Self-cooling of dry-cooled superconducting MR magnet coil systems

Abstract

The invention relates to a method for operating an MR device with an MR magnet coil system, having the following steps: measuring a current temperature T of the magnet ist and comparing T ist with a first temperature setpoint T1 soll and, from the first temperature setpoint, carrying out a pumpdown of the vacuum vessel; if T ist > T1 soll , activating a vacuum pump and opening a first shut-off valve in a vacuum line of the vacuum pump to the vacuum vessel; measuring a current pressure P in the vacuum vessel ist and comparing P ist with a first pressure setpoint P1 soll at which the magnet coil system should be cooled to a cryogenic temperature; if P ist < P1 soll , activating a cooling head in order to cool a cooling arm; measuring a current temperature T on the magnet coil system ist and comparing T ist with T1 soll ; if T ist < T1 soll , switching off the first shut-off valve and the vacuum pump; measuring a current temperature T on the magnet ist and comparing T ist with a second temperature setpoint T2 soll and maintaining T2 soll , at which a run temperature of the magnet coil system for MR measurements is reached. The magnet coil system can thus be cooled autonomously.

Description

Technical Field

[0001] The present invention relates to a method for operating a magnetic resonance (“MR”) device having a dry (“refrigerant-free”) superconducting MR coil system disposed in a vacuum container during MR measurement operation and a cryostat for cooling the MR coil system, the cryostat including a neck tube extending through the outer shell of the vacuum container to the MR coil system, a cooling arm of a cooling head being at least partially disposed in the neck tube, forming a closed cavity around the cooling arm, the cavity being fluid-tightly sealed relative to the MR coil system to be cooled and at least partially filled with a cryogenic fluid during normal operation of the MR device. Background Technology

[0002] This method and the corresponding MR equipment are known from DE 10 2016 218 000B3 (= Reference [1]).

[0003] This invention generally relates to the field of cooling superconducting magnet systems that should / must be maintained at very low (i.e., cryogenic) temperatures during operation. Such superconducting magnet systems are used, for example, in the field of magnetic resonance imaging, such as in MRI (magnetic resonance imaging) tomography scanners or NMR (nuclear magnetic resonance) spectrometers.

[0004] Nuclear magnetic resonance (NMR) is a high-performance instrumental analytical method, particularly useful for determining the chemical composition of samples. Here, high-frequency pulses are injected into the sample within a strong static magnetic field, and the electromagnetic response of the sample is measured. The particularly homogeneous strong static magnetic field in NMR is often generated by a superconducting magnet system; therefore, during measurement operations, the magnet system must, in most cases, be cooled to near absolute zero using liquid helium as a cryogenic fluid.

[0005] Such superconducting magnet systems are typically also equipped with active cooling. In this case, the system usually no longer has a fluid chamber in which the magnet is directly surrounded by a cryogenic fluid. Instead, the coils of the magnet system are housed in a vacuum container and are thus “dry” during MR measurement operations, i.e., without refrigerant. Typically, a radiation shielding layer surrounds the vacuum container, but sometimes this includes the magnet system being cooled directly by an active cooler, such as a pulse tube cooler or a Gifford-MacMahon cooler.

[0006] Dry systems are generally more susceptible to cooling system failures, such as when the cooling head fails, because unlike bath-cooled magnet systems, there is no temperature buffer, typically in the form of liquid refrigerant, directly surrounding the magnet. This refrigerant can evaporate and thus maintain a low temperature for an extended period when the cooling system fails. In contrast, bath-cooled systems require more manpower and are more expensive to operate initially, as large quantities (up to several 1000-liter units) of liquid helium and nitrogen are needed for cooling and filling, and must be replenished with liquid helium and nitrogen in the event of a quench. Therefore, bath-cooled systems cannot operate independently.

[0007] The use of active cooling systems significantly reduces the consumption of expensive liquid helium, improves the availability of NMR equipment, and also helps to reduce structural height. Active cooling systems can be constructed as single-stage or multi-stage systems. In multi-stage systems, the heat radiation shielding layer is typically cooled by a hotter cooling stage, while the object to be cooled is cooled by a cooler cooling stage.

[0008] DE 20 2017 001 501U1 (=Reference [2]) describes a monitoring device for a gradient system in an MR device to ensure reliable operation of the magnetic coil. The device includes a temperature sensor that sends temperature measurement results to a safety unit. The safety unit then initiates various actions, such as issuing warnings to the user, interrupting operation, or changing the order of parameters and measurement sequences. In addition, a cooling system is provided to actively cool the components (power amplifiers) of the gradient system. Reference [2] neither describes nor implies a superconducting magnet system that can autonomously reach low temperatures.

[0009] EP 3 454 071A1 (= Reference [3]) describes a method for monitoring the function of a cooling system for an MR device. Temperature sensors are provided on different components or disposed on said components as part of the magnetic resonance device, and the temperature sensors provide corresponding temperature values ​​as measurement data. The magnetic resonance device includes a cooling system that uses water as a coolant to cool the components to be cooled in different cooling branches, in which the components can be cooled sequentially. Flow sensors may also be used. The sensor data are compared with reference values ​​and evaluated in order to take appropriate measures. Reference [3] does not disclose a method for cooling superconductors, especially autonomously, to low temperatures.

[0010] US 8 729 894B2 (= Reference [4]) discloses a magnet system for MRI, the magnet system comprising a container containing liquid refrigerant and a superconducting magnet inside the container, the container being configured such that it is detachably connected to a vacuum pump, the vacuum pump being configured such that it pumps refrigerant from the container to reduce the pressure level inside the container to the pumped pressure level during high-load operation of the superconducting magnet, and to increase the pressure level from the pumped pressure level to the normal operating pressure level, increasing the pressure level during normal magnet operation. Reference [4] also describes a method for charging the magnet, wherein the container with the magnet can be evacuated during a so-called linear ramping. A cooling head is placed in the neck tube without affecting the vacuum in the container. However, in this arrangement, the neck tube is not filled with refrigerant, but a cryostat containing liquid helium. For the present invention, reference [4] constitutes a far-fetched prior art because it relates to a “wet-cooled” coil system in which the measures according to the invention described below cannot be performed at all, and therefore cannot be operated autonomously.

[0011] US 2006 0225433A1 (=Reference [5]) discloses a monitoring system for predicting component failure. The MRI scanner includes a bath-cooled magnet. Multiple sensors are provided to monitor the operation of the scanner. In the illustrated embodiment, sensors are provided inside the cryostat to monitor the temperature and pressure of the container. Other sensors may be provided to monitor cooling components of the cooling system, such as cooling heads and compressors. These sensors provide data about the operation of the scanner to the monitoring circuit. In addition, the monitoring circuit includes an intermediate database and an algorithm as well as a processor. The intermediate database is configured to store data about the operation of the scanner. The algorithm is configured in conjunction with the processor to perform different calculations and processing operations on the data stored in the intermediate database. The corrected data is transmitted to the user interface. The bath-cooled system cannot achieve self-sufficient cooling of the cryostat because the monitoring circuit does not send information to control elements such as pumps. For the present invention, Reference [5], like Reference [4], constitutes only a distant prior art.

