1) of the magnet is complete and the cooling is still switched on, the charging process can be started by starting the current charging procedure (a2), which can also be started by a non-specialist by simply operating a corresponding switch. This procedure runs through the method in such a way that first (b1) the current temperature T is measured. coil and if necessary measure T istshield If these temperatures have reached target values, starting from which the MR electromagnetic coil system 12 and the HTS current rods are superconducting and can be charged, in step (b2) a charging current is supplied to the MR electromagnetic coil system 12 and the MR electromagnetic coil system 12 is charged with current.

[0142] During charging, the target current is set sequentially step by step according to the charging plan adapted for the magnet. If the measured current is close to the corresponding set current, the next level is set. The charging voltage is set according to the charging plan based on the measured current. Finally, the target current I is reached. 1target Once you reach I 1target , charging power 50 automatic stabilization I 1target , in which the charging power supply reduces the charging voltage to 0V (switches from voltage regulation to current regulation).

[0143] While charging, continuously check T coil and T istshield temperature, and also checks cooling and, if necessary, the function of the monitoring sensors. As soon as an error message is received in the control unit 40, the charging process is interrupted and the switch to "parking" is initiated. In the "parking" state, the target current is first set to the currently measured current, and the voltage is set to 0 V, and the main heater 52" and the shield heater 53" are also deactivated. The current is allowed to flow out of the current bar 51 and further cooling is carried out until the set temperature is reached again, and then the process continues with step (b1).

[0144] Furthermore, during charging, in step (c), the current I currently flowing in the MR electromagnetic coil system 12 is measured. coil And compare it with the first current setting value I 1target By comparison, under the first current setting value, the MR electromagnetic coil system 12 generates a desired magnetic field strength. Optionally, in step (d), steps (b1), (b2) and (c) may be repeated until I coil =I 1target When this value is reached, thermal overshoot is achieved by stopping cooling in step (d1) and monitoring the temperature in (d2). Once T coil =T2 tov, cooling begins again (d3). Next, the magnet meets the specifications and the current charging procedure is ended in step (e).

[0145] Figure 3 A schematic flow chart of an autonomous charging method with all method steps according to the invention is shown for an embodiment with only one valve.

[0146] Figure 4 A particularly simple exemplary embodiment of a magnetic resonance system 10 (MR system) having three valves for carrying out the automatic cooling method according to the invention is schematically shown.

[0147] The MR device 10 includes a vacuum vessel 11 with a superconducting MR electromagnetic coil system 12. In MR measurement operation, the MR electromagnetic coil system is dry, that is, it does not contain a refrigerant. Cooling is performed by a cryostat 13 connected to a compressor 13a. The cryostat 13 includes a neck tube 14, which leads to the MR electromagnetic coil system 12 through an outer shell 15 of the vacuum vessel 11. The cooling arm 16 of the cold head 17 is arranged in the neck tube 14 of the cryostat 13. A cavity 18 is formed around the cooling arm 16. The cavity 18 is sealed in a fluid-tight manner relative to the MR electromagnetic coil system to be cooled. In the operating state shown here, the cavity 18 is partially filled with a cryogenic fluid 19 (for example, liquid helium) and gaseous helium.

[0148] A vacuum pump 20 is arranged outside the vacuum container 11, and the vacuum pump is configured as a two-stage vacuum pump 20. Here, the vacuum pump 20 includes a turbomolecular pump 20a with a fore pump 20b (e.g., a diaphragm pump). The vacuum pump 20 is connected to the vacuum container 11 via a vacuum pipe 22 using a first shutoff valve 21 (shutoff valve V3). In addition, the vacuum pump 20 is connected to the neck tube 14 via a connecting structure 26 using a second shutoff valve 27 (shutoff valve V2).

[0149] A temperature sensor 23 is provided on the MR electromagnetic coil system 12 for measuring the current temperature T coil The first pressure sensor 24 connected to the vacuum container 11 via the vacuum pipe 22 measures the current pressure P in the vacuum container 11. ist The second pressure sensor 25 connected to the neck tube 14 via the connection structure 26 measures the current pressure P in the neck tube. HR The control unit 40 (not shown here) detects the current temperature T of the MR electromagnetic coil system 12. coil And compare it with the pre-defined temperature setting value. In addition, the control unit 40 detects the current pressure P in the vacuum container 11. istThe pressure is compared with a predetermined pressure setting value. In addition, the control unit 40 is further configured so that the control unit can control the first stop valve 21 , the vacuum pump 20 and the compressor 13 a of the cold head 17 .

