Cryostat with magnet arrangement which includes an LTS portion and an HTS portion

Abstract

A cryostat includes a magnet arrangement for the generation of a magnetic field B0, the magnet arrangement comprising an LTS portion having at least one LTS section made from a conventional low-temperature superconductor and an HTS portion having at least one HTS section made from a high-temperature superconductor. The HTS portion is arranged radially within the LTS portion, and the cryostat is designed to control the temperature of the LTS portion and the HTS portion independently of one another, wherein the HTS portion is electrically isolated from the LTS portion, and is designed to be superconductingly short-circuited. The invention proposes a cryostat with magnet arrangement which enables a high magnetic field strength in a compact space and, at the same time, can be easily constructed.

Claims

1. A cryostat having a magnet arrangement for the generation of a magnetic field B0, wherein the magnet arrangement comprises: a low-temperature superconductor (LTS) portion having at least one LTS section made from a conventional low-temperature superconductor; and a high-temperature superconductor (HTS) portion having at least one HTS section made from a high-temperature superconductor and being arranged radially within the LTS portion, wherein the cryostat is designed to control the temperature of the LTS portion and the HTS portion independently of each other, and wherein the HTS portion is electrically isolated from the LTS portion and is configured to allow it to be superconductingly short-circuited.

2. The cryostat according to claim 1, wherein the HTS portion has no current feed lines.

3. The cryostat according to claim 1, wherein the LTS portion can be short-circuited by means of one or more superconducting switches.

4. The cryostat according claim 1, wherein the at least one HTS section comprises a closed superconducting cylindrical sleeve or one or more closed superconducting rings in a radial layer.

5. The cryostat according to claim 4, wherein said radial layer is deposited on a cylindrical support body.

6. The cryostat according to claim 1, wherein at least one HTS section comprises a coil section which is wound in the form of a solenoid with a tape conductor and is superconductingly short-circuited.

7. The cryostat according to claim 1, wherein the LTS portion comprises at least two LTS sections, including an LTS main section and an LTS shield section.

8. The cryostat according to claim 7, wherein the magnet arrangement has a plurality of charging connections with which the at least two LTS sections can be charged with electrical current and discharged independently of one another.

9. The cryostat according to claim 7, wherein the at least two LTS sections each generate a different magnetic field characteristic.

10. The cryostat according to claim 1, wherein the cryostat forms a first, outer helium tank for the LTS portion and forms a second, inner helium tank for the HTS portion.

11. The cryostat according to claim 10, further comprising a radiation shield arranged between the first helium tank and the second helium tank.

12. The cryostat according to claim 1, wherein the cryostat forms a helium tank for the LTS portion, wherein the HTS portion is arranged in a vacuum chamber which also contains the helium tank, and wherein the HTS portion can be thermally coupled to and decoupled from the helium tank by means of a heat switch.

13. A method for charging the magnet arrangement of a cryostat according to claim 1, the method comprising: a) cooling the LTS portion below a transition temperature T.sub.c,LTS and holding the HTS portion above a transition temperature T.sub.c,HTS; b) charging at least a first LTS section to an interim current I.sub.IN, wherein the interim current I.sub.IN differs from a first operating current I.sub.B.sub.1; c) cooling the HTS portion below its transition temperature T.sub.c,HTS; and d) changing a current I.sub.LTS.sub.1 in at least the first LTS section to the first operating current I.sub.B.sub.1, as a result of which the HTS portion is inductively charged.

14. The method according to claim 13, wherein, during step (b), the LTS portion overall is charged with the same interim current I.sub.IN and, during step (d), the LTS portion overall is changed to the same first operating current I.sub.B.sub.1.

15. The method according to claim 13, wherein the magnet arrangement has at least two LTS sections and a plurality of charging connections with which the at least two LTS sections can be charged with electrical current and discharged independently of one another, and wherein, in step (b), at least one second LTS section is, in turn, charged to a second operating current I.sub.B.sub.2, and wherein, in steps (c) and (d), the current I.sub.LTS.sub.2 of the at least one second LTS section is maintained at the second operating current I.sub.B.sub.2.