[0012] As known from DE 10 2014 218 773B4 (=Reference [6]), in a cryogenic thermostat, the hollow volume between the inside of the neck tube and the cooling arm of the cooling head is filled with a gas, such as helium. During normal operation, the lowest cooling stage of the cooling arm is close to the object to be cooled; for example, a tight thermal coupling is established through the contact between the object to be cooled and the lowest cooling stage with a small amount of liquid helium in the hollow volume. When cooling fails, the gas pressure in the hollow volume increases due to the rise in temperature; the liquid helium that may be present in the hollow volume evaporates. The movably supported cooling head moves away from the object to be cooled by the increased gas pressure in the hollow volume, thereby reducing the thermal coupling between the cooling arm and the object to be cooled. With this cryogenic thermostat, the heat load can be reduced by the cooling arm when active cooling fails, but the structure is expensive because the cooling head is movably suspended. In addition, there is still significant thermal coupling due to the high gas pressure in the hollow volume.

[0013] DE 10 2015 215 919B4 (=Reference [7]) describes a method and apparatus for precooling a cryostat with a heat pipe, such as the cryostat given in Reference [6]. During the precooling phase, the object to be cooled is precooled to a target temperature within the operating range of the cryogenic working medium, in which the heat pipe can operate efficiently. Here, for precooling, a thermally conductive, precisely fitted short-circuit block is inserted into the heat pipe through the neck tube. One free end of the short-circuit block is thermally connected to a high-power cooling device, and its other end is in contact with a hot contact surface. In an intermediate phase after the target temperature is reached, the short-circuit block is removed from the heat pipe, and then, during the operation phase, heat is transferred through the heat pipe during condensation operation. This significantly reduces the time required to precool the cryostat to its operating temperature, thereby significantly reducing the start-up time.

[0014] Reference [1] cited above describes a cryogenic system having a vacuum container and a cooling object disposed within the vacuum container, the vacuum container having a neck tube leading to the cooling object, a cooling arm of a cooling head disposed in the neck tube, forming a closed cavity around the cooling head, the cavity being fluidly sealed relative to the cooling object and filled with a cryogenic fluid during normal operation. This cryogenic system can be used to perform general methods having the aforementioned combination of features, because the refrigerant in the neck tube can evaporate under vacuum for cooling.

[0015] The disadvantage of all currently known methods for cooling a dry, i.e., unrefrigerant-enclosed, superconducting MR magnetic coil system during MR measurement operations is that precooling the magnet system to a cryogenic temperature, typically starting from room temperature, always and inevitably requires a skilled technician to charge the superconducting magnetic coil with an electric current.

[0016] To date, MR equipment cannot operate autonomously without the participation of highly costly, specially trained service technicians during the following operational phases. In principle, these operational phases must always be performed after the user first installs the system, but they must also be performed each time after the superconducting magnet is temporarily heated, for example, during quenching. Summary of the Invention

[0017] In contrast, the present invention, in its more detailed and complex aspects, aims to improve the methods for operating MR devices of the aforementioned type, and also to improve the apparatus for performing the methods, through low-consumption, readily available, or standardly existing technical means, so that the MR magnetic coil system can be cooled to a cryogenic temperature in most cases autonomously and with targeted optimization in terms of defined process parameters, in the simplest manner and without the need for expensive additional components. At this cryogenic temperature, the superconducting MR magnetic coil system can be charged with current. The MR device has a superconducting MR magnetic coil system that is "dry-type" disposed in a vacuum container and has no refrigerant during MR measurement operation, and a cryostat for cooling the system.

[0018] The objective is achieved by the present invention in a surprisingly simple yet equally efficient manner in terms of the method of operation through the following steps:

[0019] (a1) Measure the current temperature T on the MR magnetic coil system ist and T ist With the first temperature setpoint T1 that can be predetermined soll In contrast, the vacuum container should be pumped out starting from the first temperature setpoint;

[0020] (a2) If T ist >T1 soll Then the vacuum pump located outside the vacuum container is activated, and the first shut-off valve in the vacuum line from the vacuum pump to the vacuum container is opened.

[0021] (b1) Measure the current pressure P in the vacuum container ist and P ist With the pre-defined first pressure setpoint P1 sollIn comparison, under the first pressure setting, the MR magnetic coil system should be cooled to a low temperature;

[0022] (b2) If P ist <P1 soll Activate the cooling head to cool the cooling arm (16);

[0023] (c1) Measure the current temperature T on the MR magnetic coil system. ist and T ist Compared with the first temperature setpoint T1 soll In comparison;

[0024] (c2) If T ist <T1 soll Turn off the first shut-off valve and shut down the vacuum pump;

[0025] (d1) Measure the current temperature T on the MR magnetic coil system. ist and T ist With the pre-defined second temperature setpoint T2 soll Compare and maintain the second temperature setpoint T2 soll At the second temperature setting, the operating temperature of the MR magnetic coil system used for MR measurement is reached.

[0026] In the method according to the invention, a sufficiently high vacuum must obviously be generated in the vacuum container before the temperature of the magnetic coil system is cooled below a first temperature setpoint. On the one hand, this vacuum is used to prevent thermal convection inside the container, but on the other hand, it is also used to prevent icing inside the container. After heating, volatile substances may release gases from the magnetic coil system, or air may enter the vacuum container, as is typically the case when the system is first installed. Cooling the temperature below a value below which volatile components condense or freeze (= first temperature setpoint T1) is necessary. soll Before that, these impurities, which are mostly gaseous, are first removed by a vacuum pump. If the value T1 is lower than this in step a1... soll If the value drops below this level in step c1, the vacuum pump can be turned off.

[0027] Therefore, it is also important to detect the current negative pressure in step b1 before starting active cooling.

[0028] In other words, to ensure the long-term functionality of the MR system, the method according to the present invention does not simply involve starting the vacuum pump and cooling in parallel. Instead, it first detects the parameters of temperature and pressure and, if necessary, controls the vacuum and cooling separately based on these parameters. That is, it requires continuous monitoring of temperature and pressure values ​​and appropriate control of the vacuum pump and cooling.

[0029] This results in an operating method that, by means of a simple control unit—almost like pressing a button—independently cools the superconducting magnet system and responds accordingly to external disturbances, generating error reports when necessary and sending them, for example, via email. In this way, the magnetic coil system can operate substantially autonomously and independently, requiring no further intervention from technicians, and can be flexibly adjusted to the operating temperature by the end customer.

[0030] The result is significant savings in service, particularly in terms of professional personnel investment for MR equipment operators, and reduced equipment downtime. The equipment is also more compact, lighter, and more economical in all aspects.

[0031] In other words, the method according to the invention is largely autonomous in order to cool cryostat-based MR devices, especially those used for MRI, to a temperature at which the magnets can be recharged if necessary, a feat not even suggested in the prior art discussed above. Systems based on bath cooling, in particular, are completely unsuitable for this mode of operation.