[0150] The control unit 40 includes a measuring unit, a control unit and a processor unit. The temperature sensor 23 is connected to the measuring unit, and the current temperature T of the MR electromagnetic coil system 12 is measured by the temperature sensor. coil In addition, the first pressure sensor 24 is connected to the measuring unit, and the current pressure P in the vacuum container 11 is measured by the first pressure sensor. ist The second pressure sensor 25 is also connected to the measuring unit, and the current pressure P in the neck tube 14 is measured by the second pressure sensor. HR The control unit is connected to the first stop valve 21 , the second stop valve 27 and the third stop valve 30 (stop valve V1 ), and can open and close these stop valves.

[0151] The shut-off valve 30 is integrated in the connection structure 28 connecting the helium supply device 29 to the neck tube 14. In addition, the control unit is connected to the vacuum pump 20 and connected to the cold head 17 via the compressor 13a, and the control unit can activate and deactivate the vacuum pump and the cold head. The processor unit is arranged between the measuring unit and the control unit. The processor unit compares the parameters detected by the temperature sensor 23, the pressure sensor 24 and the pressure sensor 25 with the set parameters. These data are processed by the processor unit and used to control the cold head 17, the vacuum pump 20, the shut-off valves 21, 27, 30 and the charging power supply 50.

[0152] In this embodiment, the charging current is also supplied from the charging source 50 via the current bar 51 to the MR magnetic coil system 12. Furthermore, a radiation shield 55 is shown here, which is optionally equipped with a temperature sensor (also not shown specifically here).

[0153] exist Figure 5 The basic sequence of the charging method according to the invention for an embodiment with three valves is shown in FIG.

[0154] Example:

[0155] In the 3-valve variant, the process of the charging method according to the invention may comprise the following steps:

[0156] After the cooling process (a1) of the magnet is complete and the cooling is switched on, the charging process can be started by starting the current charging procedure (a2), which can also be started by a non-specialist by simply operating a corresponding switch. This procedure runs through the method in such a way that first (b1) the current temperature T is measured.coil and if necessary measure T istshield If these temperatures have reached target values, starting from which the MR electromagnetic coil system 12 and the HTS current rods are superconducting and can be charged, in step (b2) a charging current is supplied to the MR electromagnetic coil system 12 and the MR electromagnetic coil system 12 is charged with current.

[0157] During charging, the target current is set sequentially step by step according to the charging plan adapted for the magnet. If the measured current is close to the corresponding set current, the next level is set. The charging voltage is set according to the charging plan based on the measured current. Finally, the target current I is reached. 1target Once you reach I 1target , charging power automatically stabilizes I 1target , in which the charging power supply reduces the charging voltage to 0V (switches from voltage regulation to current regulation).

[0158] While charging, continuously check T coil and T istshield temperature, and also checks the cooling and the functionality of the necessary monitoring sensors. As soon as an error report is received in the control unit 40, the charging process is interrupted and the switch to "parking" is started. In the "parking" state, the target current is first set to the currently measured current, and the voltage is set to 0V, and the main heater 52" and the shield heater 53" are also deactivated. The current is allowed to flow out of the current bar 51 and further cooling is carried out until the set temperature is reached again, and then the process continues with step (b1).

[0159] Furthermore, during charging, in step (c), the current I currently flowing in the MR electromagnetic coil system 12 is measured. coil and compare it with the first current setting value I 1target In contrast, at the first current setting value, the MR electromagnetic coil system 12 generates the desired magnetic field strength. In order to achieve improved cooling performance during charging, especially when the charging current is increased beyond the setting value and there is a risk of heating the superconductor, the vacuum pump 20 is started in the intermediate steps (c0') and (c0") and the first shut-off valve 27 is opened so that liquid helium is pumped out of the neck tube. Charging can continue during the pumping.

[0160] Optionally (d), steps (b1), (b2) and (c) may be repeated until I coil =I 1target When this state is reached, thermal overshoot is achieved by stopping cooling in step (d1) and the temperature is monitored in (d2). Once T coil =T2 tov, cooling begins again (d3). Next, the magnet meets the specification and the current charging procedure is ended in step (e).

[0161] exist Figure 6 Detailed description of the invention shows a schematic flow chart of an autonomous charging method according to the invention having the method steps according to the invention for an embodiment with three valves.

