JP6227917B2 - Active quench detection method for superconducting magnets - Google Patents

Description

  The present invention relates to a superconducting magnet active quench detection method for detecting a quench by inputting an AC signal which is an active signal in a superconducting magnet having an electric circuit configured by connecting a DC power supply in series to a superconducting coil. Technical field.

  In a device using a magnetic field 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 combined with a permanent magnet is known. The Halbach magnetic circuit generates a uniform and strong magnetic field in the center of the donut by configuring the doughnut-shaped magnetic circuit by arranging the easy magnetization axis of the permanent magnet according to the magnetic field distribution direction of the dipole magnetic field created by the permanent magnet. It is a magnetic circuit. FIG. 5 shows a configuration example of the Halbach magnetic circuit, which is configured by combining a plurality of permanent magnets 32 in a hollow housing 30, and realizes a maximum magnetic flux density B = 1.5 (T).

  Since such a Halbach magnetic circuit is configured by combining a large number of magnetized permanent magnets, it requires an enormous amount of force for its assembly, and it is therefore difficult to obtain a stronger magnetic field. Therefore, superconducting magnets have recently attracted attention as a means for obtaining a stronger magnetic field. A superconducting magnet is formed by winding a superconducting wire whose electric resistance value is substantially zero 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. .

  A superconducting magnet can generate a strong magnetic field by applying a huge current. When the superconducting magnet is operated, when the superconducting phase is suddenly destroyed and transitions to the normal conducting phase, the superconducting coil is overheated and a so-called quench phenomenon occurs that destroys (burns) the superconducting coil. In actual superconducting magnet operation, it is extremely important to avoid such a quench phenomenon. There are various causes of the quench phenomenon, but 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 is destroyed and a quench phenomenon is observed. Such a quenching phenomenon causes a serious failure such as fusing of the superconducting coil winding, so that it is required to detect it quickly and accurately.

  Various techniques have been studied for this kind of quench detection method. For example, there is Patent Document 1. Patent Document 1 discloses a method of detecting a quench by dividing a superconducting coil into a plurality of sections using voltage taps and measuring each potential difference.

JP 2012-248725 A

  A high-temperature superconducting wire called Y-based or Bi-based has a critical temperature Tc higher than that of a conventional metal superconducting wire, so that it is generally considered that a quenching phenomenon hardly occurs. However, in the superconducting magnet, the coil winding is exposed to a strong magnetic field, so that the risk of occurrence of quenching is relatively high.

  Moreover, it is common to use a tape-shaped wire for the high-temperature superconducting wire because of restrictions on the manufacturing method. When such a tape-shaped high-temperature superconducting wire is used for the coil winding, the pancake structure shown in FIG. 6 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 tape-shaped high-temperature superconducting wire has a smaller heat transfer characteristic than a wire having a substantially circular cross section due to its thinness. For this reason, when a normal conducting phase is generated, it is easy to cause a serious failure such as fusing due to heat generation, so that accurate quench detection is required at an earlier stage.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an active quench detection method for a superconducting magnet capable of detecting a quench phenomenon in a superconducting magnet early and with high accuracy.

  In order to solve the above-described problem, an active quench detection method for a superconducting magnet according to the present invention includes an electric circuit configured by connecting a DC power source in series to the first superconducting coil and the second superconducting coil, A first loop circuit connected in parallel to the electric circuit and configured by connecting a first capacitor and a first voltage detection unit in series to the first superconducting coil; and A second loop circuit connected in parallel to the second superconducting coil and connected in series with a second capacitor and a second voltage detector; and the first loop circuit, A superconducting magnet comprising: an AC signal supply unit provided on a common potential line shared at a midpoint between the first superconducting coil and the second superconducting coil in the second loop circuit. An active quench detection method for a superconducting magnet that detects quenching in the active signal, an active signal input step of inputting an AC signal having a predetermined frequency from the AC signal supply unit, and a detection value V1 of the first voltage detection unit And detecting the detected value V2 of the second voltage detecting unit and calculating the potential difference ΔV = V1−V2, and detecting the quench of the superconducting magnet when the potential difference ΔV exceeds a predetermined threshold value. And a determination step for determining that it has been performed.