16. The method according to claim 15, wherein the operating currents I.sub.B.sub.1 and I.sub.B.sub.2 are different.

17. The method according to claim 13, wherein the at least one first LTS section comprises an LTS shield section of the magnet arrangement, and wherein, in step (b), the interim current I.sub.IN has an opposite sign to the first operating current I.sub.B.sub.1 in step (d).

18. The method according to claim 13, wherein the magnitude of the interim current I.sub.IN is greater than the first operating current I.sub.B.sub.1, and, in step (d), the magnitude of the current I.sub.LTS.sub.1 is reduced to the first operating current I.sub.B.sub.1 without changing a sign of the current I.sub.LTS.sub.1.

19. The method according to claim 13, wherein, after step (c), the LTS portion and the HTS portion are held at substantially the same temperature.

20. The method according to claim 13, wherein the LTS portion is, in turn, superconductingly short-circuited in an additional step (e).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is shown in the drawings and is explained in more detail with reference to exemplary embodiments. In the drawings:

(2) FIG. 1 shows a schematic diagram of the magnet arrangement of a first embodiment of a cryostat according to the invention with entirely serially connected LTS portion;

(3) FIG. 2 shows a diagram of the characteristic parameter with respect to time of a first variant of a method according to the invention for charging the magnet arrangement of FIG. 1;

(4) FIG. 3 shows a schematic diagram of the magnet arrangement of a second embodiment of a cryostat according to the invention having two separately chargeable and separately short-circuitable LTS sections;

(5) FIG. 4 shows a diagram of the characteristic parameter with respect to time of a second variant of a method according to the invention for charging the magnet arrangement of FIG. 3;

(6) FIG. 5 shows a schematic sectional diagram of a cryostat according to the invention in a third embodiment having two completely separate helium tanks without interposed radiation shield;

(7) FIG. 6 shows a schematic sectional diagram of a cryostat according to the invention in a fourth embodiment having two completely separate helium tanks with interposed radiation shield;

(8) FIG. 7 shows a schematic sectional diagram of a cryostat according to the invention in a fifth embodiment having two helium tanks which are connected to one another by means of an overflow valve;

(9) FIG. 8 shows a schematic sectional diagram of a cryostat according to the invention in a sixth embodiment having a heat switch;

(10) FIG. 9 shows a schematic, partially sectioned diagram of an HTS section for the invention having a cylindrical support body on which a plurality of HTS cylinder sleeves are deposited radially on top of one another;

(11) FIG. 10 shows a schematic, partially sectioned diagram of an HTS section for the invention having a cylindrical support body on which a plurality of radial layers of HTS rings are deposited;

(12) FIG. 11 shows a schematic diagram of an HTS section for the invention having HTS tape wound in the form of a solenoid and having an HTS-HTS joint which is superconductingly short-circuited;

(13) FIG. 12 shows a schematic diagram of an HTS section for the invention having HTS tape wound in the form of a solenoid and superconductingly short-circuited made from a slotted tape conductor.

DETAILED DESCRIPTION

(14) A basic idea of the present invention is, in the case of a magnet arrangement of a cryostat, in particular in the case of an NMR magnet, to arrange the HTS section or the HTS sections (overall HTS portion, also HTS coil) electrically and thermally insulated from the LTS section or the LTS sections (overall LTS portion, also background magnet or LTS coil). Furthermore, the cryostat is designed to charge the HTS section(s) inductively via the LTS section(s). Means for the inductive charging of the HTS section(s) can be provided for this purpose. To this end, in some embodiments, the facility is provided of charging an LTS shield coil optionally with or in opposition to an LTS main coil.

(15) Furthermore, according to the invention, the HTS coil or HTS section can be made from tape material, or also (preferably) designed as an arrangement of one or more superconducting rings or cylinders in which a current is introduced inductively during the charging process.

(16) In addition, a method for inductively charging the HTS coil is described, in which, on the one hand, the LTS coil or the LTS main section is operated in overcurrent mode at different temperatures of LTS and HTS portion. Alternatively, for the charging process, the LTS shield section for the charging process is charged so that the B0 component of the magnetic field in the bore of the cryostat is intensified and the stray field is increased. Subsequently, the HTS coil is cooled below the transition temperature, and the magnetic field of the outer LTS section(s) is reduced and current is passed through the LTS shield section such that the stray field is reduced.

