DE1464416B2 - SUPRAL CONDUCTING COIL WITH A MULTI-LAYER WINDING - Google Patents

Description

1 2

The invention relates to a superconducting coil with operation converted to the normally conductive state

one of several, electrically insulated from each other.

A superconducting wire is used to conduct a coil Wire which winds a coating from one, the coil does not generally conduct the normally conductive one Metal has. 5 same amount of current as the wire in short lengths.

The possibility of magnetic fields not only from high Long ends of a wire from a 25 per cent

Strength, but also for a long time zirconium alloy with a diameter of

To be able to generate is for exploring the 0.25 mm lead a current of approximately 20 amps

Physics of the solid state of aggregation, of the plasma up to approximately 60,000 Gauss, whereby the current-carrying

and the particle of great importance. However, the capacity is not increased if that

In most cases, however, the production field had to be weakened so far. The difference between the

generation of large magnetic field strengths impulse fields current carrying capacities with long and short

be used. Since then, however, new supra-wire ends become less noticeable when the

conductive materials are available, the zirconium content is increased,

a considerable interest in the development of 15 The useful critical magnetic field in a

Usable magnets that have a large field strength alloy of 25% zirconium and 75% niobium

and have dimensions equivalent to about 60,000 gauss for an alloy

Make areas of application suitable in which large with a content of 33% zirconium by approximately

Magnetic field strengths are required. 5000 to 10,000 Gauss higher. It has been reported that '

As an example of the use of such magnets, 20 50 percent zirconium alloys are even stronger

be the generation of electrical power that shielding-critical fields have.

protection against radiation of charged particles, plasma is part of a current-carrying super-

drove, physical experiments on a large scale conductive wire in the normally conductive state, so

mentioned. The generation of permanent magnet- a voltage drops on this part of the wire,

fields of great strength and within large volumes 25 and energy is consumed. Is that consumption

represents an important technical task. sufficiently large, this can lead to a change in the

Recent developments in the field of the hard superconducting state of the wire or to a

Superconductors showed the possibility of great field strength destruction of the wire by melting it. is

ken generating superconducting field coils, including those on the normally conducting part with an insulated wire

to pull. The possibility of using 30 of the wire dropping voltage sufficiently high

of field coils with superconductors for the generation so the insulation can break down and envinnerer

caused by field strengths of 50,000 gauss or more with only a short circuit. This can become a

low power consumption for cooling, sparking and the formation of hot spots.

ren without Joule losses obviously offers advantages. If the short circuit is of a longer duration, then

for continuously operating power plants and the like, the current distribution in the coil changes with it

The properties of superconductors were caused by the fact that the magnetic field in the coil is at

treated differently, e.g. B. in "Superfluids", Vol. I, concentrated subsequent excitations. This is un-

by Fritz London, published in New York in 1950, desired because a local concentration of the

by John Wiley & Son, Inc., and "Superconduc magnetic field a reduction in performance due to '

tivity «by D. Shoenberg, published 1952 in 40 of the lower current carrying capacity at high

London by Cambridge University Press. Field strengths caused.

A superconductor can be made of a metal, a Le- If, on the other hand, there is a short circuit in the coil,

or a connection. Depending on the one that opens during power-up, this is how it is

Composition of the superconductor occurs the super- synonymous with a sudden switch-on

conductive state at a certain temperature 45 of a previously unused part of the coil. Because of

below 18 ° K. Substances with a higher or higher level of close coupling can do this

transformation temperature are still lead to part of the coil in the normalconducting

not found. The temperature at which the state is set.