  According to the present invention, an equivalent first loop circuit and second loop circuit, which are AC circuits that can be analyzed independently of a DC electric circuit provided with a DC power supply, are provided, and based on potential differences in the respective loop circuits. Thus, the quench can be detected by obtaining a minute resistance value generated by a magnetic flux flow resistance or the like closely related to the quench.

In one aspect of the present invention, the constants of the first capacitor and the voltage detector are set so that a resonance condition is established in the first loop circuit, and the constants of the second capacitor and the voltage detector are It is preferable that the resonance condition is established in the loop circuit 2.
According to this aspect, by configuring each loop circuit to be a resonance circuit, it is possible to improve the accuracy of calculation of a minute resistance value generated by a magnetic flux flow resistance or the like using approximate calculation. As a result, quench can be detected with high accuracy.

The first voltage detection unit and the second pressure detection detection unit may be resistive elements connected in series in the first loop circuit and the second loop circuit, respectively.
According to this aspect, it is possible to directly detect the voltage drop in each loop circuit with a simple configuration by measuring the potential across the resistor element.

An embodiment using a current transformer is also conceivable as a current detection method for the loop circuit. For example, the first voltage detection unit and the second pressure detection detection unit detect a current flowing through the first loop circuit and a current flowing through the second loop circuit. The potential difference ΔV may be obtained by converting the detected values of the two current transformers, the first current transformer, and the second current transformer into corresponding voltage values.
Even when current detection is performed as in this aspect, a resistor that limits the alternating current is required to prevent an infinite high-frequency current from flowing in the resonance state.

In another aspect of the present invention, in the determination step, the potential difference ΔV may be acquired as an electric signal, and the determination may be performed based on a band component corresponding to the frequency of the AC signal in the electric signal by a band pass filter. Good.
According to this aspect, the noise component included in the potential difference used for calculation of the minute resistance such as the magnetic flux flow resistance can be removed by the band pass filter. Particularly in this aspect, by removing components other than the carrier frequency band of the AC signal by the band pass filter, it is possible to eliminate noise due to the influence of the DC power source and the outside, and to detect the quench with high accuracy.

In this case, in the determination step, the determination may be performed based on an output of an amplifier that amplifies the output signal of the bandpass filter.
According to this aspect, since unnecessary noise is removed by the band-pass filter, a necessary signal can be extracted as a large signal without being buried in the noise even when amplified, so that quench is detected with higher accuracy. be able to.

The AC signal supply unit may be a transformer including a first coil to which an AC signal is input from an AC signal source and a second coil connected to the common potential line. .
According to this aspect, by inputting the AC signal through the transformer, non-contact signal input is possible, and quench detection with less noise is possible.

Moreover, you may provide the protection process which interrupts | blocks the said electric circuit automatically, when quenching is detected in the said detection process.
According to this aspect, when it is determined that there is a risk of quenching due to an increase in the minute resistance generated by the magnetic flux flow resistance or the like, by automatically shutting down the electric circuit (for example, incorporating a protection circuit or the like) Good), risk that could lead to serious breakdowns can be avoided early.

The first superconducting coil and the second superconducting coil may have a double pancake structure connected in series with each other via the midpoint.
In this aspect, since the double pancake structure is structurally easy to provide a midpoint inside the coil wound in a pancake shape as described above with reference to FIG. 6, the active quench detection method according to the present invention is used. The circuit configuration used can be easily incorporated.

  According to the present invention, an equivalent first loop circuit and second loop circuit, which are AC circuits that can be analyzed independently of a DC electric circuit provided with a DC power supply, are provided, and based on potential differences in the respective loop circuits. Thus, the quench can be detected by determining a flux flow resistance closely related to the quench.