(17) Within the framework of the invention, the temperature of the HTS coil, which is located, for example, in a separate helium tank from the LTS coil, is generally changed only for the charging process; superconductivity in the HTS is switched off and on by increasing and reducing the temperature above/below the transition temperature (critical temperature) of the HTS. For this reason, the temperature change also takes place in a comparatively large frame. As a rule, the temperature of the HTS coil must be controlled between approx. 4 K (or also 2 K) and approx. 100 K which can make structural differences (e.g. additional radiation shields) compared with conventional cryostats necessary or at least advantageous.

(18) Basic Types of Cryostats and Charging Process

(19) FIG. 1 shows a first embodiment of a magnet arrangement 1 of a cryostat according to the invention. The magnet arrangement 1 comprises an LTS portion (background magnet, LTS coil) 2, here with two (first) LTS sections 11, namely an outer LTS shield section (shield coil) 3 and an inner LTS main section (main coil) 4, and an HTS portion (HTS coil) 5, here comprising an HTS section 6, namely a superconductingly closed cylindrical sleeve. It is to be noted that, in practice, the sections 3, 4 and/or 6 can in each case also consist of serially connected sub-coil sections.

(20) The magnet arrangement 1 is designed to be substantially rotationally symmetrical with regard to a coil axis SA, wherein, for simplification, only the left-hand part of the section of the magnet arrangement 1 is shown in FIG. 1 (also applies to subsequent figures).

(21) The LTS portion 2 radially encompasses the HTS portion 5. In normal operation, by means of the magnet arrangement 1, a homogenous magnetic field B0, in which NMR and/or MRI measurements can take place, is generated in the direction of the coil axis SA in a test volume 7, through which the coil axis SA runs centrally. The test volume 7 lies in the room temperature bore of the cryostat. The homogeneity in the test volume 7 is typically 10 ppm or better.

(22) In the embodiment shown, the two (first) LTS sections 11 or 3, 4 respectively are connected electrically superconductingly in series and current can pass through them collectively via the external current feed lines (charging connections) T1, T2 from a power supply 9, wherein the current flowing through the current feed lines T1, T2 can be controlled and in particular varied with the power supply 9. Between the charging connections T1, T2, the LTS portion 2 as a whole can be superconductingly short-circuited by means of a superconducting switch (main switch) 8.

(23) The HTS portion 5 has no external current feed lines. The closed cylindrical sleeve of the HTS section 6 is always superconductingly short-circuited (assuming an adequately low-temperature) so that circulating currents around the coil axis SA are possible.

(24) As the HTS portion (the HTS coil) 5 has no direct electrical connection to the LTS portion (the background magnet) 2 and also has no persistent switch, the HTS coil 5 must be charged inductively. Such a charging process is described by way of example in the following: The background magnet 2 is cooled and charged while the HTS coil 5 is still held above its transition temperature T.sub.c,HTS. The background magnet 2 is overcharged, i.e. a current which lies above the nominal operating current I.sub.B.sub.1 is set. This is possible with NMR magnets as, in general, the operating current I.sub.B.sub.1 is chosen to be very much lower than the critical current I.sub.c in order to keep the magnet drift small. However, this is not relevant during the charging process. The temperature of the HTS coil 5 is now reduced until it is superconducting. The current in the background magnet 2 is now reduced to the operating current I.sub.B.sub.1. In doing so, current is induced in the HTS coil 5. By suitable design of the magnet arrangement 1, it is possible for the magnetic field B0 in the bore to increase during this process. The main switch 8 is now closed (persistent mode).

(25) In FIG. 2 the characteristic parameter with respect to time of the current I.sub.LTS.sub.1 in the background magnet 2, the temperature THTS of the HTS coil 5, the temperature T.sub.LTS of the LTS coil 2 and the characteristic parameter with respect to time of the magnetic field B0 in the bore are in each case plotted upwards against time to the right.