Transition into the superconducting state takes place, the energy in some proposed large

is called the critical temperature. 50 superconducting coils is stored is several

The superconductivity of a given material megajoules. From H. KoIm et al., “High Magnetic

can be destroyed by exposure to energy fields, "The MIT Press and John Wiley, & Sons,"

in the form of heat, at which the material is New York 1962, pages 361, 362, it is known that

critical temperature reached, in the form of a magnetic because of the high energy density of the magnetic field

field, whereby the critical field strength is reached, 55 the energy released by the collapsing

or in the form of an electric current, the field in the case of spatially strongly extended coils this

critical current is reached. The critical order of magnitude can assume. Then the

Temperature, the critical magnetic field and the critical breakdown of the magnetic field for example

Amperages are all interdependent. by increasing the temperature and thus by excess

When designing superconducting coils, the normal conducting state of the superconducting

make sure that wire is made for the coil at temperature or even by breaking the

The liquid helium opens up a cryogenic circuit and thus interruption of the current

Provided that materials used are effected in this way. Because of the very big one

that is within the desired temperature resistance R is the time constant LIR of the circle

areas, currents and magnetic fields superconductive 65 small, and the breakdown of the field is explosive

tending properties show and that a protection for consequences.

the winding is provided if one or more of R. H. Kropschot and V. Arp, »SuperTeile the coil when switched on or in normal conducting magnets ", Cryogenics, Volume 2, No. 1, Sep.

3 4

1961, p. 11, it is known to protect the supra- Fig. 3 is a diagram of a superconducting coil

conductive coil parallel to the coil a resistor with a shunt circuit,

stand to switch or the coil with a copper F i g. 4 shows a somewhat different schematic representation

To surround the tube, the inductive coil with a superconducting coil with the protective circuit

is coupled and part of the energy of the 5 according to FIG. 3,

collapsing magnetic field. F i g. 5 a schematic representation of a supra-

From the French patent 1 299 456 is conductive coil with an inductive protective circuit,

a multilayer superconducting coil is known, in Fig. 6 a section through a superconducting coil,

which the superconducting wire has a plating from which the flux distribution in an inductively protected

Gold, a normal conducting metal, and shows io coil,

in which between the individual winding layers Fig. 7 a partly schematic and partly

insulation is provided. The gold plating diagrammatic representation of a superconducting coil,

acts as a shunt for the superconducting wire. which has some features according to the invention,

The disadvantage of this coil is that the gold plate and the

on the superconducting wire only when there is a schematic representation of current densities as an internal shunt. Another circuit for closing the current-Furthermore, it is disadvantageous that due to the coating circle of an inductive shield,
of the turns of the superconducting wire with WieausderFig. 1, which is a schematic representation of a low resistance metal of a conventional circuit for generating a tall the turn-on time constant becomes large. 20 constant magnetic field, it can be seen, is on

From the publication “High Magnetic Fields”, the terminals 12, 13 of a superconducting coil 14

P. 335, it is also known that a power shunt 11 is connected between the win-

applications and arranged between the layers of a superconducting the elements in an insulating vessel 15

Coil insulation is provided. are that z. B. is filled with liquid helium,

The object of the invention is therefore to provide means and measures to increase the required low temperatures which are indicative of damage to a person. A current superconducting coil is connected to a current source 16 with a heater made of a superconducting wire, which is connected to a superconducting wire, wound around the other electrically insulated layers. The current shunt 11 consists of a coating of normally conductive metal, through which 30 of a superconducting material. The heating element stored in the magnetic field of the coil consists of a non-superconducting material, if a part of such a coil is prevented during and therefore remains at all times in the normalconductive state when switched on or in operation in the normalconductive state. The main power source 21 transitions to a changing state. Licher current limiting resistor 22 and a main object of the invention is that switches 23 are connected in series with each other and solves that an insulating material is arranged between the windings with which the superconducting coil 14 and the currents within each layer that the winding - shunt 11 comprehensive parallel connection,
development in sections through outside the coil The first step in the commissioning of the lying resistors is bridged and that the interconducting coil 14 consists in the closing of some or between all layers of inductive 40 switches 18 for the heating element and the main shields in the form of electrically conductive switch 23. The current flows through the heating element foils or sheets are attached. 19, the power shunt 11 is above its

According to a further development of the invention, the critical temperature can also be heated and has

therefore, there is normal resistance between the layers and between the turns. For this

Insulation to be applied within the layers can basically be the current from the main power source

be made that flow on the normal conducting 21 through the superconducting coil 14 and this

Coating the superconducting wire excite an insulating. After energizing the coil 14, the