[0032] The MR apparatus for performing the method according to the invention described above is equipped with a superconducting MR magnetic coil system disposed in a vacuum container, which is dry, i.e., without refrigerant, during MR measurement operation, and a cryostat for cooling the MR magnetic coil system. The cryostat includes a neck tube that extends through the outer shell of the vacuum container to the MR magnetic coil system. A cooling arm of a cooling head is at least partially disposed in the neck tube, forming a closed cavity around the cooling arm. The cavity is fluid-tightly sealed relative to the MR magnetic coil system to be cooled and is at least partially filled with cryogenic fluid during normal operation of the MR apparatus.

[0033] For this type of MR device, the object of the invention is achieved as follows: outside the vacuum container, a vacuum pump and a first shut-off valve are disposed in the vacuum line leading from the vacuum pump to the vacuum container, and a system for measuring the current temperature T on the MR magnetic coil system is provided. ist Temperature sensor and for measuring the current pressure P in the vacuum container ist The first pressure sensor, and the control unit, are configured to detect the current temperature T on the MR magnetic coil system. ist It is then compared with a pre-defined temperature setpoint to detect the current pressure P in the vacuum container. ist It is compared with a pre-defined pressure setting and used to control the first shut-off valve, vacuum pump, and cooling head.

[0034] The cryostat suitable for performing the method according to the invention described above contributes to achieving the object of the invention in such a way that it is provided with a fluid line, one end of which extends into a cavity surrounding a cooling arm of a cooling head, and the other end of which extends into a pressure vessel filled with cryogenic fluid outside the neck tube, and is provided for measuring the current pressure P in the cavity. HR The second pressure sensor.

[0035] Finally, the apparatus for performing the method according to the invention requires an electronic control unit configured to detect the current temperature T on the MR magnetic coil system. ist It is then compared with a pre-defined temperature setpoint and used to detect the current pressure P in the vacuum container. ist The pressure is then compared to a pre-defined pressure setpoint, and the control unit uses an algorithm to control different components, taking into account different measured values ​​and parameters. The control unit is crucial for autonomous cooling functionality because it requires continuous monitoring of temperature and pressure values ​​and the use of a specially designed algorithm to rationally control the vacuum pump and cooling system based on the available measurements.

[0036] The control unit contributes to achieving the object of the invention in such a way that it has a measuring unit for measuring the current temperature T on the MR magnetic coil system. ist Temperature sensor and used to measure the current pressure P in the vacuum container ist A pressure sensor is connected to the measuring unit. Furthermore, the control unit includes an operation unit for opening and closing a first shut-off valve, activating and stopping a vacuum pump, and activating and stopping a cooling head, and includes a processor unit configured as an interface between the measuring unit and the operation unit. The processor unit compares detected sensor parameters with set parameters and processes the data to control the cooling head, vacuum pump, and shut-off valve.

[0037] The particular advantages of the self-cooling method according to the present invention are:

[0038] 1. Implement an automatic cooling program during the initial operation of an MR device with a superconducting magnetic coil system.

[0039] 2. An automatic cooling program is implemented after the cooling unit fails or the electromagnetic coil system overheats due to quenching (=“automatic cooling”).

[0040] 3. Continuous temperature and pressure measurements allow:

[0041] a) Automatically check the current temperature T on the MR magnetic coil system ist ;

[0042] b) Automatically check the current pressure P in the vacuum containerist .

[0043] Variations, preferred embodiments and improvements of the present invention

[0044] The following variations of the method according to the invention can also be advantageous, wherein, in another step, the pressure P of the cryogenic fluid in the neck tube is monitored by a pressure gauge in the supply device for cryogenic fluids, especially helium. HR And keep it between 900mbar and 1100mbar.

[0045] A preferred embodiment of the method according to the invention is characterized in that the neck tube is connected to a helium supply device via a first valve V1, in which case helium is supplied to the neck tube and liquefied in step (e). Thus, during operation of the cooling head, the helium reserve in the neck tube is automatically refilled, and the helium can condense on the cooling head under appropriate pressure. For example, in the event of cooling failure, the helium reserve constitutes a cold buffer. The heat pipe formed in this way guides heat from the coil to the cooling head particularly efficiently, while simultaneously decoupling the mechanical vibrations of the cooler.

[0046] One particularly preferred embodiment of the invention involves a supply line leading to the neck tube connected to a vacuum pump via another valve V2, and the neck tube being emptied using the following steps:

[0047] (a3) Measure the current temperature T on the MR magnetic coil system. ist and T ist With the pre-defined third temperature setpoint T3 soll In comparison, the neck tube should be pumped out starting from the third temperature setpoint; and

[0048] (a4) If T ist >T3 soll Activate the vacuum pump and open the second shut-off valve V2 in the vacuum line leading from the vacuum pump to the neck tube.

[0049] T3 soll This occurs when the MR magnetic coil system is heated for an extended period. In such cases, it is necessary to first remove the foreign gas from the neck tube by evacuation, so that the foreign gas will not freeze when cooled to a low temperature and thus will not negatively affect the functionality of the cryostat. For example, such icing on a safety valve also poses a danger, as the safety valve may no longer be able to open under overpressure.

[0050] Advantageously, steps a3 and a4 are performed before activating the cooling head. After pumping out step a4, fresh helium is preferably refilled via the helium supply device. This is achieved by turning off the pump and (after a short waiting time) opening valve V1, allowing gaseous helium to flow into the evacuated neck tube. A second pressure sensor is used to check whether the supply line and neck tube are filled with helium and whether a stable pressure value has been established at this point. Furthermore, pumping can be performed at the neck tube during charging, thereby generating a lower temperature in the neck tube within a defined time.

[0051] The following improvements to the method are advantageous, characterized in that, in the event of cooling head failure, in step (d2), liquid helium in the neck tube is pumped out using a vacuum pump to cool the MR magnetic coil system. The liquid helium constitutes a cold buffer that can be used to provide emergency cooling. The lower pressure established during the pumping out of the liquid helium causes the helium to convert to a gaseous state, and the heat of vaporization draws additional heat from the cryostat, thereby ensuring additional cooling.

[0052] A preferred embodiment of the method according to the invention is characterized by a pre-defined temperature setpoint T1. soll T2 soll and T3s oll And the pre-defined pressure setpoint P1 soll Selected from the following value range:

[0053] 5K≤T1 soll ≤20K, preferably around 8K;

[0054] 3K≤T2 soll ≤5K, preferably around 4.2K;

[0055] 250K≤T3 soll ≤300K, preferably about 280K

[0056] 10 -4 mbar≤P1 soll ≤10 -1 mbar, preferably about 10 -3 mbar

[0057] These values ​​are used when the MR coil system includes an LTS conductor (low-temperature superconductor), which typically operates at liquid helium temperatures, i.e., less than 4.2 K. Therefore, the cryogenic fluid in the neck is helium.

[0058] T1 soll Corresponding to this temperature, from this temperature onwards, a vacuum must be re-established in the vacuum container.

[0059] T2 sollThis corresponds to the operating temperature of the MR magnetic coil system when using LTS conductors.