It is a graph which shows the electric current and voltage characteristic in the external magnetic field zero of a YBCO high temperature superconducting wire. It is a schematic diagram which shows the generation principle of the magnetic flux flow resistance in a superconductor. It is the schematic which shows the whole structure of the quench detection apparatus which concerns on a reference technique. It is the schematic which shows the whole structure of the quench detection apparatus which concerns on a present Example. It is a structural example of a Halbach magnetic circuit. It is a schematic diagram which shows an example of the superconducting coil 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.

In the present embodiment, a case will be described in which superconducting coils L1 and L2 formed by winding a superconducting wire having a YBCO high-temperature superconductor, which is a high-temperature superconducting material, as a wire are used as detection targets for quenching. FIG. 1 is a graph showing the current-voltage characteristics (VI) at zero external magnetic field (self-magnetic field characteristics) of the YBCO high-temperature superconducting wires constituting the superconducting coils L1 and L2. In this example, a SuperPower YBCO high-temperature superconducting wire having a length of 500 cm and a line width of 12 mm is used, the horizontal axis indicates current (A), and the vertical axis indicates voltage (V).
As shown in FIG. 1, when the DC current flowing through the superconducting coils L1 and L2 is increased from 0A toward the critical current Ic (≈400A), the voltage starts to increase from the vicinity exceeding about 200A and from about 350A. A rapid voltage increase was confirmed. This voltage is a voltage generated by the movement of the magnetic flux in the superconducting wire, and indicates that an increase in magnetic flux flow resistance occurs as a precursor of the quench phenomenon.

FIG. 2 is a schematic diagram showing the principle of generation of magnetic flux flow resistance in the superconductor. Here, the magnetic field B is applied to the superconductor 1, and the magnetic field that has entered the superconductor 1 exists as a magnetic flux 2. The magnetic flux 2 is pinned to a defect or the like existing in the superconductor 1 when the current flowing through the superconductor 1 is very small. On the other hand, when a large current I is passed through the superconductor 1, the pinned magnetic flux 2 receives a Lorentz force F in a direction orthogonal to the current I and the magnetic field B as shown in FIG. As the magnitude of the current I is further increased, the Lorentz force F also increases, and the magnetic flux 2 begins to move out of pinning at a timing exceeding a certain threshold. At this time, a voltage ΔE is generated by the magnetic flux flow, and equivalently, a magnetic flux flow resistance of r = ΔE / I (current is an energization current) is generated, and q = rI ^{2 in} the superconductor 1 due to the magnetic flux flow resistance. An exotherm occurs.
At this time, if the superconducting coil is not sufficiently cooled, the superconducting wire causes an increase in equivalent resistance due to the generated heat, and is finally observed as a quench phenomenon of the superconducting magnet.

の電圧が生じることとなる。この電圧は数Ｖであるため、数〜数１０μＶ程度の磁束フロー電圧を分離して検出することは難しい。 In principle, the magnetic flux flow resistance in the superconducting coil may be measured by simply detecting the voltage across the superconducting coil. However, in an actual superconducting magnet, there is a problem that it is difficult to detect quenching because a drive DC power supply and noise from the outside exist, and a voltage signal due to a minute magnetic flux flow resistance is buried.
Further, quenching of the superconducting magnet often occurs while the power supply current is being increased. At this time, assuming that the inductance of the superconducting coil is L at both ends of the superconducting coil and the current supplied from the DC power source to the superconducting coil is i (t), in addition to the magnetic flux flow resistance at both ends of the superconducting coil,

Will be generated. Since this voltage is several volts, it is difficult to separately detect a magnetic flux flow voltage of about several to several tens of μV.

  The superconducting magnet active quench detection method according to the present invention aims to solve such problems. In the present embodiment, the detection apparatus 10 for carrying out the active quench detection method will be described in detail later. First, a reference technique that is a prerequisite for the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram showing the overall configuration of the quench detection apparatus 10 ′ according to the reference technique.

