Shielding coil and quench protection combined design structure and method for magnet system

Abstract

The invention discloses a magnet system shielding coil and quench protection combined design structure, which comprises a superconducting magnet main coil and a shielding coil, a superconducting magnet main coil loop is provided with a main magnet coil group and a main coil switch, two ends of the main coil switch are provided with main coil loop power-up ports, the main magnet coil group comprises first to nth main magnet coils, and the shielding coil is arranged between the first to nth main magnet coils. Two ends of the switch heater are connected with main magnet coils as heating current sources; the shielding coil loop is provided with a shielding coil group and a shielding coil switch, the heater group is connected with the shielding coil group in parallel, the heater group is first to nth resistance heaters corresponding to the heating main magnet coil, the shielding coil group is first to nth shielding coils, and the two ends of the shielding coil switch are provided with shielding coil loop power-up ports. The switch heater is used for heating the shielding coil switch, a corresponding design method is generated through the structure, and the shielding coil assembly has multiple functions and serves as a current source of a quench protection loop while shielding external field changes.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of magnet systems, and relates to a magnet system shielding coil and quench protection combined design structure and method. BACKGROUND

[0002] When an MRI superconducting magnet is running, there are high requirements for the stability of the magnetic field and the uniformity of the uniform region. Changes in the external magnetic field will cause changes in the current of the superconducting magnet internal solenoid, thereby causing changes in the magnetic field value, which will affect the imaging quality. Due to the inevitable existence of changes in the external magnetic field (such as the geomagnetic field), when designing the main magnet coil of the MRI superconducting magnet, the design of the shielding coil (shielding coil) is also completed at the same time, so as to reduce the influence of the external environment on the stability of the magnetic field and the uniformity.

[0003] The existing shielding coil design optimization objective functions mainly include shielding coefficient, magnetic field uniformity and wire length parameters, and the shielding coil is independent of the quench protection. The shielding coefficient and wire length are used as the objective functions by Huazhong University of Science and Technology; the shielding coefficient is used as the objective function by the Chinese Academy of Engineering Research; and the shielding coefficient is used as the objective function by Xingaoyi Medical Equipment Co., Ltd.

[0004] The quench protection system includes active protection and passive protection. The active protection detects the voltage of the bridge through the detection coil, and when the voltage is higher than the threshold value, the active heating coil accelerates the quench propagation. The passive protection technology basically uses diodes and resistors in series and parallel for protection. The common protection circuit of the MRI superconducting magnet connects the heater in parallel with a certain main magnet coil, and when quench occurs, a voltage is generated across the coil, and the heater heats the main coil. Shanghai United Imaging Medical Technology Co., Ltd. designs a quench protection method with an internal energy storage element, which additionally increases an additional circuit system, and does not consider the influence of the additional current generated by the inductive voltage on the quench heater during the quench process.

[0005] The MRI superconducting magnet system is a multi-solenoid system, and there is no thermal link or only a weak thermal link between the solenoids. In order to ensure that the internal energy storage can be uniformly dissipated on each solenoid when quench occurs, so as not to burn out the coil, a heater is generally used to heat the remaining non-quench coil during quench. Most of the heaters on the market choose to collect the voltage of the main coil for driving. Due to quench, a very high voltage may be generated across the coil, which can easily burn out the heater, thereby causing the superconducting magnet to lose the protection system. SUMMARY

[0006] The application aims to provide a magnet system shielding coil and quench protection combined design structure and method, which decouples the heater from the main loop and forms a protection loop with the shielding coil, limits the current size of the heater in the quench process through the shielding coil as the current source design of the quench protection loop, so as to ensure that the heater will not be burned out, and also avoids the high voltage of the main coil quench from burning out the heater, greatly improves the stability and safety of the heater.