[0162] Figure 7 A simplified structural diagram of a device for autonomously charging a superconducting MR electromagnetic coil system 12 of an MR device 10 according to the present invention is shown, wherein the MR device has a schematically shown coil system, which includes a main coil 52 with a main switch 52' and a main heater 52", and a shielding coil 53 with a shielding switch 53' and a shielding heater 53", the MR device also has a charging power supply 50, a current rod 51, a pump unit with one or more vacuum pumps 20 and a control unit 40 for controlling the charging process.

[0163] Typically, the magnet charger 50 is controlled via an interface via Ethernet. In order to charge the main coil 52, the main switch 52' must be opened, which occurs by heating a portion of the main coil 52 with a main heater 52". As a result, the heated portion loses superconductivity and the main switch 52' is open. Correspondingly, when the charging process is completed, the main switch 52' is closed in order to short-circuit the superconducting main coil 52. When the charging process is interrupted, for example when a predetermined coil temperature or shield temperature is exceeded, the main switch 52' is also closed before the current is allowed to flow out of the current bar.

[0164] The shielding coil 53 is used to compensate for external magnetic field interference. During the charging / discharging process, the shielding coil 53 is inductively charged until a quench occurs. To prevent this, during charging and discharging, the shielding coil 53 is turned on / off by a shielding switch 53', which is achieved by heating by a shielding heater 53".

[0165] Figure 8a The time course of the method variant “stop upon reaching a predefined maximum radiation shield temperature” is schematically shown.

[0166] Here a typical charging process is shown with multiple pumps during charging. The thick dashed curve represents the charging current, while the charging voltage is represented by the solid curve. Radiation shield temperature T istshield The coil temperature T is indicated by the thin dashed line. coil Indicated by dotted lines.

[0167] By pumping during charging, the charging losses are compensated to such an extent that a slight increase in the coil temperature can be detected. Charging is carried out in stages at different voltages U1, U2, U3 and U4. By reducing the charging voltage, further charging losses are minimized, thereby further reducing the coil temperature. However, as the charging current increases, the radiation shield temperature T istshield Also increases, since the power supply (practically always designed as an HTS part) is thermally coupled to the radiation shield 55. If the limiting value T on the radiation shield 55 is exceeded, max In this case, for a charging current of 350 A, the charging algorithm stops the magnet: the superconducting switches 52', 53' are closed, allowing current to flow out of the feeder. At this point, the magnet cools, and thus the radiation shield temperature T istshield The pumping is still carried out at the neck 14 in order to accelerate the cooling process. Once the characteristic radiation shield temperature is reached, the charging process is activated again until the current setting value I is reached. Target . Next comes “thermal overshoot”.

[0168] Figure 8b The corresponding timing diagram for the method variant "Stop upon reaching a predetermined maximum coil temperature" is shown schematically. Figure 8a The curve is similar to that in Figure 1, but here the charging is carried out at a constant charging voltage U1, which causes the coil temperature to continue to rise until T coil =T ramp In this example, the coil temperature T ramp Serves as an interruption ("parking") criterion. Here, a cooling process takes place during the charging interruption without pumping out the helium in the neck tube. This variant is preferably used for smaller magnets (<9 T).

[0169] Fig. 9 A schematic timing diagram shows a method variant of the automatic charging method according to the invention with multiple thermal overshoots.

[0170] When the first current setting value I1 is reached target Afterwards, a thermal overshoot method variant is performed, and at the first current setting value, the MR electromagnetic coil system 12 generates the desired magnetic field strength. In the embodiment shown, a plurality of thermal overshoots, here a total of four, are experienced. Here, by shutting down the cooling, the coil temperature T coil respectively to a predetermined second temperature setting value T2 tov <T CAt the second temperature setting, the superconducting current carrying capacity of the MR electromagnetic coil system 12 is reduced to a desired lower value, while the superconductivity in the electromagnetic coil system 12 does not exceed the critical transition temperature T when transitioning from the normal conducting state to the superconducting state. C And there will be no complete collapse. The maximum temperature T2 tov Close to the critical transition temperature T C , but there is a safety margin typically on the order of about 100mK.

[0171] With each thermal overshoot cycle, the superconductor of the MR electromagnetic coil system 12 is slightly more stressed, which ultimately achieves an optimized current distribution in the superconducting filament. As a result, a defined drift of the MR electromagnetic coil system 12 is achieved more quickly than, for example, in a bath-cooled magnet system or in a system without thermal overshoot.