[0060] T3 soll The temperature corresponding to the fully heated magnetic coil system.

[0061] P1 soll It is the minimum vacuum level in the vacuum chamber. It can be assumed that from this vacuum level, only a small amount of residual gas remains, and therefore cooling can begin.

[0062] The magnetic resonance (MR) apparatus described above for performing the method according to the invention also falls within the scope of this invention. In an advantageous embodiment, the MR apparatus can be designed such that the vacuum pump is configured as at least two-stage and for this purpose has a turbomolecular pump and a forepump, preferably a diaphragm pump. The two pumps are preferably connected in series. Typically, only such a two-stage pump can achieve a sufficiently high vacuum.

[0063] Furthermore, the cryostat for cooling the MR magnetic coil system, which is also necessary for the MR device according to the invention and has been described above, can be improved by having the end of the fluid line connected to the cavity enter the vacuum line via a second shut-off valve in the region between the first shut-off valve and the turbomolecular pump, and the end of the fluid line connected to the pressure vessel enter the vacuum line via a third shut-off valve in the region between the turbomolecular pump and its forepump. The separate valves ensure that the helium supply device is separately located from the vacuum pump, thereby preventing the helium supply device from being pumped dry when pumping at the neck.

[0064] Control units used to perform the method according to the invention are also within the scope of the invention, such as the control units already described above.

[0065] One type of embodiment of the control unit according to the invention is particularly preferred, characterized in that it is used to measure the current pressure P in the cavity surrounding the cooling arm of the cooling head. HR A second pressure sensor is connected to the measuring unit, and the control unit is configured to open and close the second and third shut-off valves.

[0066] When the magnetic coil system is still hot, P HR Measurements are used to monitor the pressure during the initial purging of the neck tube with helium. At this time, a vacuum pump is used alternately, preferably a diaphragm pump when using a two-stage pump, to evacuate the neck tube via V2 and to fill the neck tube with helium via V1, so that as little foreign gas as possible exists in the neck tube before cooling.

[0067] P HRThe measurement is also used to monitor the presence of sufficient helium in the pressure vessel after cooling is complete, in order to monitor the degree of helium filling in the neck tube. It is also used to check the pressure gauge settings on the helium pressure vessel during operation, thereby preventing overpressure or negative pressure from occurring on the supply line.

[0068] In practice, the following improvements to these implementations have been verified, in which a connection structure from the neck tube to the vacuum pump is provided, and the control unit regulates the control from valve V2 to the vacuum pump. On one hand, the vacuum pump is used to completely purge foreign gases from the neck tube before cooling begins, in case the cryostat's temperature rise is too rapid. This prevents foreign substances from freezing, which would affect the cooling head's function. On the other hand, the vacuum pump can be used appropriately in a cold state so that, in the event of cooling head failure, the temperature rise of the cryostat can be delayed by pumping out the existing helium. The control unit adjusts the operation of V2 and the vacuum pump based on measured parameters.

[0069] Alternatively or additionally, other improvements are characterized by a connection structure from the helium supply device to the neck tube, and the control unit regulates the control of the helium supply device via a first valve V1. In this way, helium can be liquefied in a controlled manner in the event of an electrical or water failure to refill the small reserve in the neck tube. This ensures that there is always sufficient liquid helium in the neck tube to sustain operation for several hours without quenching in the event of a cooler failure.

[0070] The method variations and apparatus according to the invention are particularly preferred in the field of magnetic resonance, especially in NMR spectroscopy and in MRI equipment.

[0071] Other advantages of the invention become apparent from the description and drawings. Similarly, the features mentioned above and to be further described can be used individually or in any combination of multiple features according to the invention. The embodiments shown and described should not be construed as an exhaustive enumeration, but are exemplary in nature for the purpose of illustrating the invention. Attached Figure Description

[0072] The invention is illustrated in the accompanying drawings and described in detail with reference to the embodiments.

[0073] in:

[0074] Figure 1 A schematic vertical sectional view of one embodiment of a magnetic resonance device is shown, the device having only one valve for performing the automatic cooling method according to the invention;

[0075] Figure 2 Shown in such Figure 1 A flowchart illustrating the principle of the automatic cooling method according to the present invention in an embodiment with only one valve;

[0076] Figure 3 In such Figure 1 A schematic flowchart of the method steps according to the claims in an embodiment with only one valve;

[0077] Figure 4 A flowchart illustrating the principle process of the automatic cooling method according to the invention is shown in algorithmic form, such as the algorithm to be run in the corresponding program in the control unit, and the flowchart is used for, for example Figure 1 There is only one implementation form of valve;

[0078] Figure 5 A schematic vertical cross-sectional view of one embodiment of a magnetic resonance device with three valves for performing the automatic cooling method according to the invention is shown.

[0079] Figure 6 Shown in such Figure 5 A flowchart illustrating the principle process of the automatic cooling method according to the present invention in an embodiment having three valves;

[0080] Figure 7 Shown in such Figure 5 A schematic flowchart of the method steps according to the claims in an embodiment having three valves; and

[0081] Figure 8 A flowchart illustrating the principle process of the automatic cooling method according to the invention is shown in algorithmic form, such as the algorithm to be run in the corresponding program in the control unit, and the flowchart is used for, for example Figure 5 The implementation has three valves. Detailed Implementation

[0082] The present invention, as its core content, studies methods for special modifications to operate a magnetic resonance device 10 (“MR device”), and in particular studies autonomous cooling of superconducting magnetic systems.

[0083] Figure 1 The illustration shows a particularly simple embodiment of the magnetic resonance device 10, which has only one valve for performing the automatic cooling method according to the invention.

[0084] The MR apparatus 10 includes a vacuum container 11 with a superconducting MR magnetic coil system 12. During MR measurement operation, the MR magnetic coil system 12 is dry, i.e., without refrigerant. Cooling is achieved by a cryostat 13 connected to a compressor 13a. The cryostat 13 includes a neck 14 that extends through the outer shell 15 of the vacuum container 11 to the MR magnetic coil system 12. A cooling arm 16 of a cooling head 17 is disposed within the neck 14 of the cryostat 13. A cavity 18 is formed around the cooling arm 16. The cavity 18 is fluid-tightly sealed relative to the MR magnetic coil system 12 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.

[0085] A vacuum pump 20 is disposed outside the vacuum container 11. This vacuum pump is configured as a two-stage vacuum pump 20. Here, the vacuum pump 20 includes a turbomolecular pump 20a with a backing pump 20b (e.g., a diaphragm pump). The vacuum pump 20 is connected to the vacuum container 11 via a vacuum line 22 using a first shut-off valve 21 (shut-off valve V3).

[0086] The MR magnetic coil system 12 is equipped with a device for measuring the current temperature T on the MR magnetic coil system 12. ist Temperature sensor 23. First pressure sensor 24, connected to vacuum container 11 via vacuum line 22, measures the current pressure P in vacuum container 11. ist The control unit 40 detects the current temperature T on the MR magnetic coil system 12. ist It then compares this value with a pre-defined temperature setpoint. Furthermore, the control unit 40 also detects the current pressure P in the vacuum container 11. ist It compares this value with a pre-defined pressure setting. The control unit 40 is further configured to operate the first shut-off valve 21, the vacuum pump 20, and the compressor 13a of the cooling head 17.

