JP6310221B2 - Passive quench detection method for superconducting magnets - Google Patents

Description

  The present invention relates to a technical field of a passive quench detection method for a superconducting magnet in which a plurality of superconducting coils are connected in series via connection points.

  In a device using electromagnetic characteristics such as an electric device such as an electric motor or a generator or a medical diagnostic apparatus such as MRI, a strong magnetic field is often required. Generally, a strong magnetic field can be obtained by a permanent magnet such as samarium / cobalt or neodymium / iron / boron, but the maximum magnetic flux density B that can be used by a single permanent magnet is limited to about 0.5T. Yes. As a means for obtaining a stronger magnetic field, for example, a Halbach magnetic circuit combining a permanent magnet is known. The Halbach magnetic circuit forms a doughnut-shaped magnetic circuit by arranging permanent magnets in accordance with the distribution direction of the dipole magnetic field created by the permanent magnets, thereby generating a uniform strong magnetic field in the central portion. FIG. 12 shows a configuration example of the Halbach magnetic circuit 40, which is configured by combining a plurality of permanent magnets 42 in a hollow casing 41, and realizes a maximum magnetic flux density B = 1.5 (T).

  The Halbach magnetic circuit is configured by combining a plurality of magnetized permanent magnets, and requires an enormous amount of force to assemble it. Thus, it is difficult to obtain a stronger magnetic field. Thus, superconducting magnets have recently attracted attention as means for obtaining a stronger magnetic field. A superconducting magnet is formed by winding a superconducting wire having an electric resistance value of zero at a direct current in a cryogenic state in a coil shape, and can easily generate a strong magnetic field of several T or more by flowing a large current. it can.

  When a superconducting magnet is used, a superconducting phase is suddenly broken and then transferred to the normal conducting phase, so that a superconducting coil is destroyed (burned out). Avoiding this is important for the practical application of superconducting magnets. Various causes of the quenching phenomenon are considered, and one of the causes is a wire movement in which a part of the superconducting coil winding moves locally. For example, if a part of the superconducting coil winding moves while being minute for some reason, an electromotive force is generated by movement of the wire in the magnetic field, and heat is generated. When the temperature rises above the critical temperature of the superconducting wire due to heat generation, the superconducting phase breaks down and is observed as a quench phenomenon. Such a quenching phenomenon causes a serious failure such as fusing of the superconducting coil winding, so that it is required to detect it early and accurately.

  Various techniques have been studied for this type of quench detection method, and examples thereof include Patent Documents 1 and 2. In Patent Document 1, a superconducting coil is divided into a plurality of sections using voltage taps, and quench detection is performed by measuring each potential difference. In Patent Document 2, a bridge circuit is configured using an intermediate tap provided in a superconducting coil, and quench detection is performed based on a voltage detection value in the bridge circuit.

JP 2012-248725 A JP 54-96391 A

  If the cooling temperature of the superconducting coil is sufficiently secured, even if local heat is generated in the coil, the temperature rise is small while the specific heat of the magnet material is sufficiently large, and the quench phenomenon is difficult to occur. In general, superconductors can be broadly divided into metal superconductors used at helium temperature and high-temperature superconductors such as Y-based or Bi-based having a higher critical temperature than the metal superconductor. The high temperature superconductor can be operated in a temperature range where the specific heat is larger than that of the metal superconductor, and therefore it is said that the quench phenomenon is unlikely to occur. However, depending on the use of the superconducting magnet, the superconducting wire is exposed to a strong magnetic field, the critical temperature is lowered, and the risk of occurrence of the quench phenomenon may be increased.

  When a superconducting wire used in a superconducting magnet is formed of a high-temperature superconductor, a tape-shaped wire is generally used because of restrictions on the manufacturing method of the superconducting wire. When a superconducting wire having such a tape wire shape is used as a coil winding, the pancake structure shown in FIG. 13 is widely adopted. In this example, the first superconducting coil L1 wound in a pancake shape from the outside to the inside and the second superconducting coil L2 wound in a pancake shape from the inside to the outside are arranged on the inside. 2 has a so-called double pancake structure electrically connected continuously. Such a double pancake structure has an advantage that a strong magnetic field can be easily generated by increasing the number of layers while being connected at the outer peripheral portion having a low magnetic field strength.

  On the other hand, a superconducting wire in the form of a tape wire has a smaller heat transfer characteristic than a general wire having a substantially circular cross section due to its thinness. For this reason, when a normal conducting phase occurs, it is likely to cause a serious failure such as fusing due to heat generation, so that it is required to detect the quench phenomenon at an earlier stage.

  In Patent Document 1, quench detection is performed based on a voltage measurement value in a predetermined section of a superconducting coil. However, such voltage measurement values include a lot of noise due to the DC power source of the superconducting coil, and it is difficult to detect quench with high accuracy. On the other hand, in Patent Document 2, since quench detection is performed using a bridge circuit, it is considered that the detection accuracy is relatively improved as compared with Patent Document 1 described above. However, with the detection technique of Patent Document 2, quench detection of a superconducting coil having a simple configuration is possible. However, when an attempt is made to apply to a superconducting magnet composed of a large number of superconducting coils, a similar detecting device is used for the number of coils. Therefore, there is a problem that the configuration becomes complicated.