[0172] Alternatively, the coil temperature can be kept at the maximum temperature T2 for a longer period of time. tov , rather than performing multiple overshoot cycles. However, this alternative is less practical because the cold head used is not suitable for maintaining a constant temperature.

[0173] at last, Fig.10 The time course of the drift behavior of the MR electromagnetic coil system 12 after charging with and without thermal overshoot is shown:

[0174] After charging a superconducting magnet in "continuous mode", a decaying behavior of the magnetic field over time usually occurs. This can usually be explained by recoupling in the superconducting filaments. Only then does a drift behavior caused by the conductors and connections occur, with typical values ​​of less than 0.05 ppm / h. However, depending on the specific magnet type and conductor type, this "natural" decaying behavior can last for days or weeks. Through targeted use of thermal overshoot, this decaying behavior can be significantly shortened and, depending on the specific magnet system, typical long-term drift values ​​can be reached within a few hours. Fig.10 In the process with thermal overshoot shown by way of example in FIG. 1 , a plurality of, in this example four, overshoot steps can be clearly seen.

[0175] Reference numerals list

[0176] 10 Magnetic resonance (= “MR”) equipment

[0177] 11 Vacuum container

[0178] 12 MR electromagnetic coil system

[0179] 13 Cryostat

[0180] 13a Compressor

[0181] 14 Neck

[0182] 15. Housing

[0183] 16 Cooling Arm

[0184] 17 Cold Head

[0185] 18 Cavity

[0186] 19 cryogenic fluids

[0187] 20 Vacuum pump

[0188] 20a Turbomolecular pump

[0189] 20b Backing pump

[0190] 21 Stop valve (V3)

[0191] 22 Vacuum pipe

[0192] 23. Temperature sensor

[0193] 24 First pressure sensor

[0194] 25 Second pressure sensor

[0195] 26 Connecting pipe (from neck tube to vacuum pump)

[0196] 27 Stop valve (V2)

[0197] 28 Connect the pipe (from the helium supply to the neck tube)

[0198] 29 Helium supply device

[0199] 30 Stop valve (V1)

[0200] 40 Control Unit

[0201] 50 Charging Power Supply

[0202] 51 Current rod

[0203] 52 Main coil

[0204] 52' Main switch

[0205] 52” Primary Heater

[0206] 53 Shielding Coil

[0207] 53' Muting switch

[0208] 53” Shielded Heater

[0209] 55 Radiation Shield

[0210] 56 Temperature sensor.

[0211] References

[0212] Publications considered for the purpose of assessing patentability:

[0213] [0] DE 10 2021 206 392.6

[0214] [1] DE 10 2016 218 000 B3≈WO 2018 / 054648 A1≈EP 3296 669B1≈CN107845474 B≈JP 6338755 B≈US10 101 420 B2

[0215] [2] US 8 729 894 B2

[0216] [3] US2005 / 0111159 A1

[0217] [4] DE 10 2014 218 773 B4≈CN 105501679 B≈GB 2532322B≈US10 203 067B2

[0218] [5]DE 10 2015 215 919 B4≈GB 2542667 B≈US10 203068B2

[0219] [6] US2021 / 0080527 A1

Claims

1. A method for operating a magnetic resonance (MR) system (10), comprising a superconducting MR electromagnetic coil system (12) which is arranged in a vacuum vessel (11) and which is dry (refrigerant-free) in MR measurement operation, and a cryostat (13) for cooling the MR electromagnetic coil system (12), the cryostat comprising a neck tube (14) which leads through a housing (15) of the vacuum vessel (11) to the MR electromagnetic coil system (12), wherein: The cooling arm (16) of the cold head (17) is at least partially arranged in the neck tube (14) and cools the superconducting MR electromagnetic coil system (12) to a superconducting temperature before supplying a charging current. Characterized in that the method comprises the following steps: To autonomously charge the superconducting MR electromagnetic coil system (12): (a1) starting the cooling process of the superconducting MR electromagnetic coil system (12); (a2) starting an automatic current charging procedure for the superconducting MR electromagnetic coil system (12); (b1) Measure the current temperature T on the MR electromagnetic coil system (12) coil , and T coil The first temperature setting value T1 can be predetermined ramp In contrast, starting from the first temperature setting value, the MR electromagnetic coil system (12) is superconducting and should be charged; (b2) If T coil ≤T1 ramp : supplying a charging current to the MR electromagnetic coil system (12), and charging the MR electromagnetic coil system (12) with the current; (c) Measuring the current I flowing in the MR electromagnetic coil system (12) coil , and I coil and a first current setting value I1 which can be predetermined target In comparison, the MR electromagnetic coil system (12) generates a desired magnetic field strength at a first current setting; (d) Repeat steps (b1), (b2) and (c) until I coil =I1 target ; (e) Shutting down the current supply to the MR electromagnetic coil system (12) and stopping the automatic current charging process.

