JPH0766986B2 - Permanent current switch device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is necessary for energizing a superconducting magnet in a permanent current mode in an apparatus using the superconducting magnet such as a superconducting magnet and a rotating machine, a magnetic resonance diagnostic device, a magnetic levitation train, an accelerator and the like. Permanent current switch device.

[0002]

2. Description of the Related Art For using a conventional superconducting magnet in a permanent current mode, a so-called permanent current switch or a superconducting switch has used a method of thermally or mechanically switching a superconducting wire. That is, the superconducting switch is arranged in parallel with the superconducting coil forming the superconducting magnet. The operation method of superconducting switch is (1) circuit connection or disconnection method by mechanical contact between superconducting wires,
(2) A method in which a heater is wound around a superconducting wire and the superconducting wire is transitioned between a superconducting state and a normal conducting state depending on whether or not the heater generates heat, or (3) A coil is wound around the superconducting wire to generate a coil. A method of transitioning a superconducting wire between a superconducting state and a normal conducting state by a magnetic field that has been used has been used. The method (1) is a mechanical method, and the methods (2) and (3) are switches that utilize the superconducting-normal conduction transition of the superconducting wire.

Documents describing this type of technology include, for example, Toichi Okada's "Cryogenic Engineering Handbook", Uchida Lao Tsurugai Shinsha, 1978, 474-47.
Page 5 is mentioned.

[0004]

However, when the conventional superconducting switch is used as the permanent current switch of the superconducting magnet, there are the following problems. That is, the mechanical switching method of the method (1) has a problem in reliability. In the case of mechanical contact, the contact pressure regulates the superconducting current flowing through the switch. However, when the superconducting wire is contacted at a low temperature such as liquid helium temperature or liquid nitrogen temperature, the adsorbed substance adheres to the surface of the wire,
A reproducible correspondence between contact pressure and superconducting critical current cannot be obtained. Further, the mechanical method has a limit in switching speed, and has a limit of millisecond level.

In the case of the superconducting switch utilizing the superconducting-normal conduction transitions of the methods (2) and (3), the reliability is high as compared with the mechanical switching method, but the switching speed is low and the level is higher than microsecond. Is.

The above-mentioned problems of the superconducting switch are common to metal-based superconducting magnets and oxide-based superconducting magnets. In the case of oxide-based superconducting magnets, there are further problems peculiar to oxides. Method (1)
In the case of the contact type, since the oxide superconducting material hardly causes plastic deformation, the contact cross-sectional area is small even when mechanically contacting. The oxide superconducting material does not show a high critical current density unless it shows a crystal structure peculiar to the superconducting phase, but it is stochastic that the contact portion forms an atomic arrangement similar to that of the superconducting crystal at the atomic layer level. For these reasons,
Even if the oxide superconducting materials are brought into contact with each other, the characteristics become like Josephson junction, and a high critical current density cannot be obtained. Therefore, it cannot be used for a persistent current switch having a high current capacity. In the cases of the methods (2) and (3), it is difficult to switch by the magnetic field because the oxide superconducting material has a high critical magnetic field of several tens of tesla. on the other hand,
Since the oxide superconducting material exhibits a critical temperature of 90 K or higher such as yttrium-based material, it takes several orders of magnitude longer time than the metal-based superconducting material to generate the normal conduction transition by heating with the heater.

The object of the present invention is to use a superconducting switch as a permanent current switch of a superconducting magnet, with stability and reproducibility, ensuring a high current level or a critical current density, and a speed of microsecond or less. An object of the present invention is to provide a permanent current switch device that can perform switching by.

[0008]

In order to achieve the above object, according to claim 1 of the present invention, an oxide-based normal conductive film is formed on an insulating substrate, and an oxide is formed on the normal conductive film. A system superconducting film is formed by stacking, and this superconducting film is divided into two regions with a small distance, one of which serves as a source electrode and the other serves as a drain electrode. The switch is provided with a superconducting switch element having a structure in which a conductive third electrode is arranged through an insulating film in a region where the superconducting film does not exist on the normal conducting film. A superconducting magnet winding made of a superconducting wire is connected in parallel between both terminals of the source electrode and drain electrode of the device to form an electrically closed circuit, and between the superconducting mode and the normal conduction mode of this electrically closed circuit. Transition above By applying voltage to the third electrode to a permanent current switch device arrangement for switching control.