  Further, when a plurality of superconducting coils are electrically connected, each superconducting coil is affected by mutual inductance. Therefore, the behavior of the both-ends voltage of each superconducting coil when quenching occurs is complicated unlike the simple system as described above. Therefore, there is a problem that accurate quench detection is difficult only by applying the above technique as it is.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a passive quench detection method for a superconducting magnet capable of accurately detecting a quench phenomenon with a simple configuration in a superconducting magnet including a plurality of superconducting coils. And

  In order to solve the above-mentioned problem, a passive quench detection method for a superconducting magnet according to the present invention is configured such that N (where N is an integer of 2 or more) superconducting coils are connected in series via a connection point. A superconducting magnet quench detection method comprising: (i) N reference resistors connected in series with each other and connected in parallel to the N superconducting coils; and (ii) of the N superconducting coils. (N-1) first leads connected to a connection point between adjacent superconducting coils, and (iii) connected to a connection point between adjacent reference resistors among the N reference resistors (N -1) a circuit configuration step of forming a bridge circuit by incorporating the second leads into the N superconducting coils, the first lead, and the second lead A combination of a voltage detection step for detecting the voltage of the voltage and a detected value of the voltage in the voltage detection step when quenching is detected in any of the N superconducting coils is prepared in advance, A quench detection step for identifying in which of the N superconducting coils quench is detected by comparing the actual value detected in the voltage detection step with the combination of the detection values prepared in advance. It is characterized by providing.

  According to the present invention, in a superconducting magnet composed of N superconducting coils, quench detection can be accurately performed by measuring the voltage of the bridge circuit constructed in each superconducting coil. In particular, the accuracy of considering the influence of mutual inductance between each superconducting coil by preparing a combination of voltage detection values when quenching is detected in one of the superconducting coils and comparing it with the actual voltage detection value. It is possible to make a good quench detection determination. As a result, it is possible to specify which of the superconducting coils the quench is detected in, and it is possible to obtain useful information when analyzing the location of occurrence of quenching at a later date. it can.

In one aspect of the present invention, the N reference resistors are adjusted so that the detected voltage value in the voltage detection step is substantially zero in a normal state where no quenching occurs in the N superconducting coils. A process may be provided.
According to this aspect, in the normal state where the quench phenomenon does not occur, the detected value between the first lead and the second lead is balanced so that the detected value is substantially zero. When the electrical resistance value in the superconducting magnet increases due to the occurrence, the balance is lost, and a voltage detection value that is not substantially zero is detected.

In another aspect, the N reference resistors may be variable resistors using constantan as a resistance material.
Constantan has excellent stability in both temperature and magnetic field characteristics, making it suitable as a reference resistance material for quench detection based on minute voltage changes in the harsh environment of superconducting magnets at extremely low temperatures and strong magnetic fields. Yes.

Each of the N superconducting coils may have a double pancake structure.
In the double pancake structure, since the superconducting coils are connected to each other through a connection point, a reference resistor, a first lead, and a second lead are incorporated into the connection point to easily configure the bridge circuit. be able to.

  According to the present invention, in a superconducting magnet composed of N superconducting coils, quench detection can be accurately performed by measuring the voltage of the bridge circuit constructed in each superconducting coil. In particular, the accuracy of considering the influence of mutual inductance between each superconducting coil by preparing a combination of voltage detection values when quenching is detected in one of the superconducting coils and comparing it with the actual voltage detection value. It is possible to make a good quench detection determination. As a result, it is possible to specify which of the superconducting coils the quench is detected in, and it is possible to obtain useful information when analyzing the location of occurrence of quenching at a later date. it can.

It is the schematic which shows the whole structure of the quench detection apparatus which concerns on a reference example. It is a graph which shows the time change of the magnet current in a reference example, and the both-ends voltage of a superconducting coil. It is the schematic which shows the whole structure of the quench detection apparatus which concerns on 1st Example. It is an equivalent circuit of the quench detection apparatus shown in FIG. It is a graph which shows the time change of the detected value of the voltage detection part in 1st Example with the magnet current and the both-ends voltage of a superconducting coil. It is a schematic diagram which shows the whole structure of the quench detection apparatus which concerns on 2nd Example. It is a graph which shows the example of a measurement of the detected value of the voltage detection part in the 2nd example. It is the graph which expanded and showed Drawing 7 (a). The detection value Vm1 (t) is representatively extracted from FIG. 8 and enlarged. It is a schematic diagram which shows the structural example of a reference resistance. It is a graph which shows the temperature characteristic of an electrical resistivity about a some metal material. It is a schematic diagram which shows the structural example of a Halbach magnetic circuit. It is a schematic diagram which shows the structural example of the superconducting magnet which has a pancake structure.

  Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. This is just an example.