2. The method according to claim 1, characterized in that The following intermediate steps are performed between step (d) and step (e): (d1) Once I coil =I1 target : stopping the cooling process of the superconducting MR electromagnetic coil system (12); (d2) Measuring the current temperature T on the MR electromagnetic coil system (12) coil , and T coil The second temperature setting value T2 can be predetermined tov <T C By comparison, at the second temperature setting value, the superconducting current carrying capacity of the MR electromagnetic coil system (12) is reduced to a predeterminable lower value, while the superconductivity in the electromagnetic coil system (12) does not exceed the critical transition temperature T when changing from the normal conducting state to the superconducting state. C And it won’t completely collapse; (d3) Once T coil =T2 tov : Restart the cooling process of the superconducting MR electromagnetic coil system (12).

3. The method according to claim 2, characterized in that When the criterion T is reached in step (d3) coil =T2 tov Thereafter, steps (d1) to (d3) are repeated multiple times.

4. The method according to any one of the preceding claims, characterized in that If in step (b2) T coil >T1 ramp , the charging of the MR electromagnetic coil system (12) with current is interrupted, and the cooling process continues until T coil ≤T1 ramp ; Thereafter, the process is resumed with step (b1).

5. The method according to any one of the preceding claims, characterized in that A closed cavity (18) is formed around the cooling arm (16), which cavity is sealed in a fluid-tight manner relative to the MR electromagnetic coil system (12) to be cooled and is at least partially filled with liquid helium (19) during normal operation of the MR system (10). The neck tube (14) is connected to a helium supply (29) via a first valve V1 (30), through which helium can be introduced on the one hand in order to liquefy it at the cooling arm, and on the other hand, during steps (c) and (d), the helium in the neck tube (14) can be pumped out via the helium supply. The method comprises the following steps: (c0') measures the current I currently flowing in the MR electromagnetic coil system (12) coil , and I coil and a second current setting value I2 which can be predetermined pump <I1 target In contrast, starting from the second current setting value, the helium in the neck tube (14) should be pumped out; and (c0”) Once I coil ≥I2 pump : Activate the vacuum pump (20) arranged outside the vacuum container (11), open the first stop valve (27) in the pump-out pipe (26) introduced from the vacuum pump (20) into the neck tube (14), so as to use the vacuum pump (20) to pump helium out of the neck tube.

6. The method according to claim 5, characterized in that The supply pipe (26) leading to the neck tube (14) is connected to the vacuum pump (20) through another valve V3 (30), and helium is supplied to the neck tube (14) and liquefied in step (f).

7. The method according to any one of the preceding claims, characterized in that In step (b1), the current temperature T at the radiation shield (55) is additionally measured. istshield , and compare it with the pre-determined temperature setting value T shield Compared with, and if T istshield ≤T shield , then supply charging current according to step (b2).

8. The method according to claim 7, characterized in that If T istshield >T shield , the charging of the MR electromagnetic coil system (12) with current in step (b2) is interrupted, and the cooling process is continued until T istshield ≤T shield , thereafter resuming the process with step (b1).

9. The method according to any one of the preceding claims, characterized in that Predeterminable temperature setting value T1 ramp and T2 tov And the current setting value I1 that can be pre-determined target and I2 pump Select from the following value ranges: 2K <T1 ramp ≤5K, preferably about 4.2K; 2K≤T2 tov <6K, preferably about 4.2K; 50A <I1 target ≤500A, preferably about 250A 30A≤I2 pump <400A, preferably about 350A 30K≤T shield <77K, preferably about 65K.