(Reference technology)
The superconducting magnet that is the detection target of the quench detection apparatus 10 ′ according to the reference technology is configured as a double pancake type by connecting the superconducting coils L1 and L2 having a pancake structure in series (see FIG. 6). Superconducting coils L1 and L2 have the same inductance. In the superconducting coils L1 and L2, an electric circuit 4 is formed in which a DC power source 3 operable with a commercial power source is connected in series. In FIG. 3, a DC current flowing through the electric circuit 4 is indicated by Idc. The magnitude of the direct current Idc is controlled by a power supply controller (not shown) according to the magnitude of the magnetic field generated in the superconducting coils L1 and L2.

When a current is passed from the electric circuit 4 to the superconducting coil and the current is increased, the voltage VL due to the inductance and the voltage Vr due to the resistance r generated by the magnetic flux flow appear in the superconducting coil as the total voltage Ec.

The electric circuit 4 is provided with a noise compensation coil L ₀ (coil composed of normal conducting wires) on one end side of the superconducting coils L1 and L2. Since the coil L ₀ is a normal conducting wire, it has a finite resistance rn. When the current increases, the coil L ₀ appears as a total voltage E ₀ of the inductance voltage VL ₀ and the finite resistance voltage Vrn in the coil L ₀ like the superconducting coil.

ここでＬ１、Ｌ２、Ｌ₀は既知量なので、微分項ｄＩ_dc／ｄｔの係数をゼロになるように差動増幅器６の増幅率Ａ₀、Ａｃを調整する事が出来る。従って、差動増幅器６の出力は電流Ｉ_dc に比例した電圧

となる。補償コイルＬ₀の線抵抗も事前に調べることができ既知量になるので、最終的に差動増幅器６の出力ΔＶは超電導コイルの磁束フロー等で発生した抵抗ｒに比例した値となる。このようにして、超電導コイル内に発生する磁束フロー等の微小抵抗ｒを検出する事ができる。 In the differential amplifier 6 amplifies the voltage from the compensation coil L ₀ by an amplifier 7 for amplifying the gain Ao, the voltage of the superconducting coil may be amplified by the amplifier gain Ac of the amplifier 8, the subtracting these voltages, by the following formula The voltage shown appears as the output of the differential amplifier 6.

Here, since L1, L2, L ₀ is a known quantity, it is possible to adjust the amplification factor A _0, Ac of the differential amplifier 6 so that the coefficient of differential term dI _dc / dt to zero. Therefore, the output of the differential amplifier 6 is a voltage proportional to the current I _dc

It becomes. Since the line resistance of the compensation coil L ₀ can be examined in advance and becomes a known amount, the output ΔV of the differential amplifier 6 finally becomes a value proportional to the resistance r generated by the magnetic flux flow of the superconducting coil. In this way, a minute resistance r such as a magnetic flux flow generated in the superconducting coil can be detected.

Thus, in the quench detection apparatus 10 ′ according to the reference technique, it is possible to determine whether or not a quench has occurred with a certain degree of accuracy. However, it is impossible to detect the L1, L2, L ₀ and minute resistance r of the magnetic flux flows like rn occurs precisely beforehand determined not when the superconducting in the coil. Furthermore, since a large current is passed through the compensation coil L ₀ composed of a normal conducting wire, there is enormous heat generation, and the merit of using the superconducting coil is impaired, so the feasibility is extremely poor.
In the embodiment described below, it is possible to solve such a problem of the reference technique.

  FIG. 4 is a schematic diagram illustrating the overall configuration of the quench detection device 10 according to the present embodiment. In the following description, parts that are the same as those described above are denoted by the same reference numerals, and redundant description is omitted as appropriate.

  The quench detection device 10 is intended for detection of a superconducting magnet having an electric circuit 4 configured by connecting a DC power supply 3 in series to the superconducting coils L1 and L2. The electric circuit 4 is provided with a first loop circuit 11 and a second loop circuit 12 which are AC circuits in parallel. In particular, the first loop circuit 11 and the second loop circuit 12 are configured such that the common potential line 14 is shared at the midpoint 13 between the superconducting coils L1 and L2 having a double pancake structure.