(Reference example)
First, with reference to FIG. 1, a reference example that is a premise for the present invention will be described. Here, a case where a superconducting magnet that is a detection target of quenching is composed of superconducting coils having equal inductances L1 and L2 to have a simple structure will be described. FIG. 1 is a schematic diagram showing the overall configuration of a quench detection device 10 ′ according to a reference example.

The superconducting magnet to be detected by quenching is composed of two superconducting coils L1 and L2 having a double pancake structure connected in series with each other (that is, N = 2). The superconducting coils L1 and L2 have an electric circuit 4 in which a DC power source 3 operating with a commercial power source is connected in series. In FIG. 1, the DC current (magnet current) flowing through the electric circuit 4 is indicated by Idc. Yes. In the electric circuit, an ammeter 6 for measuring the magnet current Idc is provided in series, and a voltmeter 7 for measuring the voltage Vdc across the superconducting coils L1 and L2 is provided in parallel. The detection values of the ammeter 6 and the voltmeter 7 are sent to a detection unit 5 (for example, an electronic computer or various measuring instruments) for performing calculation analysis of the detection values, and quench detection is performed.
The resistor RX inserted in series in the electric circuit 4 has various resistance components included in the electric circuit 4 such as the internal resistance of the DC power source 3 and various connection resistances and current leads in the superconducting coils L1 and L2. It is expressed collectively.

  The magnitude of the direct current Idc flowing through the electric circuit 4 is controlled by a power supply controller (not shown) according to the magnitude of the magnetic field to be generated in the superconducting coils L1 and L2. Here, the current value Idc is a constant time constant determined by the inductance component L and the resistance component R included in the electric circuit 4, and the current change is gradually increased to gradually increase the power supply voltage, so that the superconducting coil current becomes a predetermined value. Controlled to increase up to.

  A verification example of quench detection using a reference example is shown in FIG. Note that the superconducting coils L1 and L2 constituting the superconducting magnet used for this verification have self-inductance L1 = L2 = 0.1 (H), mutual inductance M = 0.099 (H), and all resistances including current leads, respectively. The one of 30 (mΩ) was used. In addition, the DC power source 3 adopting a switching method was used, and the output voltage was driven at a constant voltage of 2 (V) (however, it included white noise of ± 200 mV). Usually, the power supply voltage is gradually increased while observing the state of the superconducting magnet. Here, assuming a practical device, the power supply voltage is assumed to be constant at 2 (V) from the initial state.

  In FIG. 2, the magnet current Idc flowing through the electric circuit 4 and the voltage Vdc across the superconducting magnet are shown. In this example, the magnet current Idc is controlled to gradually increase by the power supply controller, and when the time t1 is reached, the quench phenomenon starts to appear due to the occurrence of the normal conducting phase at L2 of the two superconducting coils. The measurement results are shown. However, as shown in FIG. 2, in the reference example, since no remarkable change is observed in the behavior of the magnet current Idc and the terminal voltage Vdc, it is difficult to detect the quench at this point.

  When the increase of the magnet current Idc by the power supply controller is further continued, the magnet current Idc flowing through the electric circuit 4 starts to decrease at time t2. In the reference example, at time t2, the occurrence of the quench phenomenon is grasped by detecting the abnormal phenomenon that the magnet current Idc decreases despite the current increase control by the power supply controller. Therefore, in the reference example, in order to detect the quench phenomenon, it is necessary to wait until time t2, and detection at the time t1 is not possible. At time t2, the magnet current Idc has reached a large value, which may lead to a serious failure such as burning of the superconducting coils L1 and L2. Actually, when the normal conducting layer is generated, cold liquid helium and nitrogen boils violently, so it can be detected that an abnormality has occurred from the physical phenomenon, but it is difficult to detect the quench phenomenon electrically. It is.

There are many reports that the quench phenomenon is likely to occur in the process of increasing the magnet current Idc. When the magnet current Idc is increased, a large counter electromotive force is generated by the superconducting coils L1 and L2, and thus there is a problem that it is difficult to discriminate and detect a minute increase in electric resistance value caused by the quench phenomenon.
In addition, when detecting a minute voltage due to the quench phenomenon, if noise enters the various wirings that transmit and receive the voltage signal, the minute electric signal due to the quench phenomenon will be buried in the large noise, causing the quench phenomenon to occur. There is also a problem that it is difficult to distinguish. Also in the verification example of FIG. 2, since the switching type DC power supply 3 is used, large white noise is mixed in the both-end voltage Vdc, and it is shown that quench detection by a minute voltage change becomes difficult.
Such a problem can be solved by a detection method using a bridge circuit described below (hereinafter referred to as “basic technique” as appropriate).

(Basic technology)
FIG. 3 is a schematic diagram showing the overall configuration of the quench detection device 10 using a bridge circuit, and FIG. 4 is an equivalent circuit of the quench detection device 10 shown in FIG. In addition, suppose that the same code | symbol is attached | subjected to the same part as the said reference example, and the overlapping description is abbreviate | omitted suitably.

