- Email: [email protected]
A simple helium-3 cryostat
A SIMPLE HELIUM-3 CRYOSTAT B. N. ESEL'SON, B. G. LAZAREV, and A. D. SHVETS Physico-Technical Institute, Academy of Sciences, Ukrainian S.S.R. Received 16 April 1963 t
H E L I U M- 3 crystals are now being used even more extensively to obtain temperatures below 1° K. 1-6 As would be expected, such apparatus, with which temperatures down to 0.3 ° K can be reached, are complicated. In all the helium-3 cryostats in existence the reduction in temperature is achieved by pumping the vapour either with a diffusion pump or a rotary pump, or by the two together. When working with such a rare substance as helium-3 it is natural to aim 1~) c m
-A s-__
t,-
i.~
13
"Figure 1
•['Received by PTI~ Editor 29 November 1961: Pribory i Tekhnika l~ksperimenta No. 3, p. 198 (1962). CRYOGENICS
• DECEMBER
1963
for maximum simplification in the arrangement and reliability in its operation. By applying a charcoal adsorption pump for p u m p ing the vapour, as used earlier in helium-4 apparatus, 7 by dispensing with vacuum a n d forevacuum pumps we were able to avoid many difficulties and to produce the simple arrangement shown in Figure I, with which temperatures down to 0.34 ° K can be reached. This apparatus consists of the charcoal adsorption pump 1, the liquid helium-3 reservoir 3, and the cylinders 4 and 10 for storing the gaseous helium-3. The charcoal pump 1 can be disconnected from reservoir 3 during condensation of the helium-3 by valve 6, which also controls the pumping speed for the vapour, i.e. the temperature reached. The adsorption pump consists of a brass cylinder, 50 mm in diameter and 160 mm high, inside which 30 g of activated charcoal is contained between two brass gauzes (see the section through AA in Figure 1). Reservoir 3, inside which is a copper spiral to even out the temperature within the liquid helium-3 volume, is connected to the charcoal pump by the 4 mm diameter, 120 mm long, thin walled stainless steel tube 2, and is placed inside a glass vacuum jacket 5. This jacket is filled at room temperature with gaseous helium to a pressure of a few millimetres of mercury, and when the apparatus is cooled this is adsorbed by a small quantity of charcoal (2 g) placed in its upper part. The whole arrangement described is inside Dewar 7, which contains liquid helium cooled to 1.3 ° K b y normal means. At this tempe.rature, gaseous helium from cylinder 4 is condensed into reservoir 3 through tube 11. After condensation is finished, valve 6 is opened and reservoir 3 is connected to the pump 1'. This obviously leads to a lowering of the temperature of the helium-3 Which, under the conditions described, reaches 0-34 ° K. This temperature is attained ~ 30 rain after the start of pumping, and with 2 1. of gaseous helium-3 employed then stays constant 4-5 hr. The heat influx to the system is ~ 600 erg]sec. The construction of the cryostat makes it possible to cool not only the helium-3 reservoir but vessel 8 which surrounds it, filled either with a weak holium-3helium-4 mixture (7-4 per cent h e l i u m - 3 ) o r with pure helium-4. The use of an i~otopic mixture for this 207
purpose has definite advantages compared with pure helium-4, since the heat influx connected with the formation of the helium II film is greatly decreased. The minimum temperature of 0.37 ° K, obtained on cooling a mixture by the helium-3, remained constant for 2.5 hr. The temperature increased to 0.41 ° K on cooling helium-4 and was maintained for an appreciably smaller tirrte. At the end of an experiment after warming up, the helium-3 was collected in cylinder 4 and the amount left over was pumped by the charcoal adsorption pump 10, cooled by liquid hydrogen. A pressure of 0.2 mm Hg then remains in the apparatus. It is possible to dispense with cylinder 4 and to use the charcoal pump 10 as the only store for gaseous helium-3. The temperature was determined from the helium-3 vapour pressure, using a MeLeod gauge, and also by a carbon resistance thermometer. We are grateful to V. G. Ivantsov for assistance in carrying out the experiments.
208
REFERENCES 1. ROBERTS, T. R., a n d SYDORIAK, S. G. Phys. Rev. 98, 1672
(t955) 2. SYDOmAK, S. G., a n d ROBERTS, T. R. Prec. 5th Internat. Conf. Low Temperature Physics, Wisconsin, 1957, p. 212 3. SEIDEL, G., a n d KEESOM, P. H. Rev. sci. lnstrum. 29, 606 (1958) 4. P ~ . K O V , V. P., ZINEV'EVA, K. N., a n d FILIMO~qOV, A. I. J. exp. theor. Phys. 36, 1034 (1959), Soviet Phys. JETP 9, 734 (1959) 5. REICH, H. A., a n d GARWIN, R. L. Rev. sci. lnstrum, 30, 7
(1959) 6. ESEL~SON, B. N., SHVETS, A. D., a n d BEREZNYAK, N. G. Prib. i Tekh. ffgksper. No. 6, p. 123 (1961); Cryogenics 2, 361 (1962) 7. ESEL'SON, B. N., LAZAREV, B. G., a n d S,VETS, A. D. Prib. i Tekh. l~ksper. N o . 5, p. 160 (1961)
This paper has been specially translated for CRYO4~3ENICSand is included by permtss|on of the Editors ofPribory i Tekhnika Eksperimenta. We are also indebted to the Instrument Society of America and the Plenum Press, who publish their own cover-to-cover translation of pTI~ by arrangement with the Russian publisher.