[0087] The control unit 40 includes a measurement unit, a control unit, and a processor unit. A temperature sensor 23 is connected to the measurement unit and is used to measure the current temperature T on the MR magnetic coil system 12. ist Furthermore, pressure sensor 24 is connected to the measuring unit to measure the current pressure P in the vacuum container 11. istThe control unit is connected to a first shut-off valve 21, which can open and close the control unit. Furthermore, the control unit is connected to a vacuum pump 20 and a cooling head 17 (or compressor 13a), and can activate and deactivate the vacuum pump. A processor unit is located 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 set parameters. The processor unit processes this data and uses it to control the cooling head 17, the vacuum pump 20, and the shut-off valve 21.

[0088] The current pressure P in cavity 18 can be measured via the second pressure sensor 25. HR The second pressure sensor is connected to the connection structure 28 of the cavity 18 leading from the helium supply device 29 to the cryostat 13. The second pressure sensor 25 is also connected to the measurement unit of the processor unit.

[0089] For implementations with only one valve, in Figure 2 The flowchart illustrates the principle process of the cooling method according to the present invention.

[0090] Example

[0091] In the implementation plan, the autonomous cooling process may include the following steps:

[0092] 1. Start the MR equipment. In this operating state, shut-off valve V3 is closed and the vacuum pump is stopped.

[0093] The helium supply unit is directly connected to the neck tube. It liquefies gaseous helium, and the liquid helium cools the MR magnet system. Liquefaction continues until the system reaches thermodynamic equilibrium.

[0094] 2. The temperature sensor measures the current temperature T on the MR magnetic coil system. ist .

[0095] 3. Set the temperature T ist The temperature is sent to the control unit, and here in the processor unit, the temperature is compared with a predefined temperature setpoint T1. soll In comparison, the temperature setting mentioned here is 8K. If T ist ≥T1 soll If the control unit is activated, it will open shut-off valve V3 and activate the vacuum pump.

[0096] When, for example, the compressor fails and cooling of the MR coil system is also achieved, a temperature rise occurs. The heat input to the MR coil system from the ambient environment increases. However, the MR coil system does not heat up immediately. First, liquid helium evaporates, thereby cooling the MR coil system. The evaporated helium is discharged through the pressure relief valve. However, if the compressor failure is prolonged, helium may completely evaporate, causing the MR coil system to quench and heat up. Due to this heating, gases are released from the MR coil system in the vacuum container. These gases degrade the vacuum, which negatively impacts insulation. There is a risk of excessively rapid and uncontrolled heating. To prevent this, the control unit activates in advance to open the shut-off valve V3 and activate the vacuum pump, thereby maintaining the vacuum in the vacuum container for as long as possible and reducing the heat input to the MR coil system, thus suppressing uncontrolled heating of the MR coil system.

[0097] 4. The pressure sensor measures the current pressure P of the vacuum container. ist .

[0098] 5. Apply pressure P ist It is sent to the control unit, where it is compared with the predefined pressure setpoint P1 in the processor unit. soll In comparison, the pressure setting value described here is 10. -3 mbar. If P ist <P1 soll If the condition is met, the control unit is activated. The control unit activates the cooling head to cool the cooling arm.

[0099] Through pressure setpoint P1 soll This ensures that a sufficient vacuum is maintained in the vacuum chamber, thereby reducing the heat input to the MR magnetic coil system. If this value is achieved, the cooling head is cooled again to bring the MR equipment back to normal operation.

[0100] 6. The temperature sensor measures the current temperature T on the MR magnetic coil system. ist .

[0101] 7. Set the temperature T ist The data is sent to the control unit and then processed in the processor unit with the predefined temperature setpoint T1. soll In comparison. If T ist <T1 soll If the condition is met, the control unit will start. The control unit will close the shut-off valve V3 and stop the vacuum pump.

[0102] 8. The temperature sensor continues to measure the current temperature T on the MR magnetic coil system. ist Temperature T ist The data is sent to the control unit and then processed in the processor unit with the predefined temperature setpoint T2.soll In comparison, the temperature setting mentioned here is 4.2K. If T ist ≤T2 soll If this is the case, the control unit will activate. The control unit will then instruct the cooling head to maintain this temperature.

[0103] 9. Supply gaseous helium to the neck tube again.

[0104] Temperature T ist This is sufficient to liquefy gaseous helium. The liquid helium cools the MR magnetic coil system and liquefies it continuously, keeping the system in thermodynamic equilibrium.

[0105] Figure 3 A schematic flowchart illustrating the method steps according to the claims is shown for an embodiment having only one valve.

[0106] Start: To start the MR device.

[0107] a1: Measure the current temperature T of the MR magnetic coil system. ist And compare it with a first temperature setpoint T1 that can be predetermined. soll In contrast, the vacuum container should be pumped out starting from the first temperature setpoint.

[0108] a2: If T ist >T1 soll This activates the vacuum pump located outside the vacuum container and opens the first shut-off valve in the pipeline from the vacuum pump to the vacuum container.

[0109] b1: Measure the current pressure P in the vacuum container ist And compare it with the pre-defined first pressure setting value P1 soll In comparison, under the first pressure setting, the MR electromagnetic coil system should be cooled to a low temperature.

[0110] b2: If P ist <P1 soll Then the cooling head is activated to cool the cooling arm.

[0111] c1: Measure the current temperature T on the MR magnetic coil system. ist And compare it with the first temperature setpoint T1 soll In comparison.

[0112] c2: If T ist <T1 soll If the first shut-off valve is closed, the vacuum pump will also be shut off.

[0113] d1: Measure the current temperature T on the MR magnetic coil system. ist And compare it with the second temperature setpoint T2 sollIn comparison, at the second temperature setpoint, the operating temperature of the MR magnetic coil system for MR measurement is reached. The second temperature setpoint T2 is maintained. soll .

[0114] e: Supply helium into the neck tube and liquefy it.

[0115] exist Figure 4 The implementation with only one valve is shown as a flowchart in the form of an algorithm that should be run as a corresponding program in the control unit, illustrating the principle of the cooling method according to the invention.

[0116] The algorithm can be divided into the following steps:

[0117] S1: Start control unit.

[0118] S2: The temperature sensor connected to the measurement unit in the MR magnetic coil system measures the current temperature T. ist .

[0119] S3: In the processor unit, the temperature T ist AND value T1 soll Compare and check if T ist ≥T1 soll If the check result is negative, the algorithm continues in S7. If the check result is positive, the control unit activates the vacuum pump and opens the shut-off valve V3.

[0120] S4: The control unit activates the vacuum pump and opens the shut-off valve V3.

[0121] S5: Pressure sensor for vacuum containers connected to the measuring unit to measure the current pressure P. ist .

[0122] S6: In the processor unit, the pressure P ist With value P1 soll Compare and check if P ist <P1 soll If the check result is negative, then remeasure the pressure P. ist (And the algorithm continues in S5). If the check result is positive, the control unit activates the cooling head.