Layer is arranged. Switch 18 for the heating element open, so that the

The invention achieves that the superconducting shunt 11 can cool down

tend coils in applications where large 50 and superconducting. According to this, the head

Magnetic field strengths are required in large volumes, switch 23 is opened, with the current as before

that can be safely operated that the supra- through the coil 14 and the current bypass foot 11

Conductive coils do not take an inordinately long time for this to flow. Is where the superconducting coil and its

Switching on require that the coil winding do not shunt a series circuit

protected, if part of the coil is present in the nor- 55 resistor, the current flows infinitely

The conductive state returns, and that long continues, and there is no disappearance of the

magnetic energy without damaging the Wick magnetic field. However, it is for some reason

ment can be derived, if the coil in which a resistor is present, the current disappears

normal conducting state is transferred. and thus the magnetic field with a time constant,

The invention will now be ^{explained with reference} to the total resistance of the circuit

examples of management explained. In the drawings it depends. If desired, the power source 16,

Fig. 1 is a diagram of a superconducting coil of the resistor 17, the heating element 19 and the

and the associated conventional circuit for current shunt 11 is omitted and the coil 14

Generating a permanent magnetic field from which the power source 21 is constantly supplied with power

F i g. 2 is a diagrammatic representation of a part ⁶ 5.

a coated superconducting In the case of a superconducting coil made of ent wire, with a portion of the coating cut away - neither a coating-less superconducting wire ten, or from a wire that only has a coating

i 464 4iö

5 6

For a better clarity exhibiting a low resistance, the electricity material carries (no insulation), there is the substitute source and the current switch according to FIG. 1 disconnection from an inductor, which is left by a klei-. As shown in FIG. 3 can be seen, there is a resistor short-circuited. As a result, the coil has the superconducting coil 14 according to the illustration from a very large time constant. 5 the sections 14 α to 14 d, to which the small such a coil is against damage wäh- resistors 24 to 27 are correspondingly parallel schalrend of the shutdown due to the occurrence of a tet. The size of the sections 14 α to 14 d can be fully protected in the normal conducting area, since they are variable, and these either do not include any significant voltages can develop - less or more than one layer of the coil. From this, because every point on the inductor with every other io, it can be seen that the superconducting coil 14 is in point connection and not individual, divided into several sections, the currents of which consist of inevitable inductances, which depend on each Section next to a resistor at this must be discharged. closing resistance to the value zero absin-Although there is a protection during the shutdown, ken can. The shunt resistors divide the coil into sections because of the very large time constants 15 so that the energy per coil does not exceed the required switch-on time excessively section a permissible value that is long. The time constant is roughly proportional to the diameter of the design and the operating conditions of the coil to the cube of the power used to determine the coil. The number of sections, which is why the switch-on time even for small connections or shunts, is determined very quickly by the maximum energy permissible per section. The arrangement grows. the shunt resistances inside the coil

The measure of winding the superconducting wire first is less desirable than outside of the

with a coating of a low resistance coil because of the energy dissipation within the

stood exhibiting material and then made a winding.

High Resistance Material to 25 There are distinct benefits to using a conductive or shunt. The net circuit outside the coil has a satisfactory effect on the voltages generated on a normal part when the coil sections are inductively decoupled small number of bobbins located; however, if there is resistance, as the low resistance 3 ° increases the inductive coupling between the coils per unit length in the normally conducting state, a collective inductive slowdown in the resistance increase occurs. ₍ leads and thus to a slower fading time. This phenomenon is best described in the art. The coating with a lower resistance is shown in FIG Shows the shape of a spiral in which the same state flows for a longer time than if sections 14 a to 14 d were not present due to the shunt of the coating. Resistors 24 to 27 are connected to one another,