  A capacitor C1 and a resistor R1 are connected in series to the first loop circuit 11, and a capacitor C2 and a resistor R2 are connected in series to the second loop circuit 12. The capacitors C1 and C2 and the resistors R1 and R2 use the same elements, and the first loop circuit 11 and the second loop circuit 12 are configured to be equivalent.

  A transformer 16 is provided on the common potential line 14, and a sine wave AC signal having a constant amplitude generated by the signal generation source 15 is input via the transformer 16. The transformer 16 is configured to include a first coil 16 a connected to the signal generation source 15 and a second coil 16 b connected to the common potential line 14, and an AC signal is sent to the first loop circuit 11. And functions as an interface for input to the second loop circuit 12. In this embodiment, by using the transformer 16 as an AC signal input interface in this manner, non-contact signal input is possible, and quench detection with less noise is possible.

Here, since the first loop circuit 11 and the second loop circuit 12 which are AC circuits have capacitors C1 and C2, respectively, the DC current Idc flowing through the electric circuit 4 is the first loop circuit 11 and the second loop circuit 12. Only the electric circuit 4 is circulated without flowing through the second loop circuit 12.
On the other hand, since the elements (resistors R1 and R2 and capacitors C1 and C2) included in the first loop circuit 11 and the second loop circuit 12 are set to be equal, the superconducting coils L1 and L2 Both end voltages are equipotential to each other. Therefore, the AC signal supplied to the first loop circuit 11 and the second loop circuit 12 circulates through the first loop circuit 11 and the second loop circuit 12, respectively, without flowing through the electric circuit 4. Become.
As described above, the detection circuit included in the detection device 10 is configured such that the DC circuit and the AC circuit can be analyzed independently of each other.

  The voltage drops in the resistors R1 and R2 are taken out as voltage signals V1 and V2 and input to the differential amplifier 6. The differential amplifier 6 outputs a difference ΔV between the voltage signals V1 and V2. As a result, when an increase in magnetic flux flow resistance associated with the quench phenomenon occurs in any of the superconducting coils L1 and L2, it is detected as ΔV.

  The output ΔV of the differential amplifier 6 is input to a bandpass filter 18 having a band corresponding to the frequency f = f0 of the AC signal. Since various frequency noises are included in the input signal from the differential amplifier 6, extraneous noise can be removed by extracting the frequency (carrier frequency) of the AC signal by the band-pass filter 18. . In particular, since the DC power source 3 that is a driving power source for the superconducting magnets L1 and L2 often generates large voltage noise, a minute magnetic flux flow voltage tends to be buried in the noise. Therefore, in the present embodiment, the noise included in the detection signal is removed by the bandpass filter 18 so that accurate quench detection can be performed.

ここでｒは超電導コイルＬ１あるいはＬ２で発生した磁束フロー抵抗を示しており（尚、図４では超電導コイルＬ２側に磁束フロー抵抗ｒが生じた場合を例示している）、変圧器１６のインピーダンスは十分に小さく無視できると仮定する。また、Ｍは超電導コイルＬ１_、及びＬ２間の相互インダクタンスであり、磁気結合係数Ｋを用いて

と表わされる。 The output signal of the band-pass filter 18 is input to the detection unit 19 that calculates the magnetic flux flow resistance. Here, the AC signal supplied to the common potential line 14 is a continuous sine wave having an amplitude e0 and a frequency f (each frequency ω = 2πf). If the alternating currents flowing through the first loop circuit 11 and the second loop circuit 12 are i ₁ (t) and i ₂ (t), respectively, the following alternating equations are obtained.

Here, r represents the magnetic flux flow resistance generated in the superconducting coil L1 or L2 (in FIG. 4, the case where the magnetic flux flow resistance r is generated on the superconducting coil L2 side is illustrated), and the impedance of the transformer 16 Is sufficiently small and negligible. Further, M is the mutual inductance between the superconducting coils _L1, and L2, using magnetic coupling coefficient K

It is expressed as

（５）式に示す連立方程式を解くことにより、第１のループ回路及び第２のループ回路を流れる交流電流Ｉ_１及びＩ_２が得られる。 When the equation (4) is Fourier transformed, the following equation is obtained.