[0123] S7: Control unit activates cooling head.

[0124] S8: The control unit may shut off the shut-off valve V3 and stop the vacuum pump if necessary.

[0125] S9: The temperature sensor connected to the measurement unit of the MR magnetic coil system measures the current temperature T. ist .

[0126] S10: In the processor unit, the temperature T ist AND value T2 soll Compare and check if T ist ≥T2 soll If the check results in a negative result, the algorithm continues in S3. If the check results in a positive result, the control unit indicates with a signal that the cooling head should maintain temperature T2. soll .

[0127] S11: The control unit instructs the cooling head to maintain a temperature of T2. soll .

[0128] Figure 5 A particularly simple embodiment of a magnetic resonance apparatus 10 (MR apparatus) with three valves is schematically shown for performing the automatic cooling method according to the invention.

[0129] The MR apparatus 10 includes a vacuum container 11 with a superconducting MR magnetic coil system 12. During MR measurement operation, the MR magnetic coil system 12 is dry, i.e., without refrigerant. Cooling is achieved by a cryostat 13 connected to a compressor 13a. The cryostat 13 includes a neck 14 that extends through the outer shell 15 of the vacuum container 11 to the MR magnetic coil system 12. A cooling arm 16 of a cooling head 17 is disposed within the neck 14 of the cryostat 13. A cavity 18 is formed around the cooling arm 16. The cavity 18 is fluid-tightly sealed relative to the MR magnetic coil system 12 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.

[0130] A vacuum pump 20 is disposed 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 backing pump 20b (e.g., a diaphragm pump). The vacuum pump 20 is connected to the vacuum container 11 via a vacuum line 22 using a first shut-off valve 21 (shut-off valve V3). Furthermore, the vacuum pump 20 is connected to the neck tube 14 via a connecting structure 26 using a second shut-off valve 27 (shut-off valve V2).

[0131] The MR magnetic coil system 12 is equipped with a device for measuring the current temperature T on the MR magnetic coil system 12. ist Temperature sensor 23. First pressure sensor 24, connected to vacuum container 11 via vacuum line 22, measures the current pressure P in vacuum container 11. ist The current pressure P in the neck tube is measured by a second pressure sensor 25 connected to the neck tube 14 via the connection structure 26. HR The control unit 40 (not shown here) detects the current temperature T on the MR magnetic coil system 12. istIt then compares this value with a pre-defined temperature setpoint. Furthermore, the control unit 40 detects the current pressure P in the vacuum container 11. ist It is compared with a pre-defined pressure setpoint. The control unit 40 is also configured to operate the first shut-off valve 21, the vacuum pump 20, and the compressor 13a of the cooling head 17.

[0132] The control unit 40 includes a measurement unit, a control unit, and a processor unit. A temperature sensor 23 is connected to the measurement unit and is used to measure the current temperature T on the MR magnetic coil system 12. ist Furthermore, a first pressure sensor 24 is connected to the measuring unit, and the current pressure P in the vacuum container 11 is measured using the first pressure sensor. ist Similarly, the second pressure sensor 25 is also connected to the measuring unit, which measures the current pressure P in the neck tube 14. HR The control unit is connected to the first shut-off valve 21, the second shut-off valve 27, and the third shut-off valve 30 (shut-off valve V1), and can open and close these shut-off valves. Shut-off valve 30 is integrated into a connection structure 28 that connects the helium supply device 29 to the neck tube 14. Furthermore, the control unit is connected to the vacuum pump 20 and, via the compressor 13a, to the cooling head 17, and can activate and deactivate the vacuum pump and the cooling head. A processor unit is located between the measurement unit and the control unit. The processor unit compares the parameters detected by the temperature sensor 23, pressure sensor 24, and pressure sensor 25 with set parameters. The processor unit processes this data and uses it to control the cooling head 17, the vacuum pump 20, and the shut-off valves 21, 27, and 30.

[0133] exist Figure 6 The flowchart illustrates the principle of the cooling method according to the invention for an embodiment with three valves.

[0134] Example:

[0135] The process of the autonomous cooling method may include the following steps in some implementation schemes:

[0136] 1'. Start the MR equipment. In this operating state, shut-off valves V1, V2, and V3 are closed, and the vacuum pump is stopped.

[0137] The helium supply unit is connected to the neck tube via a shut-off valve V1. This liquefies the gaseous helium, and the liquid helium cools the MR magnet assembly. Liquefaction continues until the system reaches thermodynamic equilibrium.

[0138] 2'. The temperature sensor measures the current temperature T on the MR magnetic coil system. ist .

[0139] 3'. Set the temperature T ist The data is sent to the control unit and then processed in the processor unit with the predefined temperature setpoint T1. soll In comparison, the temperature setting mentioned here is 8K. If T ist ≥T1 soll If the control unit is activated, it will open shut-off valve V3 and activate the vacuum pump.

[0140] 3.1'. Simultaneously, the processor unit will control the temperature T ist Compared with the pre-defined temperature setpoint T3 soll In comparison, the temperature setting here is 280K. If T ist >T3 soll If the control unit is activated, it will take effect. The control unit will open the shut-off valve V2 and activate the vacuum pump.

[0141] When, for example, the compressor fails and consequently the cooling of the MR coil system also fails, a temperature rise occurs. The heat input from the environment to the MR coil system increases. Of course, the MR coil system will not heat up immediately. When the temperature exceeds the setpoint T3... soll When the compressor fails for an extended period, the control unit activates. It opens shut-off valve V2 and pumps out helium, thereby actively cooling the MR coil system. However, if the compressor fails for an extended period, the helium may completely evaporate, causing the MR coil system to quench and overheat. This overheating releases gas from the MR coil system into the vacuum container. This gas degrades the vacuum, negatively impacting insulation. There is a risk of excessively rapid and uncontrolled overheating. To prevent this, the control unit activates earlier to open shut-off valve V3 and activate the vacuum pump, thereby maintaining the vacuum in the container for as long as possible and reducing the heat input to the MR coil system, thus suppressing uncontrolled overheating.

[0142] 4'. The pressure sensor measures the current pressure P of the vacuum container. ist .

[0143] 5'. Apply pressure P ist It is sent to the control unit, where it is compared with the predefined pressure setpoint P1 in the processor unit. soll In comparison, the pressure setting value described here is 10. -3 mbar. If P ist <P1 soll If the condition is met, the control unit is activated. The control unit activates the cooling head to cool the cooling arm.

[0144] Through pressure setpoint P1 sollThis ensures that a sufficient vacuum exists within the vacuum chamber, thereby reducing the heat input to the MR magnetic coil system. If this value is achieved, the cooling head is cooled again to bring the MR equipment back into normal operation.

[0145] 6'. The temperature sensor measures the current temperature T on the MR magnetic coil system. ist .

[0146] 7'. Set the temperature T ist The data is sent to the control unit and then processed in the processor unit with the predefined temperature setpoint T1. soll In comparison. If T ist <T1 soll If the condition is met, the control unit will start. The control unit will close the shut-off valve V3 and stop the vacuum pump.