The external coating made of a material which resistors are preferably arranged outside the one-coil with a large resistance improves the one-coil. The arrows indicate the switching time requirements. Because of the excessively long 40 current flow through the coil winding. If a superconducting wire with either a bare (without any part of the most inner section of the coating) or such a 14 α changes to the normally conductive state, then with just a coating of a metal with one of the current flowing through the section 14 α decreases On-time connected to low resistance from the value zero, and the current flowing previously through the can the advantages of a superconducting wire 45 section 14 α is only used by the shunt 24 with a coating of a metal with a furthest inner shunt 24 because of the low resistance, if sen low resistance compared to the metal with a very good insulating in the normally conductive state is coated with a very good insulating part abgematerial, such as. B. nylon and poly- conductors. During the transition period the angrentetrafmoräthylen seeks. 5 ° zende section 14 b with the shunt 25 his

The F i g. 2 shows a superconducting wire 31, current due to the inductive coupling between

the one with a coating of a metal 32 with the sections or layers, depending on the location of the

is provided with a low resistance which, in its case, has to be doubled. Since the section 14 b supra-

On the one hand, a coating made of an insulating material 33 is conductive and very likely in the vicinity of the

carries a high resistance. If a critical current value is operated from the wire 55, "the

31 in the conventional manner a winding with a current flowing through the section 14 b on the

Number of turns forming several layers increased critical value, so that the section 14 b

produced, and goes a portion of the wire 31, goes into the normal conducting state. The third

for example, between the interrupted section 14 c, which previously opposed the operations in

Lines 35 and 36 should be located in the normally- ^6o first or most inner section

the state over, the metal coating 32 represents 14 α shielded by the second section 14 b

If, among other things, an electrical shunt was connected, suddenly a three-fold amperage must be applied

lead to such a section or several in order to keep the flow constant. Under the-

Sections if necessary. Under these circumstances, the third section 14c must be included

The F i g. 3 shows a circuit with shunt ^{resistors 6} 5 which are necessary in the normally conductive state, but which preferably do not go with them. This cumulative process is repeated outside the coil and / or in all sections of the coil winding as necessary. The location can be placed in a cryogenic environment. It is therefore noticeably worsening, and in the

Coil winding can induce much stronger currents than those originally flowing with the As a result, higher voltages occur and more energy is destroyed per unit length than it is would be the case if all sections were not inductively coupled to one another. Becomes a senior Protective circuit used, care must obviously be taken to ensure that the above-described collective and inductive processes are avoided.

We shall now describe the means and devices which make up the collective and inductive Prevent behavior.

5 shows the principle of the inductive protective circuit. In Fig. 5 is a normal conducting State located area 41 shown, which with a superconducting coil 14 in series is connected, which coil is inductively coupled to a protective circuit 42, the one with a normally conducting resistor 44 in series-connected coil 43 comprises. Occurs in the superconducting circle 45 according to FIG. 5, a region 41 which is in the normally conductive state, and the To dwindle magnetic flux, the protective circuit 42 seeks to keep the flux constant, so that the superconducting Circle 45 can release its energy with very little effort. Then the discharges Protection circuit 42 with the time constant of the protection circuit itself. The measure effected by the protection circuit 42 the protection depends on the coupling coefficient between the two circles as well as on their relative Time constants.

Since the coils are easily accessible inside and outside, inductive can be used without difficulty Shields e.g. made of sheet metal or foils of a non-magnetizable material with a low Resistance can be provided to reduce the energy consumed in the windings themselves on a to keep small value. In other words, the shields prevent the Current flow in the coil windings due to the inductive coupling during the transition periods.

This effect is shown in FIG. 6 shown, as an example, a superconducting coil 14 with an inner cylindrical inductive shield 51 and an outer inductive shield 52 shows which Shields made of a suitable sheet metal or foil, e.g. B. made of copper. The initial flow distribution for the coil during normal operation is shown by the solid line 53. Kick now a point with normally conducting properties, and the current in the windings drops rapidly to the value zero compared to the time constant of the inductive shields, so distributed After this initial transition, the flow changes to the broken line 54. As from FIG. 6 As can be clearly seen, the flux distribution outside the inductive shields 51 and 52 is the same immediately after the initial transition as during normal operation, whereas the flux distribution remains constant through the windings and does not increase. For a coil winding, whose outer radius is twice the inner radius and which is inductively protected, is the energy to be destroyed in the windings during the aforementioned initial transition only 13% of the energy stored in the coil winding.