According to a second aspect of the present invention, a plurality of the above-mentioned superconducting switch elements are provided, the source electrode of each switch element is connected to one source electrode common terminal via the superconducting wire, and the drain electrode is connected to the superconducting wire. To the drain electrode common terminal, and the third electrode is also connected to the one third electrode common terminal via the superconducting wire. The superconducting magnet is connected in parallel between the source electrode common terminal and the drain electrode common terminal. A permanent current switch having a structure in which windings are connected to form an electrically closed circuit, and the transition between the superconducting mode and the normal conduction mode of the electrically closed circuit is controlled by applying a voltage to the third electrode common terminal. The device.

Further, according to a third aspect of the present invention, the superconducting film is a Y-Ba-Cu-based oxide, which is an oxide having an atomic layer surface composed of Cu and oxygen atoms, and Bi-Sr-Ca-.
One of Cu-based oxide and Tl-Ba-Ca-Cu-based oxide
Of the La-Ba-Cu-based oxides, Pr-Ba-Cu-based oxides, and Bi-Sr-Cu-based oxides, which have the same atomic layer plane of Cu and oxygen atoms as the normal conductive film. A permanent current switch device, which is one of them.

Further, according to claim 4 of the present invention, the atomic layer plane composed of Cu and oxygen atoms in the normal conductive film is not perpendicular to the direction connecting the source electrode and the drain electrode composed of the superconducting film. Current switch device.

[0012]

The structure and operation method of the above-mentioned permanent current switch device are, for the reasons described below, a high current level or a critical current which is a requirement as a permanent current switch for a superconducting magnet described in the section of the problem to be solved by the invention. The density can be secured and switching can be performed at a speed of microsecond or less.

The permanent current switch device according to the present invention performs a switching operation according to the following principle. Ie Y-
When a normal-conducting thin film having the same crystal structure contacts an oxide-based superconducting thin film such as Ba-Cu oxide, the part of the normal-conducting thin film which contacts the superconducting thin film is superconducting in the submicron range from the interface. Such a phenomenon is a phenomenon peculiar to an oxide junction in which a superconducting layer and a normal conducting layer are formed with the same crystal structure. Therefore, in the electrode arrangement of the superconducting thin film in which the distance is maintained at a dimension of several microns or submicrons, the superconducting current can flow between the electrodes, or the superconducting current can flow if the distance between the electrodes is further reduced at the submicron size. In the case of the electrode arrangement in which the superconducting current does not flow, a voltage is applied to the third electrode to increase the carrier concentration in the normal conductive layer, whereby the superconducting current can be obtained. The applied voltage is set to a value required for the normal conductive layer to form the storage layer or the inversion layer. The change in carrier concentration due to the application of voltage is due to the so-called electric field effect, which utilizes the bending of the band due to the electric field in a system having a gap in the electronic structure. In the case of an electrode arrangement in which a superconducting current flows, a normal conduction state can be achieved by applying a voltage to the third electrode and decreasing the carrier concentration in the normal conduction layer. The applied voltage is set to a value necessary for the normal conductive layer to form a depletion layer.

Such a switching system has an extremely high switching speed as compared with a conventional system involving macro and equilibrium heat transfer, or a time constant associated with an inductance in a system utilizing a magnetic field generated in a coil. The reason for this is that the switching system of the persistent current switch device of the present invention corresponds to a microscopic transition between the superconducting state and the normal conducting state in the normal conducting layer. That is, the transition from the normal state to the superconducting state in the normal conducting layer is the formation process of the superconducting pair state accompanying the generation of carriers, and the transition from the superconducting state to the normal conducting state is achieved by the dissipation of the superconducting pair. These processes are determined by circuit constants such as the distance between the electrodes and the gate capacitance of the switching device, and switching is performed at a speed of nanosecond or less. In particular, when the distance between the electrodes is a fine dimension of submicron, the switching is completed in several picoseconds or tens of picoseconds.
The reason for this is that the quasi-particles in the oxide superconducting material, that is, the time when normal carriers are combined to become superconducting conductors, are 1 to 2 times.
This is because it is a picosecond and is extremely short as compared with the conventional metal-based superconducting material.