[0007] The technical scheme adopted by the application is as follows: A magnet system shielding coil and quench protection combined design structure, which comprises a superconducting magnet main coil and a shielding coil, a main magnet coil group and a main coil switch are arranged on the main magnet coil loop, a main coil loop power port is arranged at both ends of the main coil switch, the main magnet coil group is a first main magnet coil, a second main magnet coil,..., and an n-th main magnet coil arranged in sequence, a switch heater is connected between the first main magnet coil and the n-th main magnet coil, and one or more main magnet coils are used as a heating current source; a shielding coil group and a shielding coil switch are arranged on the shielding coil loop, a heater group is arranged in parallel with the shielding coil group, the heater group is a first electric resistance heater, a second electric resistance heater,..., and an n-th electric resistance heater which are respectively attached to and heated by the first to n-th main magnet coils, the shielding coil group is a corresponding first shielding coil, a second shielding coil,..., and an n-th shielding coil, a shielding coil loop power port is arranged at both ends of the shielding coil switch, and the switch heater is close to the shielding coil switch for heating the shielding coil switch.

[0008] Further, in the initial stage, energy is stored in the shielding coil group through the shielding coil loop power port, and the heater group is energized for use when quenching.

[0009] Further, in the normal use stage, the two loops are: Main magnet coil loop: first main magnet coil-second main magnet coil-...-n-th main magnet coil-main coil switch-first main magnet coil, original excitation current I 10 exists; Shielding coil loop: first shielding coil-second shielding coil-...-n-th shielding coil-shielding coil switch-first shielding coil, original energy storage current I 20 exists; When the main loop has a quench point, the switch heater heats the shield coil switch, forcing the shield coil switch to open and become a resistive element, thereby forcing a portion of I2 to flow into the first resistor heater-second resistor heater-…-nth resistor heater loop, at which time the first resistor heater, the second resistor heater, …, and the nth resistor heater generate heat to heat the corresponding main magnet coil, accelerate the quench propagation of the main magnet, and thereby make the coil energy storage uniformly dissipate on each coil, sequentially achieving the effect of protecting the superconducting magnet.

[0010] Further, the number of main magnet coils connected across the switch heater (EH) is matched with the heating required.

[0011] A magnet system shield coil and quench protection combined design method, based on the above-mentioned magnet system shield coil and quench protection combined design structure, is adapted to the following steps: S1, simplify the circuit: when the main magnet quenches, the circuit degenerates into: LOOP1: the first inductor is the equivalent inductor element of the shield coil group, the first resistor is the equivalent resistor of the heater group and the shield coil switch in parallel, and the second resistor is the equivalent resistor of the shield coil group; LOOP2: the second inductor is the equivalent inductor of the main magnet coil group, the third resistor is the equivalent resistor of the main magnet coil group, and the fourth resistor is the equivalent resistor of the main magnet switch; S2, calculate the mutual inductance value; the first inductor and the second inductor inevitably have magnetic coupling, and the mutual inductance value is set as M. During the quenching process, the shield coil loop will generate an induced electromotive force ; wherein, is the current in loop LOOP2, is the incremental current generated by the inductor in loop LOOP2; thereby causing the current in loop LOOP1 to be ； wherein, is the incremental current generated by the inductor in loop LOOP1, is the original energy storage current; to ensure that the heater does not burn out during the quenching process, the current in loop LOOP1 needs to meet the condition , then the mutual inductance M should meet the condition: ; wherein, a is the current limiting current, b is a constant related to the quenching process, R1 is the first resistor, and R2 is the second resistor; S3, optimizing mutual inductance value: the shield coil is combined with the quench protection circuit, first, to prevent the shield coil from generating too high electromotive force in the quench process, burning the heater and the shield coil switch, the mutual inductance between the main magnet and the shield coil is taken as one of the objective functions of the shield coil optimization design, second, under the quench protection circuit, the mutual inductance value needs to meet the requirement, and the shield coil design objective function is obtained: ;

[0012] Wherein, S is a shielding factor, ppm is the magnetic field uniformity after the shield coil and the main magnet coil are superposed, M is the mutual inductance value, W1 / W2 / W3 is the weight factor; According to the shield coil optimization calculation result and the constraint condition, the quench protection circuit is designed: .