(26) In a first phase between t0 and t1 the current I.sub.LTS.sub.1 is brought from zero to an interim current I.sub.IN with the power supply 9 on the charging connections T1, T2. In doing so, the magnetic field B0 increases. In the meantime, the temperature T.sub.LTS of the LTS portion 2 is already below the (lowest) critical temperature T.sub.c,LTS (with NbTi approx. 10 K, with Nb.sub.3Sn approx. 15 K), here at 4.2 K. The temperature THTS of the HTS portion 5 still lies above the transition temperature T.sub.c,HTS (with YBCO approximately 92 K), here approximately 100 K.

(27) Between t1 and t2 the temperature T.sub.HTS of the HTS portion 5 is then reduced below its transition temperature T.sub.c,HTS here likewise to approximately 4.2 K. In doing so, the current I.sub.LTS.sub.1 is held constant at I.sub.IN with the power supply 9.

(28) Finally, between t2 and t3, the current I.sub.LTS.sub.1 in the LTS portion 2 is reduced from I.sub.IN to I.sub.B.sub.1 by the power supply 9; in doing so, the sign (current direction) of the current I.sub.LTS.sub.1 is not changed. The magnetic flux of the LTS portion 2 is partially transferred to the radially smaller HTS coil 5, as a result of which the field strength B0 in the test volume 7 increases.

(29) The superconducting switch 8 can then be closed and the power supply 9 can be switched off and/or removed.

(30) Selective Charging/Discharging of Certain Sections

(31) In the background magnet, one coil section can be charged independently of the remaining magnet. An additional current feed line, an additional power supply and an additional superconducting switch are required for this purpose.

(32) The LTS coil section which can be charged independently can then be chosen such that the coupling with the HTS coil is optimal. It is also possible to design this LTS coil section with a notch and thereby determine the homogeneity of the magnetic field B0 in the test volume at the end of the charging process.

(33) In particular, the LTS shield section (which is usually incorporated to reduce the stray field) is suitable for inductive charging as this couples to the HTS coil with negative coupling inductance.

(34) FIG. 3 shows schematically a corresponding magnet arrangement 1 for a cryostat according to the invention; first and foremost, the differences from the embodiment of FIG. 1 are explained.

(35) Here, the LTS portion 2 comprises the outer LTS shield section (shield coil) 3 as a first LTS section 11, and the inner LTS main section (main coil) 4 as a second LTS section 12; both are connected electrically in series. The first LTS section 11 can be charged via the external current feed lines T1, T2 with the power supply 9, and can be superconductingly short-circuited with the superconducting switch 14a. The second LTS section 12 can be charged via the external current feed lines T2 and T3 with a power supply 13 and can be superconductingly short-circuited by means of a superconducting switch 14b. Here, the HTS portion (HTS coil) 5 is, in turn, designed with a single HTS section 6.

(36) Charging then takes place by way of example in accordance with the following scheme: The background magnet 2 (consisting of main coil 4 and shield coil 3) is cooled while the HTS coil 5 is still held above T.sub.c,HTS. Only the main coil 4 of the background magnet 2 is charged and is held at constant current for the rest of the charging process with the power supply 13. In this step, the other power supply 9 keeps the LTS shield section 3 free from current. The shield coil 3 is charged in the wrong direction, i.e. the stray field increases additionally and the magnetic field B0 in the bore increases slightly (without the field-reducing effect of the shield coil 3, the main coil 4 is overloaded; here, however, the above argument relating to the operating current applies). The temperature THTS of the HTS coil 5 is now reduced until it is superconducting. The LTS shield section 3 is now discharged once more and then charged in the right direction. In doing so, the stray field shrinks to its desired value. As a result of the negative coupling coefficient, the current in the HTS coil 5 also increases during this change of current in the LTS shield section 3. During this process, the power supply 13 maintains the main coil 4 at constant current and the magnetic field B0 in the bore increases further. All superconducting switches 14a, 14b are now closed (persistent mode).

(37) In FIG. 4 the characteristic with respect to time of the current I.sub.LTS.sub.1 in the first LTS section 11, of the current I.sub.LTS.sub.2 in the second LTS section 12, the temperature THTS of the HTS coil 5, the temperature T.sub.LTS of the LTS coil 2 and the characteristic with respect to time of the magnetic field B0 in the bore are in each case plotted upwards against time to the right.