  In the basic technology, in order to explain the principle of the present invention described later in an easy-to-understand manner, the case where the superconducting magnet is composed of two equivalent superconducting coils L1 and L2 will be described as an example. This basic technique is applicable when the superconducting magnet is composed of an even number of superconducting coils, and these even number of superconducting coils can be divided into two equal groups. If the superconducting magnet is composed of an odd number of superconducting coils or if the superconducting magnet is composed of an even number of superconducting coils but cannot be divided into two equal groups, a book to be described later will be described. By applying the invention, quench can be detected with high accuracy.

  In the quench detection device 10, the reference resistors R1 and R2 connected in series with each other are connected in parallel to the superconducting coils L1 and L2, and the first lead connected to the midpoint 12 of the reference resistors R1 and R2. 13 and a bridge circuit 15 configured to have a second lead 14 connected to the midpoint 11 of the superconducting coils L1 and L2. A voltage detector 16 is provided between the first lead 13 and the second lead 14. The detection value Vm (t) of the voltage detection unit 16 is sent to the detection unit 5 that analyzes the detection signal, and the quench phenomenon can be detected based on the detection value.

  The reference resistors R1 and R2 are preferably arranged in the vicinity of the superconducting coils L1 and L2 so that the influence of the electric resistance of the first lead 13 and the second lead 14 is reduced. For this reason, it is desirable to employ reference resistors R1 and R2 that are less affected by the magnetic field and temperature.

ここで、ｅ０は直流電源３の出力電圧値であり、ｅ２、ｅ３、ｅ４はそれぞれ図４に示すブリッジ回路１５上の各ポイントにおける電圧値を示しており、ｉ１（ｔ）及びｉ２（ｔ）は、それぞれ図４に示すブリッジ回路１５上の各ポイントにおける電流値を示している。
またブリッジ回路１５には、例えば抵抗成分として直流電源３の内部抵抗ＲＩＮ、電流リード１３及び１４のそれぞれの抵抗ＲＬ１、ＲＬ２、更に各超電導コイルＬ１及びＬ２内における種々の接続抵抗ＲＩＮｃ１、ＲＩＮｃ２が存在する。図３及び図４では、これらの抵抗成分を全抵抗値ＲＸとして示している。尚、厳密には

であるが、以下の説明では

と近似して簡略化する。
尚、Ｍは超電導コイルＬ１及びＬ２の相互インダクタンスであり、磁気結合係数Ｋを用いると、

の関係が成立する。 Here, when a circuit equation is obtained for the equivalent circuit of FIG. 4, the following equation is obtained.

Here, e0 is the output voltage value of the DC power source 3, and e2, e3, e4 are the voltage values at each point on the bridge circuit 15 shown in FIG. 4, and i1 (t) and i2 (t) Indicates current values at respective points on the bridge circuit 15 shown in FIG.
In addition, the bridge circuit 15 includes, for example, an internal resistance RIN of the DC power source 3, resistances RL 1 and RL 2 of the current leads 13 and 14 as resistance components, and various connection resistances RINc 1 and RINc 2 in the superconducting coils L 1 and L 2. To do. 3 and 4, these resistance components are shown as the total resistance value RX. Strictly speaking,

However, in the following explanation

Approximate and simplify.
M is the mutual inductance of the superconducting coils L1 and L2, and when the magnetic coupling coefficient K is used,

The relationship is established.

  Here, it is assumed that the inductances L1 and L2 of the superconducting coil and the reference resistors R1 and R2 in the bridge circuit 15 are equal to each other. In a normal state in which no quench phenomenon occurs in the superconducting coils L1 and L2, the bridge circuit 15 is symmetric with respect to the voltage detection unit 16, and thus the detection value Vm (t) of the voltage detection unit 16 is substantially zero. On the other hand, when the quench phenomenon occurs in at least one of the superconducting coils L1 and L2, the balance in the bridge circuit 15 is lost, and the absolute value of the detection value Vm (t) of the voltage detection unit 16 indicates a value other than substantially zero. .

  FIG. 5 shows a verification example using the quench detection device 10 according to the first embodiment. In this verification example, the self-inductance of the superconducting coil is L1 = L2 = 0.1 (H), the mutual inductance is M = 0.99 (H), the reference resistance is R1 = R2 = 10 (Ω), and the total resistance is RX = 0.1 (Ω), and the output voltage of the DC power supply 3 was set to be kept constant at e0 = 2 (V). The magnet current Idc was gradually increased by controlling the DC power supply 3 with a power supply controller.

At time t1, which is the start timing of the quench phenomenon, no abnormality is observed in the behavior of the magnet current Idc and the terminal voltage Vdc itself, as in the reference example shown in FIG. However, the detected voltage Vm (t) of the voltage detector 16 shows a clear increasing tendency after time t1. This means that the electrical resistance value of the superconducting coils L1 and L2 increases due to the quench phenomenon, and the balance in the bridge circuit 15 is lost.
The detection unit 5 stores a threshold value Vref in a storage unit such as a memory in advance, and determines that a quench phenomenon has occurred when the absolute value of the detection value Vm (t) of the voltage detection unit 16 exceeds the threshold value Vref. To detect.
As described above, the quench detection device 10 can detect the voltage change caused by the minute change in the electric resistance value generated in the superconducting magnet using the bridge circuit 15.