[0013] Further, in step S1, when the main magnet quenches, the current generated in the heater heats the shield coil switch, forcing the shield coil switch to open and become a resistive element, at this time, I2 part flows into the first resistor heater-second resistor heater-third resistor heater-fourth resistor heater, heating the remaining main magnet coil which has not quenched, accelerating the quench.

[0014] As described above, due to the adoption of the above technical scheme, the beneficial effects of the present application are: 1. The present scheme decouples the heater in the main circuit and forms a protection circuit with the shield coil, by designing the shield coil as a current source of the quench protection circuit, the current size of the heater in the quench process is limited, so that the heater is not burned out, and the high voltage caused by the main coil quenching is also avoided to burn the heater, which greatly improves the stability and safety of the heater.

[0015] 2. The shield coil group has multiple functions, and changes the shielding of the external field while also serving as a current source of the quench protection circuit.

[0016] 3. In the present method, the quench protection is coupled with the shield coil, considering the shielding coefficient, magnetic field uniformity, and related parameters of the quench protection system, the mutual inductance value between the shield coil and the main magnet coil needs to meet certain requirements to prevent the superconducting switch or the heater from being burned out in the quench process, the circuit after quenching is simplified, and the mutual inductance value and the inequality relationship of the quench protection resistor are calculated to calculate the heater resistance or mutual inductance limit. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor based on the drawings. Figure 1 is a position diagram of a magnet system shielding coil and quench protection combined design structure of the present application.

[0018] Figure 2 is a circuit diagram of a magnet system shielding coil and quench protection combined design structure of the present application.

[0019] Figure 3 is a protection circuit diagram after the quench of a magnet system shielding coil and quench protection combined design method of the present application.

[0020] Figure 4 is a corresponding initial shielding coil design parameter diagram in embodiment 2.

[0021] The marks in the figure are: main coil switch S1, first main magnet coil C1, second main magnet coil C2, third main magnet coil C3, fourth main magnet coil C4, shielding coil switch S2, first resistance heater H1, second resistance heater H2, third resistance heater H3, fourth resistance heater H4, switch heater EH, first shielding coil EC1, second shielding coil EC2, third shielding coil EC3, fourth shielding coil EC4. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present application more clear and explicit, the following will further describe the present application in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application, that is, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0024] It is to be understood that the terms "first" and "second", and the like, merely denote different ones of the same entity or action, without necessarily requiring or implying any actual relationship or order between such entities or actions. Also, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0025] The features and advantages of the present application will be further described in the following detailed description of the embodiments.

[0026] Embodiment 1:

[0027] A magnet system shielding coil and quench protection combined design structure, which comprises a superconducting magnet main coil and a shielding coil, a main magnet coil group is arranged on the main magnet coil loop, a main coil switch S1 is arranged, main coil loop power supply ports V3, V4 are arranged at both ends of the main coil switch S1, the main magnet coil group is a first main magnet coil C1, a second main magnet coil C2,..., and an n-th main magnet coil Cn arranged in sequence, a switch heater EH is connected between the first main magnet coil C1 and the n-th main magnet coil Cn at both ends, and the number of more than one main magnet coil at both ends is used as a heating current source, that is, the number of main magnet coils at both ends is matched as a current source, and the switch heater EH cannot be connected by short circuit at both ends; a shielding coil group and a shielding coil switch S2 are arranged on the shielding coil loop, a heater group is arranged in parallel with the shielding coil group, the heater group is a first resistance heater H1, a second resistance heater H2,..., and an n-th resistance heater Hn which are respectively attached to and heated by the first to n-th main magnet coils, the shielding coil group is a corresponding first shielding coil EC1, a second shielding coil EC2,..., and an n-th shielding coil ECn, shielding coil loop power supply ports V1, V2 are arranged at both ends of the shielding coil switch S2, the switch heater EH is close to the shielding coil switch S2 for heating the shielding coil switch S2, the number of main magnet coils connected at both ends of the switch heater EH is matched with the heating required, and short circuit or burning is needed to be avoided, the matching refers to the heating required power or energy, and the heating time and the like need to be considered, the resistance of the switch heater EH and the number of main magnet coils are adjusted according to the actual demand, and the number of main magnet coils can be flexibly adjusted. In actual use, n is a natural number greater than or equal to 1, of course, this is only a theoretical design, based on the existing actual design, n is generally selected as a natural number between 4 and 9, and the commonly used number of coils is 8 or 9 coils.

