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Superconducting permanent magnet from Nb3Sn with iron core
THE REDUCTION OF THE PENUMBRA IN THE PREPARATION OF THIN SUPERCONDUCTING FILMS I. A. A R T E M E N K O and I. D. VO1TOVICH Cybernetics Institute, Academy of Sciences, Ukrainian S.S.Ro Received 15 August 1965t
I N preparing thin film cryogenic computer elements by vacuum deposition, the most serious problem is the reduction of the slope of the edges of the film arising from the existence of penumbra from the stencil. We have used an electromagnet by which the stencils are attracted to the substrate to ensure that they lie fiat. The device is shown schematically in Figure 1. The construction provides also for the cooling of the substrate with liquid nitrogen or flowing water. If necessary the substrate can be heated by the warming of the magnet itself. The base of the vessel is made of 3 mm thick nonmagnetic material. Allowing for the thickness of the substrate, the distance between the stencil and the magnet is 3.5 mm. The stencils are made of permalloy or khO-5 steel, of thickness 20-50 Ix. The core of the electromagnet 3 is made of magnetically soft iron, which is galvanized to prevent corrosion. The windings are connected so that when a current is passed through them the bars of the core become magnetized in alternate fields. It was established experimentally that the width of the bars can be chosen equal to the distance from the magnet to the stencil. If two magnets have the same attractive force at distances dl and d2 and the distance between the bars of the magnets are respectively al and a2 then the relation dl/d2 = affa2 is satisfied. On the basis of this relation, the distance between the rods can be chosen for a given distance from magnet to stencil.
The main fear in using the device described was that the stencil attracted to the substrate would destroy the previously deposited layers; however, no breaking of the layers was observed.
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1. Vacuum chamber
4. Evaporator
2. Vessel
5. Substrata 6, Stencil
3. Electromagnet
t Received by PTI~ Editor 24 January 1964: Pribory i Tekhnika Eksperimenta, No. 1,224 (1965)
Figure 1. Device for attracting the stencil to the substrata
SUPERCONDUCTING PERMANENT MAGNET FROM Nb3Sn WITH IRON CORE F. L A N G E Institiit fiir Tieftemperaturphysik der Deutschen Akademie der Wissenschaften, Forschungsgemeinschaft, Dresden, Germany Received 18 November 1965
investigations in superconducting niobiumzirconium wires required a magnetic field with a field strength of 50-60 kOe, which would not vary with OUR
108
time, and which was concentrated in a very narrow space. The stray field should be as low as possible. T o meet these demands, a NbaSn hollow cylinder CRY()GENICS • APRIL 1966
described in a previous paper by this author I was provided with an additional iron core (Figure 1). To maintain accessibility of the measuring space the hollow cylinder had two 0.6 mm bores through which, for example, a niobium-zirconium wire could be passed. The bores caused a reduction of 3 kOe in
1! Figure 1. Arrangement of the permanent magnet
the field which remained trapped in the hollow cylinder, without iron core, at 4.2 ° K; it dropped from 25 to 22 kOe. From the results of our investigations, no variation could be detected with respect to the behaviour of the superconducting hollow cylinder whether measured without core, with pole pieces alone, or with pole pieces and outer iron jacket. This is especially valid for the tendency to flux jumps. The iron magnetic circuit was made of an ironcobalt alloy containing 35 per cent cobalt and thoroughly forged. The expected additional fields
could be obtained. With cylindrical pole plugs and a gap of 0.5 mm we attained a total field of 46 kOe at 4.2 ° K. Omitting the outer iron jacket caused decrease of the field within the gap by less than 1 kOe so that it serves chiefly for reduction of stray field. For further increase of the field, conical pole tips (angle 55 degrees) are used. Within the field space of 1 mm diameter and 0.2 mm height a field of 57 kOe was obtained which was measured with a bismuth magnetoresistance probe, z The permanent magnet has a mass of only 38 g, including the iron core. For energization it requires a field which increases to about 25 kOe within about 1 s and which decreases steadily to zero within about 20 s. In order to avoid flux jumps, the magnet must be immersed in helium-II during energization, and then it may be heated to 4.2 ° K within about 5 min; 1 switching on of heating is necessary already in the helium-II range to avoid release of a flux jump. In the liquid hydrogen range, e.g. at 14 ° K, such digression is not necessary. The Nb3Sn hollow cylinder gives a field of about 7 kOe at this temperature, the additional field of the magnetic circuit being about the same as at helium temperatures. The energizing field is produced by a copper solenoid cooled with liquid nitrogen. 3 This note is part of a paper delivered to the International Conference 'Physics and Techniques of Low Temperatures' in September 1965 in Dresden. I am very grateful to Prof. Dr. Bewilogua fi~r his interest in this work. REFERENCES 1. LANGE, F. Cryogenics5, 143 (1965) 2. DETTMANN, F., and LANGE, F. Exp. tech. Phys. 13, 26 (1965) 3. BARTUSCH, P., HANSEL, G., and LANGE, F. Exp. tech. Phys. 13, 61 (1965)
A CRYOSTAT FOR INTERMEDIATE TEMPERATURESt H. L. L A Q U E R and D. L. DECKER~ University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico, U.S.A. Received 15 October 1965
A c R Y o s T A T with limited convection and requiring no internal vacuum enclosures has been developed for experimental work in the region above the boiling t The work described in this note was performed under the
auspices of the U.S. Atomic Energy Commission. :~Permanent address: Department of Physics, Brigham Young University, Provo, Utah, U.S.A. CRYOGENICS • APRIL 1966
point of helium. Our apparatus appears somewhat similar to that described by Rose-Innes I in that a heated capsule is in limited thermal contact with a liquid helium container, with the contact being provided by conduction and convection in a gas space and by some conduction through metallic linkages. However, since our capsule is located below the liquid 109
I N preparing thin film cryogenic computer elements by vacuum deposition, the most serious problem is the reduction of the slope of the edges of the film arising from the existence of penumbra from the stencil. We have used an electromagnet by which the stencils are attracted to the substrate to ensure that they lie fiat. The device is shown schematically in Figure 1. The construction provides also for the cooling of the substrate with liquid nitrogen or flowing water. If necessary the substrate can be heated by the warming of the magnet itself. The base of the vessel is made of 3 mm thick nonmagnetic material. Allowing for the thickness of the substrate, the distance between the stencil and the magnet is 3.5 mm. The stencils are made of permalloy or khO-5 steel, of thickness 20-50 Ix. The core of the electromagnet 3 is made of magnetically soft iron, which is galvanized to prevent corrosion. The windings are connected so that when a current is passed through them the bars of the core become magnetized in alternate fields. It was established experimentally that the width of the bars can be chosen equal to the distance from the magnet to the stencil. If two magnets have the same attractive force at distances dl and d2 and the distance between the bars of the magnets are respectively al and a2 then the relation dl/d2 = affa2 is satisfied. On the basis of this relation, the distance between the rods can be chosen for a given distance from magnet to stencil.