  FIG. 5 shows a case where quenching occurs in L2 of the two superconducting coils constituting the superconducting magnet, and correspondingly, the detected voltage Vm (t) is generated so that the sign is positive. . On the other hand, when quenching occurs in L1 of the two superconducting coils constituting the superconducting magnet, the detection voltage Vm (t) is generated so that the sign is negative. Thereby, in the basic technology, in addition to detecting the presence or absence of quenching by comparing the absolute value of the detection voltage Vm (t) with the threshold value Vref, it is specified which superconducting coil has caused the quenching. Can do.

  Further, the terminal voltage Vdc shown in FIG. 5 mainly includes white noise caused by the DC power supply 3. As described above with reference to FIG. 2, a large white noise appears in the both-end voltage Vdc, but the detection voltage Vm in the bridge circuit 15 is hardly affected by such noise. This is because the noise from the DC power supply 3 enters the superconducting coils L1 and L2 and the reference resistors R1 and R2 arranged in contrast with each other in the same phase. This is because these noises are canceled out in the detection signal Vm (t). Thus, the quench detection device 10 according to the present embodiment can reduce the influence of noise and perform accurate quench detection.

  Although the above embodiment has been described with respect to the case where the DC power source 3 is driven at a constant voltage, even when the DC power source 3 is driven at a constant current, the current to the reference resistors R1 and R2 is supplied from a separate power source based on the same principle. Quench detection can be performed.

  Such a quench detection device 10 can be applied when the superconducting coils constituting the superconducting magnet are an even number and the plurality of superconducting coils can be divided into two groups, but the superconducting magnet is an odd number. There is a problem that it cannot be applied to a case where it is not possible to divide into two equivalent groups even if it is composed of a single superconducting coil or a superconducting magnet is composed of an even number of superconducting coils.

  Further, in the above-described quench detection device 10, it is necessary to determine based on the sign of the detection voltage Vm (t) between two equivalent groups when specifying the quench occurrence location. There is a problem that it cannot be applied when it is composed of two or more superconducting coils.

Further, in the above-described quench detection device 10, it is necessary to perform initial setting so that the detection voltage Vm (t) becomes zero in a state where no quench occurs. Such initial setting is relatively easy when the number of superconducting coils constituting the superconducting magnet is small, but as the number of superconducting coils increases, the interaction between the superconducting coils increases. The effect of the variation of individual differences becomes larger, and the difficulty of initial setting becomes higher. Therefore, there is a problem that accurate quench detection becomes difficult.
These problems can be solved by the embodiments of the present invention described below.

(Example)
In the present embodiment, a case where the present invention is applied to a superconducting magnet composed of more superconducting coils will be described as an example (that is, N> 3).

となる。 FIG. 6 is a schematic diagram illustrating the overall configuration of the quench detection device 20 according to the present embodiment. The superconducting magnet to be detected is configured by connecting superconducting coils L1 to L5 having a double pancake structure in series with each other (when N = 5). Reference resistors R1 to R5 connected in series with each other are connected in parallel to the superconducting coils L1 to L5, and between the midpoint 21a between the superconducting coils L1 and L2 and the midpoint 22a between the reference resistors R1 and R2. Is provided with a voltage detection unit 23a, and a voltage detection unit 23b is provided between a midpoint 21b between the superconducting coils L2 and L3 and a midpoint 22b between the reference resistors R2 and R3. A voltage detector 23c is provided between the point 21c and the midpoint 22c between the reference resistors R3 and R4, and between the midpoint 21d between the superconducting coils L4 and L5 and the midpoint 22d between the reference resistors R4 and R5. The bridge circuit 24 is configured by providing the voltage detection unit 23d.
Here, when the connection point potentials at the middle points 21a to 21d are defined as e2 (t) to e5 (t) and the connection point potentials at the middle points 22a to 22d are defined as e6 (t) to e9 (t), the voltage detection means 23a to The detection voltage at 23d is

It becomes.