By solving the simultaneous equations shown in the equation (5), the alternating currents I ₁ and I ₂ flowing through the first loop circuit and the second loop circuit are obtained.

が成立する。この場合、抵抗Ｒ_１及びＲ_２における電圧降下Ｖ_１及びＶ_２は、次式により求められる。

Here, assuming that the first loop circuit 11 and the second loop circuit 12 are in a resonance state,

Is established. In this case, the voltage drops V ₁ and V _{2 at} the resistors R ₁ and R ₂ are obtained by the following equation.

と仮定すると、（５）式の分母はｒを無視して

と近似できるので、差動アンプ６の出力ΔＶは次式により求められる。

Here, the magnetic flux flow resistance r is very small.

Assuming that the denominator of equation (5) ignores r

Therefore, the output ΔV of the differential amplifier 6 can be obtained by the following equation.

The expression (7) shows that the output ΔV of the differential amplifier 6 is proportional to the magnetic flux flow resistance r. Since E ₀ is the amplitude of the AC signal, ΔV is also an AC signal. In this way, since the magnetic flux flow resistance is obtained as an AC signal in this embodiment, even when amplified by an amplifier, it can be amplified without being affected by the drift of the amplifier.

  By the way, the noise from the DC power supply 3 and the outside is considered to be applied to the first loop circuit 11 and the second loop circuit 12 which are equivalent to each other at the same time and in the same phase. Is offset by Further, as described above, ΔV is analyzed by extracting the carrier frequency by the band pass filter 18, so that the minute magnetic flux flow resistance r can be accurately detected.

  The detection unit 19 determines whether or not there is a quench in the superconducting coils L1 and L2 based on whether or not the magnetic flux flow resistance r thus obtained is larger than a predetermined threshold value r1. The threshold value r1 is set as a magnetic flux flow resistance that suggests the occurrence of quenching. For example, the VI characteristic shown in FIG.

  When the magnetic flux flow resistance r exceeds the threshold value r1 (r> r1), the detection unit 19 activates the protection circuit 20 provided in the DC power source 3 to interrupt the operation of the superconducting magnet and protect it. At this time, if the power supplied to the superconducting coils L1 and L2 is suddenly cut off, a large counter electromotive force is generated due to the electromagnetic induction action, so that it is preferable to control so as to attenuate gradually.

に基づいて、超電導コイルＬ１及びＬ２の総インダクタンスＬは１２．５（ｍＨ）となり、それぞれのインダクタンスＬ１及びＬ２は６．２５（ｍＨ）となる。また磁気結合係数をＫ＝１とすると、相互インダクタンスは

となる。 Subsequently, the case where the present invention is applied to SMES (Superconducting Magnet Energy Storage), which is an application example of a superconducting magnet, using the above-described quench detection device 10 will be specifically verified. Here, SMES energy is, for example, E = 1000 (J) on a laboratory scale, and DC current Idc flowing through superconducting coils L1 and L2 is 400 (A). In this case, inductance calculation formula

Therefore, the total inductance L of the superconducting coils L1 and L2 is 12.5 (mH), and the respective inductances L1 and L2 are 6.25 (mH). If the magnetic coupling coefficient is K = 1, the mutual inductance is

It becomes.