[0028] The initial stage stores energy in the shielding coil group through the shielding coil loop power supply ports V1, V2, and then energizes the heater group when the superconductivity is lost.

[0029] The normal use stage has two loops: The main magnet coil loop: the first main magnet coil C1-second main magnet coil C2-…-the nth main magnet coil Cn-the main coil switch S1-the first main magnet coil C1, and there is an original excitation current I10; The shielding coil loop: the first shielding coil EC1-the second shielding coil EC2-…-the nth shielding coil ECn-the shielding coil switch S2-the first shielding coil EC1, and there is an original energy storage current I20; When the main loop has a superconductivity loss point, the switch heater EH heats the shielding coil switch S2, forces the shielding coil switch S2 to be disconnected, becomes an impedance element, and thus forces I2 to flow into the first resistance heater H1-the second resistance heater H2-…-the nth resistance heater Hn loop, at this time, the first resistance heater H1, the second resistance heater H2-…-the nth resistance heater Hn generates heat to heat the corresponding main magnet coil, accelerates the superconductivity loss propagation of the main magnet, and thus makes the coil energy storage uniformly dissipate on each coil, and sequentially realizes the protection of the superconducting magnet.

[0030] Embodiment 2:

[0031] The magnet system shielding coil and superconductivity protection combined design structure provided by the preferred embodiment of the application comprises a superconducting magnet main coil and a shielding coil, a main magnet coil group and a main coil switch S1 are arranged on the main magnet coil loop, main coil loop power supply ports (V3, V4) are arranged at both ends of the main coil switch S1, the main magnet coil group is sequentially arranged as a first main magnet coil C1, a second main magnet coil C2, a third main magnet coil C3, and a fourth main magnet coil C4, and a switch heater EH is connected between the first main magnet coil C1 and the second main magnet coil C2 and between the third main magnet coil C3 and the fourth main magnet coil C4; a shielding coil group and a shielding coil switch S2 are arranged on the shielding coil loop, a heater group is arranged in parallel with the shielding coil group, the heater group is a first resistance heater H1, a second resistance heater H2, a third resistance heater H3, and a fourth resistance heater H4 that are respectively attached to and heated by the first to fourth main magnet coils, the shielding coil group is a corresponding first shielding coil EC1, a second shielding coil EC2, a third shielding coil EC3, and a fourth shielding coil EC4, shielding coil loop power supply ports (V1, V2) are arranged at both ends of the shielding coil switch S2, and the switch heater EH is close to the shielding coil switch S2 for heating the shielding coil switch S2.

[0032] The initial stage is to store energy in the shield coil group through the shield coil loop power port (V1, V2), and to energize the heater group when the superconductivity is lost.