と表される。理想的なコイルでは磁束鎖交割合が１００％であるためＫｉｊ＝１であるが、実際には少なからず各コイルの隙間から磁力線が漏洩する。このような事実を反映させるために、隣り合う超電導コイル同士の磁気結合係数を９９％、一つ置き超電導コイル同士の磁気結合係数を９８％、二つ置き超電導コイル同士の磁気結合係数を９７％であると仮定する。 Although it is ideal to use the same superconducting magnets L1 to L5, this embodiment can also be applied to a case where the superconducting magnet is composed of superconducting coils having different inductances. Because there is a limit, there will be some individual differences). Therefore, in this embodiment, the self-inductance L1 = 10 (mH), L2 = 10.2 (mH), L3 = 10.1 (mH), L4 = 9.9 ( mH), L5 = 9.9 (mH). In the superconducting magnet, the mutual inductance is also important because each superconducting coil is magnetically coupled. Therefore, using the magnetic coupling coefficient Kij of the superconducting coils Li and Lj (i and j are arbitrary integers), the mutual inductance is

It is expressed. In an ideal coil, the magnetic flux linkage ratio is 100%, so Kij = 1. However, the magnetic field lines actually leak from the gaps between the coils. In order to reflect this fact, the magnetic coupling coefficient between adjacent superconducting coils is 99%, the magnetic coupling coefficient between every two superconducting coils is 98%, and the magnetic coupling coefficient between every two superconducting coils is 97%. Assume that

尚、リファレンス抵抗はＲ１＝Ｒ２＝Ｒ３＝Ｒ４＝Ｒ５＝１０（Ω）と仮定する。 Based on such an assumption, in the case of a superconducting magnet composed of superconducting coils L1 to L5, the magnetic coupling coefficient in each superconducting coil is expressed by the following equation.

The reference resistance is assumed to be R1 = R2 = R3 = R4 = R5 = 10 (Ω).

  FIG. 7 is a graph illustrating a measurement example of the detection values Vm1 (t) to Vm4 (t) of the voltage detection units 23a to 23d. FIG. 7A shows the case where a quench phenomenon occurs in the superconducting coil L1, FIG. 7B shows the case where a quench phenomenon occurs in the superconducting coil L2, and FIG. 7C shows the superconducting coil. FIG. 7 (d) shows a case where a quench phenomenon occurs in the superconducting coil L4, and FIG. 7 (e) shows a case where a quench phenomenon occurs in the superconducting coil L5. Is shown.

  According to FIG. 7A, when the superconducting coil L1 is quenched, all of the detection values Vm1 (t) to Vm4 (t) of the voltage detection units 23a to 23d show a decreasing tendency after the time t1. According to FIG. 7B, when the superconducting coil L2 is quenched, after time t1, only the detection value Vm1 (t) of the voltage detection unit 23a tends to increase, while the remaining detection values Vm2 (t) to Vm4. (T) shows a decreasing trend. According to FIG. 7 (c), when the superconducting coil L3 is quenched, the detected values Vm1 (t) and Vm2 (t) of the voltage detectors 23a and 23b show an increasing tendency after the time t1, while the remaining detected values Vm3 (t) and Vm4 (t) show a decreasing tendency. According to FIG. 7D, when the superconducting coil L4 is quenched, the detected values Vm1 (t) to Vm3 (t) of the voltage detectors 23a to 23c show an increasing tendency after the time t1, while the remaining detected values. Only Vm4 (t) shows a decreasing trend. According to FIG. 7 (e), when the superconducting coil L5 is quenched, all of the detected values Vm1 (t) to Vm4 (t) of the voltage detectors 23a to 23d show an increasing tendency after the time t1.

  When a bridge circuit is configured for a plurality of superconducting coils as described above, the increase / decrease patterns of the detected values Vm1 (t) to Vm3 (t) are different depending on which superconducting coil is quenched. Such increase / decrease patterns of the detection values Vm1 (t) to Vm3 (t) are specified according to the number of superconducting coils constituting the superconducting magnet and the connection state. In the present embodiment, as will be described below, quenching can be accurately performed even in a superconducting magnet composed of a large number of superconducting coils by analyzing the increase / decrease pattern of each detected value Vm1 (t) to Vm3 (t). While detecting, the generation | occurrence | production location can be specified.

First, similarly to the basic technique, the detection unit 5 stores a threshold value Vref serving as a detection criterion for the quench phenomenon in a storage unit such as a memory in advance, and absolute values of the detection values Vm1 (t) to Vm4 (t). When the value exceeds the threshold value Vref, the occurrence of the quench phenomenon can be specified. In this embodiment, since the superconducting coils L1 to L4 have substantially the same inductance, a common threshold value Vref is set. However, a threshold value may be individually set for each of the superconducting coils L1 to L4.
The detection unit 5 monitors the occurrence of quench in each of the superconducting coils L1 to L4, and when the quench is detected in any of the superconducting coils L1 to L4, an alarm may be issued to notify the operator.
Thereby, even in a superconducting magnet composed of a large number of superconducting coils, accurate quench detection using a bridge circuit can be performed.

  In addition, the detection unit 5 can specify in which superconducting coil the quench has occurred based on the change patterns of the detected values Vm1 (t) to Vm4 (t) of the superconducting coils L1 to L4. Specifically, storage means such as a memory is built in the detection unit 5, and each of the detection values Vm1 (t) to Vm4 (t) when quenching occurs in each of the superconducting coils L1 to L4 in the storage means. The behavior is prepared in advance as data. Then, by comparing the actually detected values Vm1 (t) to Vm4 (t) with the stored data, it is possible to specify in which part of the superconducting coil constituting the superconducting magnet the quench has occurred.