(38) In a first phase between t0 and t1 the current I.sub.LTS.sub.2 in the second LTS section 12, that is to say the main coil 4, is brought from zero to a second operating current I.sub.B.sub.2 with the power supply 13 at the charging connections T2, T3. In doing so, the magnetic field B0 already increases. The current I.sub.LTS.sub.1 in the first LTS section 11 is held at zero with the power supply 9. In the meantime, the temperature T.sub.LTS of the LTS portion 2 is already below the (lowest) critical temperature T.sub.c,LTS (with NbTi approx. 10 K, with Nb.sub.3Sn approx. 15 K), here at 4.2 K. The temperature T.sub.HTS of the HTS portion 5 still lies above the transition temperature T.sub.c,HTS (with YBCO approximately 92 K), here approximately 100 K.

(39) In a second phase between t1 and t2, the current I.sub.LTS.sub.1 in the first LTS section 11 is now brought from zero to the interim current I.sub.IN with the power supply 9. Here, this is negative, that is to say has an opposite sign from I.sub.B.sub.1 and I.sub.B.sub.2. The current I.sub.LTS.sub.2 is held at I.sub.B.sub.2 with the power supply 13. In doing so, the magnetic field B0 increases slightly, as the negative I.sub.LTS.sub.1 in the shield coil 3 acts positively on the magnetic field B0.

(40) Between t2 and t3 the temperature T.sub.HTS of the HTS portion 5 is then reduced below its transition temperature T.sub.c,HTS, here likewise to approximately 4.2 K. At the same time, the currents I.sub.LTS.sub.1 and I.sub.LTS.sub.2 are maintained constant with the power supplies 9, 13.

(41) Finally, between t3 and t4, the current I.sub.LTS.sub.1 in the first LTS section 11, that is to say the LTS shield section 3, is changed from I.sub.IN to the positive first operating current I.sub.B.sub.1 by the power supply 9; in doing so, the sign (current flow direction) of the current I.sub.LTS.sub.1 is reversed. The magnet arrangement 1 or the power supply 9 is therefore designed to charge the LTS shield section 3 optionally with or in opposition to the LTS main section 4. In the variant shown I.sub.B.sub.1 is equal to I.sub.B.sub.2. The previous magnetic flux of the shield coil 3 is transferred to the radially smaller HTS coil 5, as a result of which the field strength B0 in the test volume 7 increases; at the same time, with the finally positive current I.sub.LTS.sub.1 in the shield coil 3, the now negative field contribution is overcompensated.

(42) The superconducting switches 14a, 14b can then be closed and the power supplies 9, 13 can be switched off and/or removed.

(43) Independent Temperature Control of the HTS Coil

(44) Different possibilities exist for the independent temperature control of the HTS coil (at least when charging). In general and in particular, with all the embodiments presented in the following, it is advantageous to attach a heater to the HTS coil (or in the tank in which the HTS coil is arranged) in order to be able to raise the temperature of the HTS coil quickly or to hold it at a higher temperature level with respect to the environment.

(45) As shown in FIG. 5 with reference to a schematic section through a cryostat 20 according to the invention, the HTS coil 5 can be accommodated in a separate, second helium tank 22 which is independent of a first helium tank 21 in which the LTS coil 2 is arranged.

(46) In the embodiment shown, the LTS coil (the LTS portion) 2 comprises an LTS shield section 3 made from NbTi wire and an LTS main section 4 with three sub-coil sections 23a, 23b, 23c, of which the outermost is made from NbTi wire and the two inner 23b, 23c from Nb.sub.3Sn wire. Here, both helium tanks 21, 22 are in each case designed with a neck tube for filling with helium and, in the case of the first tank 21, also for the external current feed lines (not shown in more detail). The second helium tank 22 is provided with an electrical heater 29. In the state of normal operation shown, both helium tanks 21, 22 are filled with liquid helium at 4.2 K; it is to be noted that, during charging, the second helium tank 22 and the HTS coil 5 respectively must be temporarily brought to a warm state while the helium thereof is in gaseous form (or is not present) in the second helium tank 22.