[0033] The normal use stage is: The main magnet coil loop: the first main magnet coil C1-the second main magnet coil C2-the third main magnet coil C3-the fourth main magnet coil C4-the main coil switch S1-the first main magnet coil C1, there is an original excitation current I 10 ; The shield coil loop: the first shield coil EC1-the second shield coil EC2-the third shield coil EC3-the fourth shield coil EC4-the shield coil switch S2-the first shield coil EC1, there is an original energy storage current I 20 ; When the main loop has a superconductivity loss point, the switch heater EH heats the shield coil switch S2, forcing the shield coil switch S2 to open, becoming an impedance element, thereby forcing I2 to flow into the first resistance heater H1-the second resistance heater H2-the third resistance heater H3-the fourth resistance heater H4 loop, at this time the first resistance heater H1, the second resistance heater H2, the third resistance heater H3, and the fourth resistance heater H4 generate heat to heat the corresponding main magnet coil, accelerating the superconductivity loss propagation of the main magnet, so that the coil energy storage is evenly dissipated on each coil, and the protection of the superconducting magnet is realized in turn.

[0034] Example 3:

[0035] Based on the combined design structure of Example 1, the following magnet system shield coil and superconductivity protection combined design method is adapted: S1, simplified circuit: when the main magnet loses superconductivity, the switch heater EH generates current, heating the shield coil switch S2, forcing the shield coil switch S2 to open, becoming an impedance element, at this time I2 part (according to the total resistance of the heater group and the resistance ratio of the switch S2) flows into the first resistance heater H1-the second resistance heater H2-the third resistance heater H3-the fourth resistance heater H4, heating the remaining main magnet coil that has not lost superconductivity, accelerating the superconductivity loss, and the circuit degenerates to: LOOP1: the first inductance LEC is the equivalent inductance element of the shield coil group, the first resistance R1 is the equivalent resistance of the heater group and the shield coil switch S2 in parallel, and the second resistance R2 is the equivalent resistance of the shield coil group; LOOP2: the second inductance LC is the equivalent inductance of the main magnet coil group, the third resistance R3 is the equivalent resistance of the main magnet coil group, and the fourth resistance R4 is the equivalent resistance of the main magnet switch; S2, calculate mutual inductance; the first inductance LEC and the second inductance LC inevitable exist magnetic coupling, and the mutual inductance is set as M. In the process of losing superconductivity, the shielding coil loop will generate induced electromotive force ; Wherein, is the current in the loop LOOP2, is the incremental current generated by the inductance in the loop LOOP2; Thus resulting in the current in the loop LOOP1 ; wherein, is the incremental current generated by the inductance in the loop LOOP1, is the original energy storage current; In order to ensure that the heater is not burned in the process of losing superconductivity, the current in the loop LOOP1 The condition needs to be met Therefore, the mutual inductance M should meet the condition: ; Wherein, a is the current limiting current, the current limiting current a is I 20 The maximum current allowed after superimposing the induced current (determined by the current carrying capacity of the heater), b is a constant related to the process of losing superconductivity, R1 is the first resistance, and R2 is the second resistance; S3, optimize the mutual inductance value: the shielding coil and the superconducting protection circuit are designed jointly, firstly, in order to prevent the shielding coil from generating too high electromotive force in the process of losing superconductivity, and to burn the heater and the shielding coil switch S2, the mutual inductance between the main magnet and the shielding coil is taken as one of the objective functions of the shielding coil optimization design, secondly, under this superconducting protection circuit, The mutual inductance value needs to meet the requirement, and the shielding coil design objective function is obtained: ;

[0036] Wherein, S is the shielding factor, ppm is the magnetic field uniformity after the shielding coil and the main magnet coil are superimposed, M is the mutual inductance value, W1 / W2 / W3 is the weight factor, which is the weight of each part of the objective function f, and the weight of each part is adjusted to realize the optimization design; According to the shielding coil optimization calculation result and the constraint condition, the superconducting protection circuit is designed: .

