JPS6159650B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for charging a superconducting magnet coil using a rectifying flux pump method. When a superconducting magnet coil is used in persistent current mode, it is initially necessary to force a large current, for example, several thousand amperes, through the coil by some means. In order to pass the large current through the superconducting magnet coil, a lead wire with a large diameter is provided by penetrating the cryogenic chamber, and the current is forcibly supplied to the coil from the outside through this lead wire.
This is not preferable as it allows external heat to enter the inside of the cryogenic chamber. For this reason, generally, a power transformer with an iron core is installed in a cryogenic chamber, and by using this transformer, the diameter of the lead wire is made small, and charging is performed by reducing the introduction of external heat. There is.
As an example of such a charging means, the following rectifying flux pump system has conventionally been implemented. FIG. 1 is a schematic diagram showing a conventional rectifying flux pump. The area surrounded by a dashed line 1 in the figure is a cryostat maintained at an extremely low temperature.Inside the cryostat 1, there is a primary winding 3 wound around an iron core 2 and a secondary winding having a midpoint tap. An iron-core power transformer 5 consisting of wires 4 is housed therein. Each of the above windings 3 and 4
are each made of superconducting wire, and the primary winding 3
is connected to an applied voltage waveform controller 6 provided outside the cryogenic chamber 1. Further, the center tap of the secondary winding 4 is connected to one end of the superconducting magnet coil 7. The other end of this coil 7 is connected to one end of the secondary winding 4 via a current reversal detector 8a and a switch 9a.
b and the other end of the secondary winding 4 via switch 9b. Further, each detection signal of the current reversal detectors 8a, 8b is given to the applied voltage waveform controller 6, and the command signal from this controller 6 is given to the switches 9a, 9b, respectively. As shown in FIG. 2, the primary winding 3 has _positive ,
Zero, negative, zero, positive, zero, second charging cycle period
Voltage that becomes negative, zero, positive, zero, negative, zero at T ₂
P ₁ is applied. By repeating these first and second charging cycle periods T ₁ and T ₂ alternately, the superconducting magnet coil 7 is so-called charged. That is, it is assumed that the first charging cycle is started with the switch 9a being OFF and the switch 9b being ON. First, as shown in FIG. 2, at the start time _t1 of the first charging cycle period _T1 , a positive pulse voltage + is applied to the primary winding 3 as shown by _P1 in the same figure.
When E ₁ (direction of arrow A) is applied, current R ₁ flows in the winding 3 in the direction of arrow A, and this primary current R ₁
increases at a constant rate. For this reason, the secondary winding 4
The secondary induced voltage Q ₁ is +α ₁ as shown in Figure 2.
(in the direction of arrow B). Therefore, current flows in the direction of arrow C through the closed loop including superconducting magnet coil 7 and switch 9b, and coil 7 is charged. When the primary applied voltage P ₁ is made zero at time t ₂ when the iron core 2 is not yet saturated, the secondary induced voltage Q ₁ becomes zero because the primary current R ₁ maintains a constant value. Then, according to the program preset in the applied voltage waveform controller 6, the switch 9a is turned on at time _t3 and the primary applied voltage _P1 is set to _-E2 , so that the secondary induced voltage _Q1 becomes -α ₂ (in the opposite direction of arrow B), and a short circuit current in the direction of arrow D flows in the closed loop including switches 9a and 9b. During this process, the charging current _S1 of the magnet coil 7 decreases slightly. When the current in the direction of arrow D becomes slightly larger than the charging current _S1 at time _t2 , the detector 8b outputs a current reversal detection signal. Due to this detection signal, the primary applied voltage _P1 becomes zero at time _t4 , and the switch 9b is turned off. In this case,