(47) Both helium tanks 21, 22 are arranged in a vacuum container 24; here the walls 24a thereof simultaneously form the outer wall of the cryostat 20. Furthermore, a radiation shield 25a, which is cooled by liquid nitrogen (LN.sub.2) in an outer tank 25, is provided; the helium tanks 21, 22 are also located inside this radiation shield 25a. For simplification, a boundary of the radiation shield 25a with the room temperature bore 26 is not shown in more detail here.

(48) In the embodiment of FIG. 5 shown, the helium tanks 21, 22 are arranged closely next to one another (without a radiation shield) in order to fill the space near the room temperature bore 26 to a maximum with coils.

(49) In an alternative embodiment, which is shown in FIG. 6 and corresponds substantially to the embodiment of FIG. 5, an additional radiation shield 27 is arranged between the helium tanks 21, 22 in the vacuum container 24. In the simplest case (and preferred), this is not thermally coupled to the walls of the radiation shield 25a (and also not otherwise thermally coupled to the structures of the cryostat 20); in this case, a mean temperature between first and second helium tank 21, 22 is established on the radiation shield 27 and, due to radiation reflection, the heat introduced in the colder helium tank (the first helium tank 21 when charging) is approximately halved compared with the case without radiation shield 27. Alternatively, the radiation shield 27 is thermally coupled to the radiation shield 25a by means of suitable metallic connections and accordingly is at the temperature of the liquid nitrogen in the outer tank 25 at approx. 77 K.

(50) Furthermore, as shown in FIG. 7, with a cryostat 20 similar to that shown in FIG. 5, the HTS coil 5 can also be arranged in a second helium tank 22 which can be connected by means of a valve 28 to the first helium tank 21 in which the LTS coil 5 is arranged. This enables the second helium tank 22 to be filled with liquid helium from the first helium tank 21 (overflow valve). It is advantageous in this case to provide the second helium tank 22 of the HTS coil 5 with a line via which helium can be pumped out (not shown in more detail). In this case, the second helium tank 22 does not require a neck tube, as shown in FIG. 7.

(51) In an embodiment of a cryostat 20 of FIG. 8, which is similar to the embodiment of FIG. 5, the HTS coil 5 is arranged in the vacuum chamber 24b of the vacuum container 24. The HTS coil 5 can be coupled to the helium tank 21 of the LTS portion 2 or disconnected from the helium tank 21 by means of a heat switch 30 (heat switch), e.g., a gas gap heat switch.

(52) HTS Coils

(53) Preferably, HTS materialespecially YBCOis deposited in an annular form on cylindrical substrate material (support body) by means of thin film deposition to produce an HTS coil or HTS section. Hastelloy is preferably used as the substrate material. With the help of laser structuring, an initially continuous, deposited HTS cylindrical sleeve can be divided into a plurality of coaxial adjacent rings. The fabrication of coils (actually a collection of rings) can also be carried out in several layers (i.e., a plurality of coaxial rings or ring layers with increasing radii are produced). At the same time, SrTiO.sub.3 is preferably used as an insulator radially between the rings or ring layers.

(54) A coil produced in this manner can also be used for constructing a high-field NMR magnet. As the HTS rings are continuous, there is no need to produce superconducting connections between HTS conductors. The HTS rings can be formed geometrically such that they are sufficiently thin to not negatively affect the homogeneity of the magnetic field (equivalent to filamentation in NbTi or Nb.sub.3Sn wires).

(55) An HTS coil manufactured as described above is not connected electrically in series with the background magnet (consisting of main and shield coil) made from LTS; there is therefore no need to produce superconducting HTS-LTS connections. Likewise, there is no need to bring out an HTS tape conductor in a complicated manner from the region of the highest magnetic field.