[0037] The following is an example of actual operation. Taking a 1.5T MRI superconducting magnet as an example, the design scheme is described Table 1 is the technical parameters of superconducting magnet. According to the parameters in table 1, the shielding coil is designed and optimized, Table 1 Superconducting magnet parameters C1 C2 C3 C4 C 5 Rmin (inner radius of coil) 0.464 0.465 0.464 0.465 0.804 Rmax (outer radius of coil) 0.484 0.488 0.495 0.507 0.829 Zmin (axial Z coordinate of coil) 0.000 0.100 0.264 0.535 0.432 Zmax (axial Z coordinate of coil) 0.031 0.164 0.337 0.677 0.572 turn (number of turns per layer) 14 29 33 64 63 layer (number of layers) 12 18 20 34 16 Iop current value 520 520 520 520 -520 B0 magnetic induction 1.5 According to the technical parameters of the superconducting magnet main coil, the shield coil is placed in the gap between the main coils, as shown in Figure 4 The position constraint is added as a nonlinear constraint, and after being brought into the foregoing objective function, the initial shield coil design parameters are obtained, as shown in Table 2.

[0038] Table 2 Initial shield coil design parameters Rmin (inner radius of coil) Rmax (outer radius of coil) Zmin (axial Z coordinate of coil) Zmax (axial Z coordinate of coil) Layer (number of layers) Turn (number of turns per layer) current direction (current direction) A+ 0.5005895 0.502011 0.187619341 0.2097993410 1 10 1 B+ 0.5175895 0.519011 0.377976196 0.3935021964 1 7 1 C+ 0.8299 0.8313 0.4328 0.5725 1 32 1 A- 0.5005895 0.502011 -0.2097993410 -0.187619341 1 10 1 B- 0.5175895 0.519011 -0.3935021964 -0.377976196 1 7 1 C- 0.8299 0.8313 -0.5725 -0.4328 1 32 1 The mutual inductance value M between the shield coil and the main coil is 0.0398 H.

[0039] According to the relationship between the mutual inductance and the resistance value of the protection circuit , it is calculated that the parallel resistance value R2 of the heater group and the shield coil switch S2 should be R2≥8Ω, the resistance Re of the shield coil switch S2 is 10Ω, and the total resistance of the heater group is Rh≥40Ω.

[0040] According to the above results, the quench protection circuit parameters are designed: the first resistance heater H1=the second resistance heater H2=the third resistance heater H3=the fourth resistance heater H4=25Ω; and the shield coil switch S2=10Ω.

[0041] The above only describes the preferred embodiments of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement and improvement made by any person skilled in the art within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A combined design structure for a magnet system shielding coil and quench protection, characterized in that: It includes a superconducting magnet main coil and a shielding coil. The main magnet coil circuit is equipped with a main magnet coil group and a main coil switch (S1). Power-on ports (V3, V4) are located at both ends of the main coil switch (S1). The main magnet coil group consists of a first main magnet coil (C1), a second main magnet coil (C2), ..., an nth main magnet coil (Cn) arranged sequentially. A switch heater (EH) is connected at both ends to the first main magnet coil (C1) and the nth main magnet coil (Cn), with one or more main magnet coils serving as a heating current source. A shielding coil group is also provided on the shielding coil circuit. A shielded coil switch (S2) is provided with a heater group connected in parallel with the shielded coil group. The heater group consists of a first resistance heater (H1), a second resistance heater (H2), ..., an nth resistance heater (Hn) that are respectively attached to and heated with the first to nth main magnet coils. The shielded coil group consists of the corresponding first shielded coil (EC1), second shielded coil (EC2), ..., an nth shielded coil (ECn). A shielded coil circuit power supply port (V1, V2) is provided at both ends of the shielded coil switch (S2). The switch heater (EH) is close to the shielded coil switch (S2) to heat the shielded coil switch (S2).

2. The combined design structure of a magnet system shielding coil and quench protection according to claim 1, characterized in that: n is a natural number greater than or equal to 1.

3. The combined design structure of a magnet system shielding coil and quench protection according to claim 2, characterized in that: n is a natural number between 4 and 9.

4. The combined design structure of a magnet system shielding coil and quench protection according to claim 1, characterized in that: In the initial stage, energy is stored in the shielded coil group through the power supply ports (V1, V2) of the shielded coil circuit, and then used to power the heater group after the timeout.