を成立させるために、コンデンサＣ１及びＣ２は、それぞれ０．０８８（μＦ）とする。また抵抗Ｒ１及びＲ２は１０（Ω）とし、交流信号の振幅をＥ₀＝１（Ｖ）とした場合、磁気フロー抵抗ｒとして１００（ｎΩ）が超電導コイルＬ２に発生したと仮定すると、（６）式により、ΔＶは約１０（ｎＶ）の交流電圧として検出される。ΔＶは差分電圧なので超電導コイルＬ１及びＬ２に対して同位相で入り込んだノイズは互いに相殺される。一方で、不平衡なノイズは相殺することができないが、バンドパスフィルタ１８を介して検出部１９に取り込むことで、キャリア周波数以外をカットすることができる。またΔＶは交流信号であるので増幅器で増幅させたとしても、増幅器のドリフトによる影響を回避することができ、良好な精度でクエンチを検出できる。
例えばΔＶを１００００倍に増幅することで、磁束フロー抵抗ｒ＝１００（ｎΩ）を０．１（ｍＶ）の検出信号として得ることができるので、一般的なデジタルボルトメータでも測定が可能となり、コストを抑えることができる。 Further, as the AC signal output from the signal generation source 15, the frequency f = 42.414 (Hz) may be selected in order to reduce the influence of noise from the DC power source 3 that operates on the commercial power source. In this case, the resonance condition in the first loop circuit 11 and the second loop circuit 12

In order to establish the above, capacitors C1 and C2 are each set to 0.088 (μF). Further, assuming that the resistances R1 and R2 are 10 (Ω) and the amplitude of the AC signal is E ₀ = 1 (V), it is assumed that 100 (nΩ) is generated in the superconducting coil L2 as the magnetic flow resistance r (6 ) Is detected as an AC voltage of about 10 (nV). Since ΔV is a differential voltage, noises entering the superconducting coils L1 and L2 in the same phase cancel each other. On the other hand, unbalanced noise cannot be canceled out, but by capturing the unbalanced noise in the detection unit 19 via the bandpass filter 18, it is possible to cut other than the carrier frequency. Since ΔV is an AC signal, even if it is amplified by an amplifier, the influence of drift of the amplifier can be avoided and quench can be detected with good accuracy.
For example, by amplifying ΔV by 10,000 times, a magnetic flux flow resistance r = 100 (nΩ) can be obtained as a detection signal of 0.1 (mV), so that measurement can be performed even with a general digital voltmeter. Can be suppressed.

の発熱が発生すると、保護回路２０を作動するように制御する。 The threshold r1 for quench detection in the detection unit 19 is preferably set to about several μΩ. If the threshold value r1 is set to 1 (μΩ), since the direct current is 400 (A) as described above, in the superconducting coil L2,

When the heat generation occurs, the protection circuit 20 is controlled to operate.

  As described above, in the detection apparatus 10 according to the present embodiment, the equivalent first loop circuit 11 and second loop circuit that are AC circuits that can be analyzed independently of the DC electric circuit 4 provided with the DC power supply 3. Quench can be detected by providing a loop circuit 12 and determining a flux flow resistance closely related to the quench based on the potential difference in each loop circuit.

例えば、超電導線の線臨界電流密度をＪｃ＝１０（ＭＡ／ｍ）程度とし、超電導線幅をａ＝４（ｍｍ）とする。本実施例では、交流電流の振幅Ｉｍ＝１００（ｍＡ）であるから、超電導線で発生する交流損失は１０^−５（Ｗ／ｍ）程度である。超電導コイルに使用される超電導線の全長が５００（ｍ）であるとすると、超電導マグネット全体での交流損失は５（ｍＷ）であり、無視できる程小さな値となる。
尚、更に交流損失を小さく抑えたい場合には、交流電源の電圧を更に下げればよい。 In the detection apparatus 10 according to the present embodiment, since an AC signal flows through the superconducting coils L1 and L2, it is necessary to pay attention to an AC loss peculiar to the superconductor. AC loss can be expressed as energy loss per cycle. For example, according to the Superconducting Handbook (published by the Institute of Electrical Engineers of Japan), the AC loss P / f is assumed that the amplitude of the AC signal Iac is Im, the critical current density of the superconducting wires constituting the superconducting coils L1 and L2 is Jc, and the sample region is a. Is obtained by the following equation.