This energy loss can be reduced even further if inside the winding Further shields can be provided at intervals. For example, in addition to the inner and outer shield an inductive shield between each layer of the coil winding to be ordered.

Let us now look again at the collective, inductive behavior that occurs during the transition to the normally conductive state if only the conductive protective circuit according to FIGS. 3 and 4 is used, with particular reference being made to FIG. It now turns out that the main difficulty lies in the fact that when the first section 14 α changes to the normally conducting state, the second section 14 b has to double its current in order to keep the flow constant. If, however, a thin inductive shield made of a highly conductive material such as copper is provided between the sections 14 α and 14 b , then the copper shield, which consists of a sheet metal or a foil, can be dimensioned so that it covers most of the increase in current absorbs, which was previously required for the second section, the accumulative, inductive propagation of the normally conducting area is halted. Since the energy in the copper shielding is evenly distributed in the> outer ■ volumes, the thermal

see disturbance of the outer sections kept small. The reproduction of the normal conducting State of the current district can be halted entirely, in which case the rest of the district Part of the coil is discharged through the shunt (s), namely at the one in the normally conducting State with a very large time constant that is equal to the total inductance of the superconducting coil divided by the resistance value of the shunt at the normal conducting District is.

Fig. 7 shows, as an example, a superconducting coil which has some features according to the invention having. According to this, several (three) are very conductive, non-magnetizable and cylindrical Shields 61 to 63 are provided, e.g. B. made of copper, between a number of layers 64 of the superconducting coil are arranged. For the sake of clarity, the isolation vessel has been made lind the power switch omitted. As can be seen from Fig. 7, there are three layers 64 of the superconducting Coil trapped between adjacent inductive shields. The number of these from the The layers enclosed in shielding can be one to more than three layers. Any shield is cut to create adjacent and longitudinal ends, which are connected in series with the relevant switches 65 to 67 and the resistors 71 to 73. At the longitudinally spaced ends of each shield are the short-circuit switches 74 bis connected. As in connection with FIG. 3, there are between the layers of the coil winding described, the shunt resistors 77 switched to. As already explained, look for the shields 61 to 63 to keep the total flow constant for a given period of time and the to Shutdown to slow down the required time and keep it as long as possible. The switch-off time indicates the

greatest value when the shields of switches 74 to 76 are short-circuited, or if on the other hand these are not cut and therefore a short-circuit path for the induced current represent. This arrangement leads to the greatest heating of the copper shields inside the coil, which in certain cases may not be desirable. It can therefore be in others In some cases, it may be desirable to arrange the resistors 71 to 73 outside the coil or the insulating vessel, as in FIG. 7 shown.

The use of resistors 71 to 73 increases and decreases the resistance in the inductive circuits their effect. However, the resistances provided in the inductive circuits allow outside the coil, a derivative of a substantial proportion of that in the inductive shields energy induced during shutdown. The value of this resistance should be high in comparison to that of the inductive shields, but not so high that the current is significantly limited, which can flow in the shields. As noted, on the other hand, the resistance in the inductive circuits are omitted, and the shields can be manufactured in one piece so that they form a short-circuit path for the induced current.

The effect of the inductive shields is of utmost importance when the superconducting Material is operated in the vicinity of its critical point, d. H. of the point at which a small amount of additional current creates such a strong flux that the superconducting material enters the normal conducting state passes. Due to the in the inductive shields during the When the induced current is switched off, the shields try to keep the total flow constant and prevent it thereby a changeover of the superconducting material to the normally conducting state.

The presence of the inductive shields not only facilitates the disconnection of a superconducting one Coil, but also causes thermal insulation between the layers of the coil at temperatures in which the superconducting state is stable. Furthermore, together with the inductive Shields or shunt resistors can be used with advantage diodes. As in 8 shown as an example, the resistors and the inductive shields according to FIG. 7 assigned switches can be replaced by diodes. For example, Fig. 8 shows a diode 85, which is connected in series with member 86, which is an inductive shield or section should represent the coil winding.