5. The combined design structure of a magnet system shielding coil and quench protection according to claim 1, characterized in that: During normal use, the two circuits are: Main magnet coil circuit: First main magnet coil (C1) - Second main magnet coil (C2) ... nth main magnet coil (Cn) - Main coil switch (S1) - First main magnet coil (C1), with initial excitation current I. 10 ; Shielded coil circuit: First shielded coil (EC1) - Second shielded coil (EC2) ... nth shielded coil (ECn) - Shielded coil switch (S2) - First shielded coil (EC1), with initial energy storage current I. 20 ; When a quench point exists in the main circuit, the switch heater (EH) heats the shielded coil switch (S2), forcing the shielded coil switch (S2) to open and become an impedance element. This forces a portion of I2 to flow into the circuit of the first resistance heater (H1) - the second resistance heater (H2) ... the nth resistance heater (Hn). At this time, the first resistance heater (H1), the second resistance heater (H2) ... the nth resistance heater (Hn) generate heat to heat the corresponding main magnet coil, accelerating the quench propagation of the main magnet. This allows the energy stored in the coil to be evenly dissipated on each coil, thus protecting the superconducting magnet in sequence.

6. The combined design structure of a magnet system shielding coil and quench protection according to claim 1, characterized in that: The number of main magnet coils connected to both ends of the switch heater (EH) is matched to its heating requirements.

7. A method for jointly designing a shielding coil and quench protection for a magnet system, characterized in that: Based on the joint design structure of any one of claims 1-6, the following steps are adapted: S1, Simplified Circuit: When the main magnet loses quench, the circuit degenerates into: LOOP1: The first inductor (LEC) is the equivalent inductance element of the shielded coil group, the first resistor (R1) is the equivalent resistance of the heater group and the shielded coil switch (S2) in parallel, and the second resistor (R2) is the equivalent resistance of the shielded coil group; LOOP2: The second inductor (LC) is the equivalent inductance of the main magnet coil group; S2, calculate the mutual inductance value; the first inductor (LEC) and the second inductor (LC) inevitably have magnetic coupling, and their mutual inductance value is set as M. During the loss of quench, the shielding coil circuit will generate an induced electromotive force. ； in, The current in loop LOOP2, 'This is the incremental current generated by the inductor in loop LOOP2; This results in current flowing through loop LOOP1. ； in, It is the incremental current generated by the inductor in loop LOOP1. This is the original energy storage current; To ensure the heater does not burn out during the quench process, the current in loop LOOP1 is... To satisfy the condition, the mutual inductance M should satisfy the following condition: ； Where a is the current limiting current, b is a constant related to the quench process, R1 is the first resistor, and R2 is the second resistor; S3, Optimize mutual inductance: The shielding coil and quench protection circuit are designed together. First, to prevent the shielding coil from generating excessively high electromotive force during the quench process, which could burn out the heater and the shielding coil switch (S2), the mutual inductance between the main magnet and the shielding coil is used as one of the objective functions for the optimized design of the shielding coil. Second, under this quench protection circuit, To meet the mutual inductance requirements, the objective function for shielded coil design is obtained: ； Where S is the shielding factor, ppm is the magnetic field uniformity after the shielding coil and the main magnet coil are superimposed, M is the mutual inductance value, and W1 / W2 / W3 are weighting factors. Design a quench protection circuit based on the optimized calculation results and constraints of the shielding coil: 。 8. The method for jointly designing a shielding coil and quench protection for a magnet system according to claim 7, characterized in that: In step S1, when the main magnet loses quench, a current is generated in the switch heater (EH), which heats the shielded coil switch (S2), forcing the shielded coil switch (S2) to open and become an impedance element. At this time, a portion of I2 flows into the first resistance heater (H1), the second resistance heater (H2), the third resistance heater (H3), and the fourth resistance heater (H4), heating the remaining main magnet coils that have not lost quench, thus accelerating the loss of quench.

Images