[0147] 8'. The temperature sensor continues to measure the current temperature T on the MR magnetic coil system. ist Temperature T ist The data is sent to the control unit and then processed in the processor unit with the predefined temperature setpoint T2. soll In comparison, the temperature setting mentioned here is 4.2K. If T ist ≤T2 soll If this is the case, the control unit will activate. The control unit will then instruct the cooling head to maintain this temperature.

[0148] 9'. Close shut-off valve V2 and open shut-off valve V1 to supply gaseous helium to the neck tube again.

[0149] Temperature T ist This is sufficient to liquefy gaseous helium. Liquid helium cools the MR magnet device and continues to liquefy it until the system reaches thermodynamic equilibrium.

[0150] 10'. Alternatively, in the event of a cooling head failure, the control unit can reactivate the vacuum pump and open the shut-off valve V2.

[0151] exist Figure 7 The embodiment with three valves is shown in a schematic flowchart illustrating the method steps according to the claims.

[0152] Start: The MR equipment has started operating.

[0153] a1 / a3: Measures the current temperature T of the MR magnetic coil system. ist And compare it with a first temperature setpoint T1 that can be predetermined. soll In contrast, the vacuum container should be pumped out starting from the first temperature setpoint. Alternatively, the current temperature T can be... ist With the pre-defined third temperature setpoint T3 soll In comparison.

[0154] a4: If T ist >T3 soll This activates the vacuum pump located outside the vacuum container and opens the second shut-off valve V2 in the vacuum line leading from the vacuum pump to the neck tube.

[0155] a2: If T ist >T1 soll This activates the vacuum pump located outside the vacuum container and opens the first shut-off valve in the pipeline leading from the vacuum pump to the vacuum container.

[0156] b1: Measure the current pressure P in the vacuum container ist And compare it with a pre-defined first pressure setting value P1 soll In comparison, under the first pressure setting, the MR electromagnetic coil system should be cooled to a low temperature.

[0157] b2: If P ist <P1 soll Then the cooling head is activated to cool the cooling arm.

[0158] c1: Measure the current temperature T on the MR magnetic coil system. ist And compare it with the first temperature setpoint T1 soll In comparison.

[0159] c2: If T ist <T1 soll If the first shut-off valve is closed, the vacuum pump will also be shut off.

[0160] d1: Measure the current temperature T on the MR magnetic coil system. ist And compare it with the second temperature setpoint T2 soll In comparison, at the second temperature setpoint, the operating temperature of the MR magnetic coil system for MR measurements was achieved. The second temperature setpoint T2 was maintained. soll .

[0161] e: Supply helium into the neck tube and liquefy it.

[0162] d2: In the event of cooling head failure, the liquid helium in the neck tube is pumped by a vacuum pump to cool the MR magnetic coil system.

[0163] exist Figure 8 The principle of the cooling method according to the invention, for an implementation with three valves, is illustrated as a flowchart in the control unit, showing the algorithm that should be run by the corresponding program.

[0164] The algorithm can be divided into the following steps:

[0165] S'1: Start control unit.

[0166] S'2: The temperature sensor connected to the measurement unit in the MR magnetic coil system measures the current temperature T. ist .

[0167] S'3: In the processor unit, the temperature T ist AND value T1 soll Compare and check if T ist ≥T1 soll If the check result is negative, the algorithm continues in S7'. If the check result is positive, the control unit activates the vacuum pump and opens the shut-off valve V3.

[0168] S'4: The control unit activates the vacuum pump and opens the shut-off valve V3.

[0169] S'4.1: The temperature sensor connected to the measurement unit of the MR magnetic coil system measures the current temperature T. ist .

[0170] S'4.2: In the processor unit, the temperature T ist AND value T3 soll Compare and check if T ist >T3 soll If the check result is positive, the control unit activates the vacuum pump and opens the shut-off valve V2.

[0171] S5': A pressure sensor for the vacuum container connected to the measuring unit measures the current pressure P. ist .

[0172] S6': In the processor unit, the pressure P ist With value P1 soll Compare and check if P ist <P1 soll If the check result is negative, then remeasure the pressure P. ist (And the algorithm continues in S5'). If the check result is positive, the control unit activates the cooling head.

[0173] S7': Control unit activates the cooling head.

[0174] S8': If necessary, the control unit closes shut-off valves V3 and V2 and stops the vacuum pump.

[0175] S9': The temperature sensor connected to the measurement unit in the MR magnetic coil system measures the current temperature T. ist .

[0176] S10': In the processor unit, the temperature T ist AND value T2 soll Compare and check if Tist ≥T2 soll If the check result is negative, the algorithm continues in S3'. If the check result is positive, the algorithm continues in S11'.

[0177] S11': Processor unit check, whether it is in normal operation, i.e., whether T2 is present. soll =OK. If the check result is positive, the algorithm continues in S12'. If the check result is negative, the algorithm continues in S13'.

[0178] S12': The control unit opens valve V1 and introduces gaseous helium into the neck tube and liquefies it.

[0179] S13': The control unit activates the vacuum pump and opens the shut-off valve V2.

[0180] List of reference numerals

[0181] 10. Magnetic Resonance (MR) Equipment

[0182] 11 Vacuum Container

[0183] 12 Magnetic Coil System

[0184] 13 Low-temperature thermostat

[0185] 13a compressor

[0186] 14. Cervical canal

[0187] 15. Outer shell

[0188] 16 Cooling Arms

[0189] 17 Cooling Head

[0190] 18. Cavity

[0191] 19 cryogenic fluids

[0192] 20 Vacuum Pumps

[0193] 20a turbomolecular pump

[0194] 20b backing pump

[0195] 21. Shut-off valve (V3)

[0196] 22 Vacuum lines

[0197] 23 Temperature sensor

[0198] 24 First pressure sensor

[0199] 25 Second pressure sensor

[0200] 26 Connecting lines (from neck tube to vacuum pump)

[0201] 27. Shut-off valve (V2)

[0202] 28. Connecting pipeline (from helium supply unit to neck tube)

[0203] 29 Helium supply unit

[0204] 30. Shut-off valve (V1)

[0205] 40 Control Unit

[0206] List of Literature

[0207] Publications considered for assessing patentability:

[0208] [1]DE 10 2016 218 000B3≈WO 2018 / 054648 A1≈EP 3 296 669B1≈CN107845474 B≈JP 6338755 B≈US 10 101 420B2

[0209] [2]DE 20 2017 001 501U1

[0210] [3]EP 3 454 071A1

[0211] [4]US 8 729 894B2

[0212] [5]US 2006 0225433A1

[0213] [6]DE 10 2014 218 773B4≈CN 105501679 B≈GB 2532322B≈US 10 203 067B2

[0214] [7]DE 10 2015 215 919B4≈GB 2542667 B≈US 10 203 068B2.