The superconducting switch element used in the present invention does not use the mode in which the switching operation is performed by the phase change of the superconducting carrier system between the electrodes, that is, the Josephson effect. The current flowing by the Josephson effect is several tens of mA or less, and even if the cross-sectional size of the element is increased, it does not increase in proportion to this and is saturated. Therefore, the Josephson current mode cannot be applied to a superconducting magnet that passes a current of tens or hundreds of amperes. However, the permanent current switch device according to the present invention does not use the Josephson current mode but controls the amplitude of the superconducting current. Therefore, the superconducting current can be increased indefinitely depending on the superconducting property of the superconducting electrode, the carrier concentration in the normal conducting layer, the ordering degree of the atomic arrangement of the Cu-O two-dimensional plane, and the like.

In order to further increase the current level in the superconducting state, the atomic layer plane of Cu and oxygen atoms in the normal conducting film, the so-called Cu-O two-dimensional plane, is parallel to the direction connecting the superconducting electrodes, or at least The atomic arrangement of the normal conducting film is not vertical. This means that the critical current density in the Cu-O two-dimensional plane in the oxide superconducting material is c
Although higher than the critical current density in the axial direction, such a phenomenon also applies to the superconducting current level in the normal conducting layer of the superconducting switch element. Needless to say, in order to further increase the current level in the present persistent current switch, a persistent current switching device having a structure in which a plurality of superconducting switch elements are connected in parallel with each other via a superconducting wire is suitable.

[0017]

EXAMPLE 1 FIG. 1 shows the structure of a superconducting switch element used in the permanent current switch device of the present invention. 1 (a) is a top view, FIG.
(B) is the AB sectional view. The oxide-based superconducting films 3 and 4 and the oxide-based normal conducting film 2 are formed on the insulating substrate 1, the normal conducting film and the superconducting film are laminated, and the superconducting film is divided into two regions. 3 and drain electrode 4
And The distance between the source electrode 3 and the drain electrode 4 is 0.
5 to 1 micrometer. 2 through normal conductive film 2
A superconducting element having a structure in which individual superconducting films are electrically connected is formed. In this superconducting element, the third electrode film 6 having conductivity is arranged in the region where the superconducting film does not exist via the insulating film 5. In this superconducting device, the insulating substrate 1 is made of strontium titanate and the superconducting films 3 and 4 are made of Ho-Ba-C.
u oxide, normal conductive film 2, Pr-Ba-Cu oxide, insulating film 5
The strontium titanate and the third electrode film 6 as A
Let u. As shown in FIG. 2, the present superconducting switch element 7
Is connected in parallel to the superconducting magnet 8 made of an oxide wire to form a permanent current switch device.
The superconducting magnet 8 is also made of an oxide superconducting wire.

The superconducting switch element 7 is manufactured by the following method. Pr-Ba-Cu oxide normal conductive film and Ho-
The Ba-Cu oxide superconducting film is formed by a reactive vapor deposition method using oxygen plasma or a high frequency magnetron sputtering method. Both the Pr-Ba-Cu oxide normal-conducting film and the Ho-Ba-Cu oxide superconducting film have crystal morphology with uniform orientation, and the c-axis of the crystal is the direction of conduction, that is, the line connecting the source and drain electrodes. The arrangement is vertical.

Pr-Ba-Cu oxide normal conductive film and Ho-Ba
-Cu oxide superconducting film after forming a laminated film, Ho-Ba-Cu
A submicron-wide groove was formed in the oxide superconducting film by electron beam drawing and ion beam etching to form a superconducting film.
The source and drain electrodes are formed by dividing into individual pieces. The strontium titanate thin film is formed by the laser deposition method. Further, the Au third electrode film is formed by the vacuum evaporation method. An ultrafine multifilamentary wire is used as the oxide wire forming the superconducting magnet 8, and the diameter of the superconducting wire is 1 micron or less. The ultrafine superconducting wire is embedded in an Ag sheath. The superconducting wire is joined to the source or drain electrode via Ag. Ag serves as a superconducting connection and an adhesive. The Au third electrode film 6 is connected to the lead wire by an ordinary metal bonding method.

An oxide-based superconducting magnet 8 is connected to the superconducting switch element 7 manufactured by the above method, and an energization test is conducted. First, when no voltage is applied to the Au third electrode film 6 of the superconducting switch element 7, the switch element is set to 1
All of the current generated from the DC power source flows through the superconducting magnet 8 due to the Milliohm resistance. While the superconducting magnet 8 is supplied with a current of 1 A, a voltage is applied to the Au third electrode film 6 of the superconducting switch element 7 to make a transition to the superconducting state. At the same time, the energization of the current source 11 is stopped. At this time, a permanent current of 1 A flows in the closed circuit connecting the superconducting magnet 8 and the superconducting switch element 7. The persistent current switch device has reproducible switching characteristics, that is, the element resistance in the voltage state and the critical current value in the zero voltage state. In addition, it is confirmed by real-time measurement that switching in a state where the superconducting magnet 8 is not connected is completed in a time of 1 microsecond or less.