10. The method according to any one of the preceding claims, characterized in that The autonomous charging process of the superconducting MR electromagnetic coil system (12) is automatically regulated by means of an electronic control unit (40), which is configured to detect the current temperature T on the MR electromagnetic coil system (12). coil The temperature is compared with a predetermined temperature setting value and used to detect the current I currently flowing in the MR electromagnetic coil system (12). coil This is compared with a predetermined current setting value and used, if necessary, to control the valves (21; 27; 30), the charging power source (50), the vacuum pump (20) and the functional units for controlling the cold head (17).

11. The method according to claim 10, characterized in that The electronic control unit (40) controls the autonomous charging process of the superconducting MR electromagnetic coil system (12) fully automatically by means of an algorithm, taking into account various measured values ​​and parameters, even during the absence of an operator or monitoring personnel, at night, in particular for several days, without interruption in time, and during the autonomous charging process of the superconducting MR electromagnetic coil system (12), the electronic control unit (40) independently detects critical state changes and disturbances of the superconducting MR electromagnetic coil system (12) and of a cryostat (13) for cooling the MR electromagnetic coil system (12), in particular state changes and disturbances of temperature, current and pressure values ​​in the vacuum vessel (11), and responds thereto by using a predefinable alternative algorithm for further regulating the autonomous charging process and / or by sending a message or fault report, such as an e-mail message, to the operator or monitoring personnel.

12. The method according to any one of claims 10 or 11, characterized in that The electronic control unit (40) is capable of using at least one algorithm for autonomously discharging or partially discharging a superconducting MR magnetic coil system (12) from a charged state and regulating this discharge process fully automatically by the electronic control unit (40) using predefinable boundary conditions.

13. A magnetic resonance (MR) system (10) for carrying out the method according to claim 1, comprising a superconducting MR electromagnetic coil system (12) which is arranged in a vacuum vessel (11) and which is dry (refrigerant-free) in MR measuring mode, and a cryostat (13) for cooling the MR electromagnetic coil system (12), the cryostat comprising a neck tube (14) which leads through a housing (15) of the vacuum vessel (11) to the MR electromagnetic coil system (12), wherein: A cooling arm (16) of a cold head (17) is at least partially arranged in a neck tube (14), a closed cavity (18) being formed around the cooling arm (16), said cavity being sealed in a fluid-tight manner with respect to an MR magnet system (12) to be cooled and being filled at least partially with a cryogenic fluid (19) during normal operation of the MR system (10), characterized in that A vacuum pump (20) is arranged outside the vacuum container (11), and a first stop valve (21) is arranged in a vacuum pipe (22) introduced from the vacuum pump (20) into the vacuum container (11). There is a method for measuring the current temperature T on the MR electromagnetic coil system (12) coil A temperature sensor (23) and a pressure sensor for measuring the current pressure P in the vacuum container (11) ist a first pressure sensor (24), The control unit (40) is configured to detect a current temperature T on the MR electromagnetic coil system (12). coil The temperature is compared with a predetermined temperature setting value and used to detect the current pressure P in the vacuum container (11). ist The pressure is compared with a predetermined pressure setting value and used to control the first stop valve (21), the vacuum pump (20), the cold head (17) and the charging power source (50).

14. A control unit (40) for use in an MR system (10) for implementing the method according to any one of claims 1 to 12, the control unit (40) being configured to detect a current temperature T at the MR electromagnetic coil system (12). coil The temperature is compared with a predetermined temperature setting value and used to detect the current pressure P in the vacuum container (11). ist and compares it with a predetermined pressure setting value, characterized in that: The control unit (40) has a measuring unit for measuring the current temperature T on the MR electromagnetic coil system (12). coil A temperature sensor (23) and a temperature sensor (23) for measuring the current pressure P in the vacuum container (11) ist A pressure sensor (24) is connected to the measuring unit, The control unit (40) comprises a control unit for opening and closing the first shut-off valve (21), for activating and deactivating the vacuum pump (20), and for activating and deactivating the cold head (17). The control unit (40) includes a processor unit, which is arranged as an interface between the measuring unit and the control unit to compare the detected sensor parameters with the set parameters and process data for controlling the cold head (17), the vacuum pump (20), the stop valve (21) and the loading power supply (50).

15. The control unit according to claim 14, characterized in that There is a connection structure (26) from the neck tube (14) to the vacuum pump (20), and the control unit (40) regulates the control from the valve V2 (27) to the vacuum pump (20), there is a connection structure (28) from the helium supply device (29) to the neck tube (14), and the control unit (40) regulates the control of the helium supply device (29) through the valve (30).

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