The main fear in using the device described was that the stencil attracted to the substrate would destroy the previously deposited layers; however, no breaking of the layers was observed.
V////7// i/////////////////1///~
1. Vacuum chamber
4. Evaporator
2. Vessel
5. Substrata 6, Stencil
3. Electromagnet
t Received by PTI~ Editor 24 January 1964: Pribory i Tekhnika Eksperimenta, No. 1,224 (1965)
Figure 1. Device for attracting the stencil to the substrata
SUPERCONDUCTING PERMANENT MAGNET FROM Nb3Sn WITH IRON CORE F. L A N G E Institiit fiir Tieftemperaturphysik der Deutschen Akademie der Wissenschaften, Forschungsgemeinschaft, Dresden, Germany Received 18 November 1965
investigations in superconducting niobiumzirconium wires required a magnetic field with a field strength of 50-60 kOe, which would not vary with OUR
108
time, and which was concentrated in a very narrow space. The stray field should be as low as possible. T o meet these demands, a NbaSn hollow cylinder CRY()GENICS • APRIL 1966
described in a previous paper by this author I was provided with an additional iron core (Figure 1). To maintain accessibility of the measuring space the hollow cylinder had two 0.6 mm bores through which, for example, a niobium-zirconium wire could be passed. The bores caused a reduction of 3 kOe in
1! Figure 1. Arrangement of the permanent magnet
the field which remained trapped in the hollow cylinder, without iron core, at 4.2 ° K; it dropped from 25 to 22 kOe. From the results of our investigations, no variation could be detected with respect to the behaviour of the superconducting hollow cylinder whether measured without core, with pole pieces alone, or with pole pieces and outer iron jacket. This is especially valid for the tendency to flux jumps. The iron magnetic circuit was made of an ironcobalt alloy containing 35 per cent cobalt and thoroughly forged. The expected additional fields
could be obtained. With cylindrical pole plugs and a gap of 0.5 mm we attained a total field of 46 kOe at 4.2 ° K. Omitting the outer iron jacket caused decrease of the field within the gap by less than 1 kOe so that it serves chiefly for reduction of stray field. For further increase of the field, conical pole tips (angle 55 degrees) are used. Within the field space of 1 mm diameter and 0.2 mm height a field of 57 kOe was obtained which was measured with a bismuth magnetoresistance probe, z The permanent magnet has a mass of only 38 g, including the iron core. For energization it requires a field which increases to about 25 kOe within about 1 s and which decreases steadily to zero within about 20 s. In order to avoid flux jumps, the magnet must be immersed in helium-II during energization, and then it may be heated to 4.2 ° K within about 5 min; 1 switching on of heating is necessary already in the helium-II range to avoid release of a flux jump. In the liquid hydrogen range, e.g. at 14 ° K, such digression is not necessary. The Nb3Sn hollow cylinder gives a field of about 7 kOe at this temperature, the additional field of the magnetic circuit being about the same as at helium temperatures. The energizing field is produced by a copper solenoid cooled with liquid nitrogen. 3 This note is part of a paper delivered to the International Conference 'Physics and Techniques of Low Temperatures' in September 1965 in Dresden. I am very grateful to Prof. Dr. Bewilogua fi~r his interest in this work. REFERENCES 1. LANGE, F. Cryogenics5, 143 (1965) 2. DETTMANN, F., and LANGE, F. Exp. tech. Phys. 13, 26 (1965) 3. BARTUSCH, P., HANSEL, G., and LANGE, F. Exp. tech. Phys. 13, 61 (1965)
A CRYOSTAT FOR INTERMEDIATE TEMPERATURESt H. L. L A Q U E R and D. L. DECKER~ University of California, Los Alamos Scientific Laboratory, Los Alamos, New Mexico, U.S.A. Received 15 October 1965
A c R Y o s T A T with limited convection and requiring no internal vacuum enclosures has been developed for experimental work in the region above the boiling t The work described in this note was performed under the
auspices of the U.S. Atomic Energy Commission. :~Permanent address: Department of Physics, Brigham Young University, Provo, Utah, U.S.A. CRYOGENICS • APRIL 1966
point of helium. Our apparatus appears somewhat similar to that described by Rose-Innes I in that a heated capsule is in limited thermal contact with a liquid helium container, with the contact being provided by conduction and convection in a gas space and by some conduction through metallic linkages. However, since our capsule is located below the liquid 109