Embodiment 2 FIG. 3 shows a circuit structure of a switch element of a parallel structure used in a large current capacity permanent current switch device according to the present invention. Each basic element has the sectional structure shown in FIG.
Oxide-based superconducting films 3 and 4 and oxide-based normal conductive film 2
Is formed on the insulating substrate 1, and the normal conductive film 4 and the superconducting film 3,
4 are laminated, and the superconducting film is divided into two regions, which will be the source 3 and the drain electrode 4. The distance between the source electrode 3 and the drain electrode 4 is 0.5 to 1 μm. A superconducting element having a structure in which two superconducting films are electrically connected via a normal conducting film is formed. In this superconducting element, the third electrode film 6 having conductivity is arranged in the region where the superconducting film does not exist via the insulating film 5. In this superconducting element, the insulating substrate 1 is made of magnesium oxide, the superconducting films 3 and 4 are made of Bi-Sr-Ca-Cu oxide, and the normal conducting film 2 is made of Bi.
-Sr-Cu oxide, the insulating film 5 is strontium titanate, and the third electrode film 6 is Au. As shown in FIG. 3, ten basic element structures are connected in parallel. The connection of the basic elements is made via a Bi-Sr-Ca-Cu oxide thin film. As shown in FIG. 2, terminals 3'and 4'of the present superconducting switch element are connected in parallel to the superconducting magnet 8 made of an oxide wire to form a permanent current switch device. The superconducting magnet 8 is also made of an oxide superconducting wire.

Each basic element is manufactured by the following method. Bi-Sr-Cu oxide normal conductive film and Bi-Sr-Ca
The -Cu oxide superconducting film is formed by a reactive vapor deposition method using oxygen plasma or a high frequency magnetron sputtering method. Both the Bi-Sr-Cu oxide normal conductive film and the Bi-Sr-Ca-Cu oxide superconducting film have crystal forms with uniform orientations, and the c-axis of the crystal is perpendicular to the substrate surface. After forming a laminated film of Bi-Sr-Cu oxide normal conductive film and Bi-Sr-Ca-Cu oxide superconducting film,
A submicron-wide groove is formed in the Bi-Sr-Ca-Cu oxide superconducting film by an electron beam drawing method and an ion beam etching method, and the superconducting film is divided into two to form source and drain electrodes. The strontium titanate thin film is formed by the laser deposition method. Further, the Au third electrode film is formed by the vacuum evaporation method. An ultrafine multifilamentary wire is used as the oxide wire material forming the superconducting magnet, and the diameter of the superconducting wire is 1 micron or less. The ultrafine superconducting wire is embedded in an Ag sheath. The superconducting wire is joined to the source or drain electrode via Ag. Ag
Has a role as a superconducting connection and an adhesive. Au
The third electrode film is connected to the Cu lead wire by a normal metal bonding method.

An oxide type superconducting magnet 8 is connected to the terminals 3'and 4'of the superconducting switch element having a parallel structure manufactured by the above method, and an energization test is conducted. First, when no voltage is applied to the Au third electrode film 6 of the permanent current switch device 7, the switch device 7 generates a resistance of 0.1 milliohm, and all the current supplied from the current source 11 flows to the superconducting magnet 8. With a current of 10 A applied to the superconducting magnet 8, a voltage is applied to the Au third electrode film 6 of the superconducting switch element to cause a transition to the superconducting state. At the same time, the energization of the current source 11 is stopped. At this time, the closed circuit connecting the superconducting magnet 8 and the superconducting switch element has 1
A permanent current of 0 A flows. The persistent current switch device has reproducible switching characteristics, that is, the element resistance in the voltage state and the critical current value in the zero voltage state. In addition, it is confirmed by real-time measurement that switching in a state where the superconducting magnet 8 is not connected is completed in a time of 1 microsecond or less.