(56) FIG. 9 shows an HTS section 6 for the invention, wherein a total of five closed cylindrical sleeves 38 made from HTS material, here YBCO, are deposited radially on top of one another on a cylindrical support body 31. The HTS section 6 therefore has HTS material in five radial layers 41. An electrical insulation layer 39, here made of strontium titanate (SrTiO.sub.3), is deposited in each case between the cylindrical sleeves 38 and also externally on the outermost cylindrical sleeve 38. The support body 31 has a circular cross section and here is provided on the face ends with end disks 40 which project radially over the cylindrical sleeves 38 and the insulation layers 39.

(57) A further HTS section 6 for the invention, similar to the HTS section of FIG. 9, is shown in FIG. 10. Here, five radial layers 41, each having a multiplicity (here twenty-five) of superconducting rings 32 which are closed in themselves, are arranged on the cylindrical support body 31. An insulation layer 39, here strontium titanate, is in each case arranged between the radial layers 41 and also on the outermost layer 41. The insulation material is likewise arranged axially between the rings 32 of a respective layer 41.

(58) Alternatively, HTS coils or HTS sections can also be produced based on HTS tape conductors. The HTS tape conductor typically comprises a tape-like, metallic substrate (e.g. a sheet steel tape), on which one or more buffer layers (e.g. made from MgO), an HTS layer (e.g. made from YBCO) and, if necessary, shunt and/or protective layers (usually made of Cu or noble metals such as Ag, Au) are deposited.

(59) FIG. 11 shows an HTS section 6 for the invention which is wound with a tape conductor 37 on a cylindrical support body (coil body) 31 in the form of a solenoid. Here, a plurality of layers is wound continuously with the tape conductor 37. The innermost layer and the outermost layer are connected to one another by means of an HTS-HTS joint 36 at a coil end (in FIG. 11, the top end), so that the HTS section 6 is superconductingly short-circuited overall. End disks 40, which project radially over the wound tape conductor 37, are provided at the face ends of the support body 31 (however, in FIG. 11, the top end disk is not shown for better clarity).

(60) FIG. 12 shows an HTS section 6 for the invention in which, with the exception of its two ends 35, a slotted HTS tape conductor 37 has been used. An inner layer 33 of the HTS section 6 has been wound in the form of a solenoid with one half (half tape) of the tape conductor 37 and an outer layer 34 has been wound with the other half of the tape conductor 37; in other embodiments, further coil layers can also be wound with the half tapes. The half tapes connect at the ends 35 without the need for a joint. Methods for winding such an HTS section or HTS coil are described for example in DE 10 2011 082 652 A1.

LIST OF REFERENCES

(61) 1 Magnet arrangement 2 LTS portion (background magnet, LTS coil) 3 LTS shield section (shield coil) 4 LTS main section (main coil) 5 HTS portion (HTS coil) 6 HTS section 7 Test volume 8 Superconducting switch (main switch) 9 Power supply 11 First LTS section 12 Second LTS section 13 Power supply 14a, 14b Superconducting switches 20 Cryostat 21 First helium tank 22 Second helium tank 23a-23c Sub-coil sections 24 Vacuum tank (vacuum container) 24a Wall of vacuum tank 24b Vacuum chamber 25 Outer tank for liquid nitrogen (LN.sub.2) 25a Radiation shield of outer tank for liquid nitrogen 26 Room temperature bore 27 Radiation shield between helium tanks 28 Valve 29 Electrical heater 30 Heat switch 31 Cylindrical support body (coil support) 32 Ring made from HTS material 33 Inner layer 34 Outer layer 35 End of slotted HTS tape conductor 36 HTS-HTS joint 37 HTS tape conductor 38 HTS cylindrical sleeve 39 Insulation layer 40 End disk 41 Radial layer

(62) B0 Magnetic field in the test volume in the direction of the coil axis I.sub.B.sub.1 First operating current I.sub.B.sub.2 Second operating current I.sub.IN Interim current I.sub.LTS.sub.1 Current in the at least one first LTS section I.sub.LTS.sub.2 Current in the at least one second LTS section SA Coil axis t0-t4 Times T1, T2, T3 Current feed lines (charging connections) T.sub.HTS Temperature of HTS portion T.sub.c,HTS Transition temperature of HTS portion T.sub.LTS Temperature of LTS portion T.sub.c,LTS Transition temperature of LTS portion