Therefore, each inductive circuit and / or shunt resistor can have one or more Diodes should be equipped, which are polarized so that they the current flow during switching off a low Oppose resistance and a high resistance during switch-on. This is easy to carry out as the current flows in the opposite direction when switched on as when Switch off. As is easy to see, z. B. Diodes in the inductive circuits and automatically Immediately set the desired resistance in the inductive circuits without the need for switches, sensors and the like. must be provided.

On the basis of the above, experts will recognize without difficulty that Instead of the diodes, a mechanical equivalent can be provided, as shown in FIG. 9 shown. Thereafter, the diode of Fig. 8 was replaced by a switch 91, which is either by hand or can be operated automatically with the aid of a suitable sensing device 92, either a small resistor 93 or a large resistor 94 with member 86 depending on the conditions is connected in series in the coil and / or the power supply to the coil. The in Fig. 9 The arrangement shown doubles the effect of the diode in FIG. 8.

Although a fairly short if finite amount of time is required for the current to flow into one defective section is passed to the next section via a shunt resistor, so is in the absence of inductive shielding, if the ■ segment following the defective segment is in the vicinity of its critical value, the increase in the current flow is so great that this Section is converted to the normally conductive state, etc. through the entire coil. As already noticed, the inductive shields seek to keep the total flow constant and sen to ensure that the flow diminishes to a permissible and safe extent.

If the triggering time for the inductive shields long enough, and are provided between adjacent shields a plurality of sections, as shown in FIG / 7, zo takes each section (or * each layer), only a corresponding portion of the current on, which otherwise in the or would flow to the sections adjacent to the damaged section. In this way, the possibility that an adjacent section changes to the normally conducting state is substantially reduced. Since the entire coil is no longer in the superconducting state when a normally conductive region is present, the current must flow through a resistor (through the shunt resistance at the coil section which is in the normally conductive state), whereby the entire coil is switched off to a permissible extent , ie that the coil is neither damaged nor destroyed.

During turn-off, a small amount of data stored in the coil winding energy in the superconductive material and its coating and a substantial amount of energy in the shunt resistor is destroyed at the defective portion, -during the remainder in the inductive shields and / or any downstream _i resistors is consumed.

The effect exerted on a superconducting coil by the protective measures according to the invention consists in slowing down the transitions in the coil. This means that the switch-on time is extended the more protection Go is offered. The time constants of the coils according to the invention depend on the particular structure of the coil and can therefore not be specified. For example but the time constant for a coil with an inner diameter of 127 mm is the one Field strength of 50,000 Gauss generated, on the order of ten seconds. The switch-on time of a Coil must be several times the time constant of the coil in order to generate heat in

to keep the protective devices small, as already explained. Overheating of the protective devices is doubly harmful. Firstly, it causes the helium to evaporate and, secondly, it generates heat in the immediate vicinity of the windings. As the specific heat of materials at low Temperatures is extremely small, the generation of even a small amount of heat can cause a Heat part of the windings above their critical temperature so that the coil is in the normal conducting state is transferred. The switch-on times for a coil of the type mentioned above and according to the invention can be expected to be on the order of an hour or two or less.

Claims (4)

Patent claims: 1. Superconducting coil with a layer consisting of several layers that are electrically insulated from one another Winding made of a superconducting wire, which is covered with a normal conductive Metal, characterized in that within each layer between the windings gene an insulating material is arranged that the winding in sections through outside the Coil lying resistors (24 to 27; 77 to 82) is bridged and that between some or inductive shields (61 to 63) in the form of good electrical conductivity between all layers Foils or sheets are attached. 2. Superconducting coil according to claim 1, characterized in that the inductive Shields are designed as closed cylindrical surfaces. 3. Superconducting coil according to claim 1, characterized in that each inductive Shielding (61 to 63) designed as a cylindrical surface cut open along a surface line is and that a resistor is provided to complete the circuit, which ' a large one during a flux increase in the coil and one during a flux decrease assumes small value. 4. Superconducting coil according to claim 1, characterized in that on the normal conducting Coating (32) of the superconducting wire (31) an insulating layer (33) is arranged. 1 sheet of drawings