The permanent current switching device shown above is used not only for using the single superconducting magnet 8 in the permanent current mode, but also for a strong magnetic field such as a rotating machine, a magnetic resonance diagnostic device, a magnetic levitation train, or an accelerator. It goes without saying that it is used to operate a device using a superconducting magnet for generating a current in the permanent current mode. Further, as described above, the permanent current switch device is connected to the oxide superconducting magnet and operated at a temperature near the liquid nitrogen temperature.

[0025]

As described in the section of the embodiments, the present invention has the following effects regarding the permanent current switch device. (1) 3 same as semiconductor transistors
Since it is a terminal element and performs switching operation between the zero voltage state, that is, the superconducting state and the voltage state, that is, the normal conducting state by the third electrode, the switching operation is stable as compared with mechanical switching or thermal switching. Yes, with reproducibility. (2) Since a switching operation is performed by applying a voltage to the third electrode and adjusting the carrier concentration, the switching speed is significantly increased as compared with mechanical switching or thermal switching, and the switching time is 1 microsecond. The following switching times are obtained: (3) Since the mechanical connection method which is disadvantageous in the oxide superconducting material is not used, the oxide superconducting material can be connected to the oxide superconducting magnet and operated at a temperature near the liquid nitrogen temperature.

[Brief description of drawings]

FIG. 1 is an embodiment view of a switch element of the present invention, (a) is a top view and (b) is an AB sectional view thereof.

FIG. 2 is a configuration diagram of a permanent current switch device according to the present invention.

FIG. 3 is a configuration diagram of a large current capacity permanent current switch according to the present invention.

[Explanation of symbols]

 1 ... Insulating substrate 2 ... Oxide normal conductive film 3 ... Source electrode 4 ... Drain electrode 5 ... Oxide insulating film 6 ... Third electrode 7 ... Superconducting switch element 8 ... Superconducting magnet winding 9 ... Low temperature container 10 ... Voltage source 11 ... Current source

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazumasa Takagi 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Akira Tsukamoto 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. (72) Inventor Masahiko Hiratani 1-280 Higashi Koikeku, Kokubunji, Tokyo Inside the Hitachi Central Research Laboratory (72) Inventor Mitsuo Suga 1-280, Higashi Koikeku, Tokyo Kokubunji City Inside the Hitachi Central Research Center (72) Inventor Masakuni Okamoto 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. An oxide-based normal-conducting film is formed on an insulating substrate, and an oxide-based superconducting film is laminated on the normal-conducting film. The superconducting film is separated by a minute distance. It is divided into two regions, one is the source electrode and the other is the drain electrode.The source electrode and the drain electrode are electrically connected through the lower normal conductive film, and the superconducting film on the normal conductive film is further connected. A superconducting switch element having a structure in which a conductive third electrode is arranged in an area not present via an insulating film, and a superconducting wire made of a superconducting wire is provided in parallel between both terminals of a source electrode and a drain electrode of the switch element. A permanent magnet characterized in that an electrically closed circuit is formed by connecting magnet windings, and a transition between a superconducting mode and a normal conduction mode of the electrically closed circuit is switching-controlled by applying a voltage to the third electrode. Electric current Switch devices. 2. A plurality of superconducting switch elements according to claim 1, wherein each switch element has a source electrode via a superconducting wire to a common source electrode terminal and a drain electrode via a superconducting wire. One drain electrode common terminal, the third electrode is also connected to one third electrode common terminal via a superconducting wire, and the superconducting magnet winding is connected in parallel between the source electrode common terminal and the drain electrode common terminal. To form an electrically closed circuit, and the transition between the superconducting mode and the normal conduction mode of this electrically closed circuit is performed by
A persistent current switching device characterized in that switching control is performed by applying a voltage to a common electrode terminal. 3. The superconducting film according to claim 1 or 2 is Cu.
Y-, which is an oxide having an atomic layer surface composed of oxygen and oxygen atoms
Ba-Cu-based oxide, Bi-Sr-Ca-Cu-based oxide, Tl
-Ba-Ca-Cu-based oxides, which are ones of the Ba-Ca-Cu-based oxides and which have the same atomic layer plane of Cu and oxygen atoms as the normal-conducting film, and La-Ba-Cu-based oxides, Pr-Ba-Cu A persistent current switch device, characterized in that it is one of a Bi-Sr-Cu-based oxide. 4. The permanent layer according to claim 3, wherein the atomic layer plane composed of Cu and oxygen atoms in the normal conductive film is not perpendicular to the direction connecting the source electrode and the drain electrode composed of the superconducting film. Current switch device.