The charging current _S1 flowing through the magnet coil 7 is in the direction of arrow E including the switch 9a. Next, when the primary applied voltage P ₁ is set to +E ₁ again at time t ₅ , the secondary induced voltage Q ₁ is +α ₁ and in the direction of arrow B, so the charging current S ₁ of the magnet coil 7 increases at a constant rate. Decrease. That is, the coil 7 will be discharged. Then, at time t ₆ when the iron core 2 is saturated, the secondary induced voltage Q ₁ rapidly decreases to zero. As a result, the charging current _S1 of the coil 7 is reduced, that is, the discharging is stopped. Further, at the above-mentioned time _t6 , the primary applied voltage _P1 is maintained at zero. The above is the first charging cycle, and the second charging cycle is performed from the end time _t7 of the first charging cycle with the primary applied voltage _P1 having a polarity opposite to that of the first charging cycle. Thus,
The charging current _S1 of the superconducting magnet coil 7 will increase cumulatively. However, since such a conventional method uses a power transformer 5 with an iron core, it is necessary to set the discharge time in the first and second charging cycle periods T ₁ and T ₂ in consideration of the saturation magnetic flux of the iron core 2. . For this reason, there were problems such as the charging time of the superconducting magnet coil 7 becoming longer and the operation of charging the coil 7 becoming extremely complicated. Furthermore, since the iron core 2 is used, there are drawbacks such as hysteresis loss and an increase in the size of the entire device. The present invention was made in consideration of the above circumstances, and
The purpose is to provide a method for charging superconducting magnet coils that can be easily charged without using an iron core in the transformer, without causing hysteresis loss, or increasing the size of the entire device. be. That is, the present invention achieves the above object by using an air-core superconducting transformer to charge a superconducting magnet coil in an operation close to an ideal form. An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a schematic diagram showing an example of a rectifying flux pump to which the method of the present invention is applied.
Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. This embodiment uses an air-core superconducting transformer 1 instead of the conventional iron-core power transformer 5 .
0, and the other configuration is exactly the same as that shown in FIG. Now, switch 9a is OFF and switch 9b is off.
Assume that it is in the ON state, and as shown in Fig. 4, the primary applied voltage _P2 is positive, zero, negative, and zero during the first charging cycle period _T1 , and the primary applied voltage P2 is set to positive, zero, negative, and zero during the second charging cycle period T1.
These first and second as negative, zero, positive, zero at T ₂
Repeat the charging cycle alternately. First, at time t ₁ at the beginning of the first charging cycle period T ₁ , a positive pulse voltage +E ₁ is applied to the primary winding 3 as indicated by P ₂ in the figure.
(in the direction of arrow A), the primary current R ₂ increases at a constant rate, and the secondary induced voltage Q ₂ becomes +α ₁ (in the direction of arrow B). In this case, switch 9a
Since the switch 9b is OFF and ON, a current flows in the closed loop including the superconducting magnet coil 7 and the switch 9b in the direction of arrow C, and this current increases at a constant rate. Therefore, the charging current _S2 of the superconducting magnet coil 7 increases from zero at a constant rate. Then, according to the program preset in the applied voltage waveform controller 6, the primary applied voltage _P2 is made zero at time _t2 and the switch 9a is turned on, and then the primary applied voltage _P2 is turned on at time _t3 . −E ₂ . Note that the period t ₂ -t ₃ is the time required for the switch 9a, which is a superconducting switch called a cryostron, to change from normal conductivity to superconductivity. Period t ₂ −
At _t3 , the primary current _R2 is a constant value and the secondary induced voltage _Q2 is zero, so the charging current of the superconducting magnet coil 7 is constant. The primary applied voltage P ₂ becomes −E ₂ at time t ₃
Then, the primary current R ₂ decreases at a constant rate, and the secondary induced voltage Q ₂ becomes −α ₂ . In this case, since the switches 9a and 9b are both ON, a short circuit current flows in the direction of arrow D in the closed loop including the switches 9a and 9b. And this short circuit current is at time t ₂
When the charging current S becomes slightly larger than ₂ ,
Current reversal detector 8b outputs a current reversal detection signal. This detection signal activates switch 9b at time _t4 .
When turned off, the primary applied voltage _P2 becomes zero.
Note that the charging current _S2 of the superconducting magnet coil 7 decreases slightly during the period _t3 - _t4 . Moreover, after time _t4 , the charging current _S2 of the coil 7 is changed to the switch 9a.