Claims

1. A method for operating a magnetic resonance (MR) device (10), the MR device having a refrigerant-free superconducting MR magnetic coil system (12) disposed in a vacuum container (11) and a cryostat (13) for cooling the MR magnetic coil system (12), the cryostat including a neck tube (14) extending through a shell (15) of the vacuum container (11) to the MR magnetic coil system (12), a cooling arm (16) of a cooling head (17) being at least partially disposed in the neck tube (14), forming a closed cavity (18) around the cooling arm (16), the cavity being fluid-tightly sealed relative to the MR magnetic coil system (12) to be cooled, and being at least partially filled with a cryogenic fluid (19) during normal operation of the MR device (10). Its features are, The method includes the following steps: In order to autonomously cool the MR magnetic coil system (12) to a low temperature at which the superconducting MR magnetic coil system (12) can be charged by current: (a1) Measure the current temperature T on the MR magnetic coil system (12). ist and T ist With the first temperature setpoint T1 that can be predetermined soll In contrast, the vacuum container (11) should be pumped out starting from the first temperature set value; (a2) If T ist >T1 soll Then the vacuum pump (20) located outside the vacuum container (11) is activated, and the first shut-off valve (21) in the vacuum line (22) from the vacuum pump (20) to the vacuum container (11) is opened. (b1) Measure the current pressure P in the vacuum container (11). ist and P ist With the pre-defined first pressure setpoint P1 soll In comparison, under the first pressure setting, the MR magnetic coil system (12) should be cooled to a low temperature; (b2) If P ist <P1 soll Activate the cooling head (17) to cool the cooling arm (16). (c1) Measure the current temperature T on the MR magnetic coil system (12). ist and T ist Compared with the first temperature setpoint T1 soll In comparison; (c2) If T ist <T1 soll , shut off the first shut-off valve (21) and turn off the vacuum pump (20); (d1) Measure the current temperature T on the MR magnetic coil system (12). ist and T ist With the pre-defined second temperature setpoint T2 soll Compare and maintain the second temperature setpoint T2 soll At the second temperature setpoint, the operating temperature of the MR magnetic coil system (12) for MR measurement is reached. The supply line (26) to the neck tube (14) is connected to the vacuum pump (20) via another valve V2 (27), and the neck tube (14) is emptied using the following steps: (a3) Measure the current temperature T on the MR magnetic coil system (12). ist and T ist With the pre-defined third temperature setpoint T3 soll In contrast, the neck tube (14) should be pumped out starting from the third temperature setting value; and (a4) If T ist >T3 soll Then the vacuum pump (20) is activated and the second shut-off valve V2 (27) in the supply line (26) leading from the vacuum pump (20) to the neck tube (14) is opened. Before activating the cooling head (17) to cool the cooling arm (16), steps (a3) ​​and (a4) are performed, and after step (a4), the vacuum pump (20) is turned off, and gaseous helium is supplied to the vacuum-evacuated neck tube (14) after a short waiting period.

2. The method according to claim 1, characterized in that, The neck tube (14) is connected to the helium supply device (29) via the first valve V1 (30), and in step (e), helium is supplied to the neck tube (14) and liquefied.

3. The method according to claim 1 or 2, characterized in that, In the event of failure of the cooling head (17), in step (d2), liquid helium in the neck tube (14) is pumped out using a vacuum pump (20) to cool the MR magnetic coil system (12).

4. The method according to claim 1 or 2, characterized in that, The temperature setpoint T1 can be preset. soll T2 soll and T3s oll And the pre-defined pressure setpoint P1 soll Selected from the following value range: 5K ≤ T1 soll ≤ 20K; 3K ≤ T2 soll ≤ 5K; 250K ≤ T3 soll ≤300K; 10 -4 end ≤ P1 soll ≤ 10 -1 finished.

5. The method according to claim 4, characterized in that, The temperature setpoint T1 can be preset. soll T2 soll and T3s oll And the pre-defined pressure setpoint P1 soll It has the following values: T1 soll Approximately 8K; T2 soll Approximately 4.2K; T3 soll Approximately 280K; P1 soll Approximately 10 -3 mbar.

6. A magnetic resonance (MR) apparatus (10) for performing the method according to any one of claims 1 to 5, the magnetic resonance apparatus having an MR magnetic coil system (12) disposed in a vacuum container (11) and having a refrigerant-free superconducting MR measurement operation and a cryostat (13) for cooling the MR magnetic coil system (12). The cryostat includes a neck tube (14) that extends through the outer shell (15) of the vacuum container (11) to the MR magnetic coil system (12). A cooling arm (16) of a cooling head (17) is at least partially disposed within the neck tube (14), forming a closed cavity (18) around the cooling arm (16). This cavity is fluid-tightly sealed relative to the MR magnetic coil system (12) to be cooled and is at least partially filled with a cryogenic fluid (19) during normal operation of the MR device (10). A vacuum pump (20) and a first shut-off valve (21) are installed outside the vacuum container (11) in the vacuum line (22) leading from the vacuum pump (20) to the vacuum container (11). A current temperature T is provided for measuring the MR magnetic coil system (12). ist Temperature sensor (23) and for measuring the current pressure P in vacuum container (11) ist The first pressure sensor (24). The control unit (40) is configured to detect the current temperature T on the MR magnetic coil system (12). ist It is compared with a pre-defined temperature setpoint to detect the current pressure P in the vacuum container (11). ist It is compared with a pre-defined pressure setting and used to control the first shut-off valve (21), vacuum pump (20) and cooling head (17).

7. The MR device according to claim 6, characterized in that, The vacuum pump (20) is configured to be at least two stages and for this purpose has a turbomolecular pump (20a) and a forepump (20b).

8. The MR device according to claim 7, characterized in that, The forepump (20b) is a diaphragm pump.

9. A control unit (40) for performing the method according to any one of claims 1 to 5, the control unit being used in an MR device (10), the control unit (40) being configured to detect a current temperature T on the MR magnetic coil system (12). ist And compare it with a pre-defined temperature setpoint and the current pressure P in the vacuum container (11) for detection. ist And compare it with a pre-defined pressure setting value, characterized in that, The control unit (40) has a measuring unit connected to which a method for measuring the current temperature T on the MR magnetic coil system (12) is connected. ist Temperature sensor (23) and for measuring the current pressure P in vacuum container (11) ist Pressure sensor (24). The control unit (40) includes 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 cooling head (17). The control unit (40) includes a processor unit configured as an interface between the measurement unit and the control unit for comparing detected sensor parameters with set parameters and for processing data in order to control the cooling head (17), the vacuum pump (20) and the shut-off valve (21).

10. The control unit according to claim 9, characterized in that, Used to measure the current pressure P in the cavity (18) of the cooling arm (16) surrounding the cooling head (17). HR The second pressure sensor (25) is connected to the measuring unit, and the control unit is configured to open and close the second and third shut-off valves.

11. The control unit according to claim 10, characterized in that, A supply line (26) is provided from the neck tube (14) to the vacuum pump (20), and the control unit (40) regulates the control from valve V2 (27) to the vacuum pump (20).

12. The control unit according to claim 10 or 11, characterized in that, A connection structure (28) is provided 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 first valve V1 (30).

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