  Note that the data stored in the storage means may include at least the signs of the detected values Vm1 (t) to Vm4 (t) when quenching occurs in each of the superconducting coils L1 to L4. Thereby, even when a bridge circuit is provided in a superconducting magnet composed of a large number of superconducting coils, the occurrence location of the quench and the detected values Vm1 (t) to Vm4 (t) while taking into account the interaction between the superconducting coils L1 to L4. ) Can be correlated to perform accurate quench detection.

  FIG. 8 is an enlarged view of FIG. 7A, and FIG. 9 is a representative extraction of the detected value Vm1 (t) from FIG. As described above in the basic technique, the detection values Vm1 (t) to Vm4 (t) in the bridge circuit 24 are not easily affected by noise, but as shown in FIGS. 8 and 9, noise is completely removed. It is difficult to do so, and noise having a maximum amplitude of about 0.1 (mV) appears in the detected value. In addition, an offset voltage of 2.6 (mV) at maximum appears, which makes it difficult to accurately detect the quench start point. This is because the reference resistors R are all set to be equal to 10Ω even though the inductances L1 to L5 of the respective superconducting coils are not completely the same value. That is, since the actual superconducting coil has a considerable manufacturing variation, the bias voltage resulting from the interaction between the superconducting coils is added to the detection values Vm1 (t) to Vm4 (t) as noise.

  In order to further suppress the influence of such noise, it is effective to perform so-called calibration that optimizes the reference resistors R1 to R5 in accordance with variations in the inductances L1 to L5 of each superconducting coil. In this example, the reference resistors are R1 = 10.01 (Ω), R2 = 10.23 (Ω), R3 = 10.18 (Ω), R4 = 10.06 (Ω), R5 = 10.00, respectively. When adjusted to (Ω), the effect of noise was minimized.

Such optimization of the reference resistors R1 to R5 can be easily realized by adopting, for example, a resistor having the configuration of FIG. FIG. 10 is a schematic diagram illustrating a configuration example of the reference resistors R1 to R5.
The reference resistor R1 shown in FIG. 10 is configured as a variable resistor by providing a sliding portion 32 on a non-inductive winding resistor formed by non-inductively winding a resistance wire 31 on an FRP rod 30 having a diameter of 5 (mmφ). The sliding part 32 connected to the bolt screw 33 can be moved up and down by rotating the bolt screw 33 provided on the upper part. By moving the position of the sliding portion 32 in this manner, the length of the resistance wire 31 wound around the non-inductive winding resistance can be adjusted, and a subtle change in the electric resistance value can be achieved. Yes.

Here, the material used for the resistance wires of the reference resistors R1 to R5 is preferably a metal material having little temperature dependency and magnetic field dependency (for example, an inexpensive carbon resistor as a resistor used in a general telecommunication circuit) However, it is not preferable because the temperature change is large.)
FIG. 11 is a graph showing temperature characteristics of electrical resistivity for a plurality of metal materials having relatively high resistivity. In this example, Invar, Nichrome, Constantan, and Brass are representatively shown, but the constant resistivity of Constantan is shown to be most stable with respect to the temperature change (by the way, the temperature change On the other hand, the electrical resistivity of Invar is about 36%, the electrical resistivity of nichrome is about 31%, and the electrical resistivity of brass is about 70%, whereas that of Constantan is about 8.6. % Change). When considering the operation of a superconducting magnet, considering that the liquid nitrogen temperature, which is cold, fluctuates about 1 (K) for some reason, the change in electrical resistivity should be about 10% or less compared to room temperature. Therefore, it can be said that the temperature characteristics of constantan are excellent. Constantan has a characteristic that it is hardly affected by a magnetic field as used for measuring the temperature of many superconducting magnets as, for example, a copper-constantan thermocouple.

のリファレンス抵抗が得られた。 In view of the above, it can be said that Constantan is suitable as a material for the resistance wire constituting the reference resistors R1 to R5. In the case of the reference resistor shown in FIG. 10 in the present embodiment, a constantan wire having a diameter of 0.5 (mmφ) and a length of 2 (m) is wound around an FRP rod having a diameter of 5 (mmφ) by about 127 turns without induction. The electrical resistance value

The reference resistance was obtained.

Next, a method of adjusting such reference resistors R1 to R5 to optimum values for quench detection of the superconducting magnet will be described.
Since it is difficult to adjust the reference resistances R1 to R5 during the operation of the superconducting magnet, it is necessary to perform the adjustment in a normal temperature environment. Since the superconducting wire is in a normal conducting state at room temperature, it seems that heat is easily generated when a current is passed, but by applying a high frequency alternating current, the voltage drop due to the inductance of the superconducting coil becomes larger, The voltage drop due to the resistance that causes heat generation can be substantially ignored.

  For example, in the case of a superconducting magnet composed of five superconducting coils as shown in FIG. 6, assuming that the wire resistance at room temperature in each superconducting coil is about 10Ω, the resistance of the whole superconducting coil is about 50Ω. . Even if AC power having an amplitude of 10 (V) and a frequency of 1 (kHz) is supplied to such a superconducting magnet, the current is kept at about 6 (mA) due to the large inductance of the superconducting coil, and the superconducting magnet is overheated. Will not cause any damage.