It flows in the direction of arrow E through a closed loop including Then, the switch 9b completely transitions to normal conductivity at time _t5 . The above is the first charging cycle. Then, the final time t ₅ of the first charging cycle period T ₁
starts the second charging cycle. That is _, when the primary applied voltage P 2 is set to -E ₁ at the first time t ₅ of the second charging cycle period T ₂ , the primary current R ₂ decreases at a constant rate and the secondary induced voltage Q ₂ becomes -α ₁ (in the opposite direction of arrow B). In this case, since the switch 9a is ON and the switch 9b is OFF, the current due to the voltage _-α1 flows in the direction of the arrow E in the closed loop including the superconducting magnet coil 7 and the switch 9a. Therefore, the charging current of superconducting magnet coil 7
S ₂ increases at a constant rate. Then, at time _t6 , the primary applied voltage _P2 is reduced to zero and switch 9b is turned on.
After turning ON, the primary applied voltage P ₂ is set to +E ₂ at time t ₇ . As a result, a short circuit current flows in the direction of arrow D in the closed loop including the switches 9a and 9b, and when this short circuit current becomes slightly larger than the charging current _S2 at time _t6 , the detector 8a outputs a current reversal detection signal. do. This detection signal causes switch 9 to switch at time _t8 .
When a is turned off, the primary applied voltage _P2 is held at zero. Then, the second charging cycle period _T2 ends at time _t9 when the time for the switch 9a to transition to normal conductivity has elapsed. Thus, by repeating the first and second charging cycles alternately, the charging current _S2 of the superconducting magnet coil 7 increases cumulatively, and the coil 7 is charged. . Note that the superconducting magnet coil 7 is discharged by performing the reverse operation of the above-described operation by setting the primary applied voltage _P2 to the opposite polarity. Thus, according to the present invention, an air-core superconducting transformer
The superconducting magnet coil 7 is charged and discharged using the above-described method using the superconducting magnet coil 10 . Since charging and discharging can be performed in a nearly ideal manner, the charging and discharging operation can be greatly simplified without considering the saturation magnetic flux of the iron core, etc. Further, since no iron core is used, there are advantages such as eliminating hysteresis loss and reducing the weight of the entire device, that is, reducing the size of the device. moreover,
Since the device configuration can be almost the same as the conventional one by simply changing the transformer, it is very convenient for implementation. Note that the present invention is not limited to the embodiments described above. For example, in the air-core superconducting transformer, the primary winding may be wound in a toroidal manner, and the secondary winding may be wound on the toroidal winding.
Furthermore, it goes without saying that the magnitude, application time, etc. of the primary voltage may be determined as appropriate depending on the specifications of the superconducting magnet coil. Further, the application time may be set using a counter, CR integrator, or the like. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a rectifying flux pump using the conventional method, Fig. 2 is a signal waveform diagram to explain the effect during charging by the same method, and Fig. 3
The figure is a schematic configuration diagram showing a rectifying flux pump as an embodiment to which the method of the present invention is applied, and FIG. 4 is a signal waveform diagram for explaining the operation of the embodiment. 1...Cryogenic chamber, 2...Iron core, 3...Primary winding,
4... Secondary winding, 5 ... Power transformer, 6... Applied voltage waveform controller, 7... Superconducting magnet coil, 8a, 8b... Current reversal detector, 9a, 9b
...Switch, 10 ...Air-core superconducting transformer.

Claims (1)

[Claims] 1. Connect one end of a superconducting magnet coil to the middle point of the secondary winding of an air-core superconducting transformer kept at an ultra-low temperature, and connect both ends of the secondary winding to the magnet coil through a switch and a current reversal detector, respectively. a means for cumulatively charging the magnetic coil by alternately repeating a first charging cycle and a second charging cycle by turning the switch on and off when a current reversal is detected; The voltage applied to the primary winding of the superconducting transformer is varied in the order of positive, zero, negative, and zero during the first charging cycle period, and in the order of negative, zero, positive, and zero during the second charging cycle period. 1. A method for charging a superconducting magnet coil, characterized in that the method is combined with means for controlling charging of the magnet coil to charge the magnet coil.