For example, the line critical current density of the superconducting wire is set to about Jc = 10 (MA / m), and the width of the superconducting wire is set to a = 4 (mm). In this embodiment, the alternating current amplitude Im = 100 (mA), so the alternating current loss generated in the superconducting wire is about 10 ⁻⁵ (W / m). If the total length of the superconducting wire used for the superconducting coil is 500 (m), the AC loss in the entire superconducting magnet is 5 (mW), which is a negligibly small value.
In order to further reduce the AC loss, the voltage of the AC power source may be further reduced.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a superconducting magnet active quench detection method for detecting quench in a superconducting magnet having an electric circuit configured by connecting a DC power source in series to a superconducting coil.

DESCRIPTION OF SYMBOLS 3 DC power supply 4 Electric circuit 6 Differential amplifier 11 1st loop circuit 12 2nd loop circuit 13 Midpoint 15 Signal generation source 16 Transformer 18 Band pass filter 19 Detection part

Claims (6)

An electric circuit configured by connecting a DC power source in series to the first superconducting coil and the second superconducting coil;
A first loop circuit that is connected in parallel to the electrical circuit and is configured by connecting a first capacitor and a first voltage detection unit in series to the first superconducting coil;
A second loop circuit connected in parallel to the electric circuit, and configured by connecting a second capacitor and a second voltage detection unit in series to the second superconducting coil;
An alternating-current signal supply unit provided on a common potential line shared at a midpoint between the first superconducting coil and the second superconducting coil of the first loop circuit and the second loop circuit; A superconducting magnet active quench detection method for detecting quenching in a superconducting magnet comprising:
An active signal input step of inputting an AC signal having a predetermined frequency from the AC signal supply unit;
Obtaining a detection value V1 of the first voltage detection unit and a detection value V2 of the second voltage detection unit, and calculating a potential difference ΔV = V1−V2;
A determination step of determining that quenching of the superconducting magnet is detected when the potential difference ΔV exceeds a predetermined threshold ,
The constants of the first capacitor and the voltage detector are set so that a resonance condition is established in the first loop circuit,
Active quench detection method of a superconducting magnet constant of the second capacitor and the voltage detection unit is characterized that you have been set so that the resonance condition is satisfied in the second loop circuit.   An electric circuit configured by connecting a DC power source in series to the first superconducting coil and the second superconducting coil;
  A first loop circuit that is connected in parallel to the electrical circuit and is configured by connecting a first capacitor and a first voltage detection unit in series to the first superconducting coil;
  A second loop circuit connected in parallel to the electric circuit, and configured by connecting a second capacitor and a second voltage detection unit in series to the second superconducting coil;
  An AC signal supply unit provided on a common potential line shared at a midpoint between the first superconducting coil and the second superconducting coil of the first loop circuit and the second loop circuit;
A superconducting magnet active quench detection method for detecting a quench in a superconducting magnet comprising:
  An active signal input step of inputting an AC signal having a predetermined frequency from the AC signal supply unit;
  Obtaining a detection value V1 of the first voltage detection unit and a detection value V2 of the second voltage detection unit, and calculating a potential difference ΔV = V1−V2;
  A determination step of determining that quenching of the superconducting magnet is detected when the potential difference ΔV exceeds a predetermined threshold;
With
  The AC signal supply unit
  An active quench detection of a superconducting magnet, characterized in that it is a transformer comprising a first coil to which an AC signal is input from an AC signal source and a second coil connected to the common potential line. Method.   The first voltage detection unit and the second voltage detection unit are resistance elements connected in series in the first loop circuit and the second loop circuit, respectively. 3. The active quench detection method for a superconducting magnet according to 2.   The determination step is characterized in that the potential difference ΔV is acquired as an electric signal, and a determination is made by a band pass filter based on a band component corresponding to the frequency of the AC signal. The active quench detection method for a superconducting magnet according to any one of the above. The determination if the quench in the process is detected, the active quench detection of the superconducting magnet according to claim 1, any one of 4, characterized in that it comprises a protection step of automatically interrupting the DC power supply Method. It said first superconducting coil and the second superconducting coil according to any one of claims 1 to 5, characterized in that it comprises a double pancake structure connected in series through the midpoint to each other Active quench detection method for superconducting magnets.

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