例えば、Ｒ５＝１０（Ω）とした場合、残るリファレンス抵抗は（３）式を用いて、Ｒ１＝１０．０１（Ω）、Ｒ２＝１０．２３（Ω）、Ｒ３＝１０．１８（Ω）、Ｒ４＝１０．０６（Ω）と求められる。このように常温下でリファレンス抵抗Ｒ１〜Ｒ５を適切に調整することができる。 Thus, even when the alternating current applied to the superconducting coil is small, the voltage (e1-e2, e2-e3, e3-e4, e4-e5, e5) between the superconducting coils is about 2 (V). The voltage drop due to each superconducting coil can be accurately measured and adjusted. Specifically, first, any one reference resistor (here, R5) is set, and based on this, the remaining reference resistors R1 to R4 may be adjusted as in the following equation.

For example, when R5 = 10 (Ω), the remaining reference resistances are calculated using the equation (3): R1 = 10.01 (Ω), R2 = 10.23 (Ω), R3 = 10.18 (Ω) , R4 = 10.06 (Ω). Thus, the reference resistors R1 to R5 can be appropriately adjusted at room temperature.

  By adjusting the reference resistors R1 to R5 in this way, the detection values Vm1 (t) to Vm4 (t) including noise as described above with reference to FIGS. 8 and 9 are accurately adjusted to zero voltage. Thus, calibration can be performed. Thereby, quench detection based on the detection values Vm1 (t) to Vm4 (t) can be performed under a clear reference by canceling the influence of noise.

  As described above, the quench detection device 20 according to the present embodiment can detect the quench even when the superconducting magnet is composed of three or more superconducting coils. In particular, quench detection is possible even when the superconducting coil is composed of an odd number of superconducting coils or when the superconducting magnet is composed of an even number of superconducting coils and cannot be divided into two equal groups. . Thus, the quench detection device 20 can be widely used for various types of superconducting magnets.

In the quench detection device 20, even in a superconducting magnet composed of a large number of superconducting coils, the initial setting can be easily performed by calibration taking into account the influence of the interaction between the superconducting coils, and accurate quench detection can be performed. It can be carried out. In particular, by comparing each detection value Vm1 (t) to Vm4 (t) with a change pattern prepared in advance, it is possible to easily identify which superconducting coil has caused the quench.
As described above, according to the quench detection device 20 according to the present embodiment, a bridge circuit is configured with respect to a plurality of superconducting coils constituting the superconducting magnet, and the quench phenomenon is caused based on the voltage change in the bridge circuit. It can be detected early and with high accuracy.

  The present invention can be used for a passive quench detection method for a superconducting magnet in which a plurality of superconducting coils are connected to each other in series via connection points.

3 DC power supply 4 Electric circuit 5 Detection unit 6 Ammeter 7 Voltmeter 13 First lead 14 Second lead 15 Bridge circuit 16 Voltage detection unit

Claims (6)

A superconducting magnet quench detection method in which N (where N is an integer greater than or equal to 2) superconducting coils are connected in series via a connection point,
(I) N reference resistors connected in series with each other and connected in parallel to the N superconducting coils, and (ii) connected to a connection point between adjacent superconducting coils among the N superconducting coils. (N-1) first leads, and (iii) (N-1) second leads connected to a connection point between adjacent reference resistors among the N reference resistors. A circuit configuration step of configuring a bridge circuit by incorporating the N superconducting coils into the N superconducting coils;
A voltage detection step for detecting the (N-1) first of the leads and the (N-1) the voltage between the second lead of the respective
Quenching is generated based on whether any voltage between the (N-1) first leads and the (N-1) second leads exceeds a preset reference value. A quench detection step to detect;
A combination of voltage detection values in the voltage detection step when quenching is detected in any of the N superconducting coils is prepared in advance.
And in the quench detection step, the measured value detected by the voltage detecting step, by comparing the combination of the detected values the previously prepared quench to identify the portion where the quench occurs among the N superconducting coil A method for detecting a passive quench of a superconducting magnet, comprising a generation location identifying step.   The method for passive quench detection of a superconducting magnet according to claim 1, wherein the N is 3 or more.   The combination of detection values of the voltage includes a sign of each voltage value when quenching occurs in each of the N superconducting coils. Quench detection method. When an AC current is applied to the N superconducting coils in a room temperature environment, an adjustment process is provided for adjusting the N reference resistors based on voltages generated in the N superconducting coils. The passive quench detection method for a superconducting magnet according to any one of claims 1 to 3 . Said N reference resistor is passive quench detection method of the superconducting magnet according to claim 1, any one of 4, which is a variable resistor which constantan and resistance material. The superconducting magnet passive quench detection method according to any one of claims 1 to 5 , wherein each of the N superconducting coils has a double pancake structure.

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