CRYOGENICS
• DECEMBER
1963
H E L I U M- 3 crystals are now being used even more extensively to obtain temperatures below 1° K. 1-6 As would be expected, such apparatus, with which temperatures down to 0.3 ° K can be reached, are complicated. In all the helium-3 cryostats in existence the reduction in temperature is achieved by pumping the vapour either with a diffusion pump or a rotary pump, or by the two together. When working with such a rare substance as helium-3 it is natural to aim 1~) c m
-A s-__
t,-
i.~
13
"Figure 1
•['Received by PTI~ Editor 29 November 1961: Pribory i Tekhnika l~ksperimenta No. 3, p. 198 (1962). CRYOGENICS
• DECEMBER
1963
for maximum simplification in the arrangement and reliability in its operation. By applying a charcoal adsorption pump for p u m p ing the vapour, as used earlier in helium-4 apparatus, 7 by dispensing with vacuum a n d forevacuum pumps we were able to avoid many difficulties and to produce the simple arrangement shown in Figure I, with which temperatures down to 0.34 ° K can be reached. This apparatus consists of the charcoal adsorption pump 1, the liquid helium-3 reservoir 3, and the cylinders 4 and 10 for storing the gaseous helium-3. The charcoal pump 1 can be disconnected from reservoir 3 during condensation of the helium-3 by valve 6, which also controls the pumping speed for the vapour, i.e. the temperature reached. The adsorption pump consists of a brass cylinder, 50 mm in diameter and 160 mm high, inside which 30 g of activated charcoal is contained between two brass gauzes (see the section through AA in Figure 1). Reservoir 3, inside which is a copper spiral to even out the temperature within the liquid helium-3 volume, is connected to the charcoal pump by the 4 mm diameter, 120 mm long, thin walled stainless steel tube 2, and is placed inside a glass vacuum jacket 5. This jacket is filled at room temperature with gaseous helium to a pressure of a few millimetres of mercury, and when the apparatus is cooled this is adsorbed by a small quantity of charcoal (2 g) placed in its upper part. The whole arrangement described is inside Dewar 7, which contains liquid helium cooled to 1.3 ° K b y normal means. At this tempe.rature, gaseous helium from cylinder 4 is condensed into reservoir 3 through tube 11. After condensation is finished, valve 6 is opened and reservoir 3 is connected to the pump 1'. This obviously leads to a lowering of the temperature of the helium-3 Which, under the conditions described, reaches 0-34 ° K. This temperature is attained ~ 30 rain after the start of pumping, and with 2 1. of gaseous helium-3 employed then stays constant 4-5 hr. The heat influx to the system is ~ 600 erg]sec. The construction of the cryostat makes it possible to cool not only the helium-3 reservoir but vessel 8 which surrounds it, filled either with a weak holium-3helium-4 mixture (7-4 per cent h e l i u m - 3 ) o r with pure helium-4. The use of an i~otopic mixture for this 207
purpose has definite advantages compared with pure helium-4, since the heat influx connected with the formation of the helium II film is greatly decreased. The minimum temperature of 0.37 ° K, obtained on cooling a mixture by the helium-3, remained constant for 2.5 hr. The temperature increased to 0.41 ° K on cooling helium-4 and was maintained for an appreciably smaller tirrte. At the end of an experiment after warming up, the helium-3 was collected in cylinder 4 and the amount left over was pumped by the charcoal adsorption pump 10, cooled by liquid hydrogen. A pressure of 0.2 mm Hg then remains in the apparatus. It is possible to dispense with cylinder 4 and to use the charcoal pump 10 as the only store for gaseous helium-3. The temperature was determined from the helium-3 vapour pressure, using a MeLeod gauge, and also by a carbon resistance thermometer. We are grateful to V. G. Ivantsov for assistance in carrying out the experiments.
208
REFERENCES 1. ROBERTS, T. R., a n d SYDORIAK, S. G. Phys. Rev. 98, 1672
(t955) 2. SYDOmAK, S. G., a n d ROBERTS, T. R. Prec. 5th Internat. Conf. Low Temperature Physics, Wisconsin, 1957, p. 212 3. SEIDEL, G., a n d KEESOM, P. H. Rev. sci. lnstrum. 29, 606 (1958) 4. P ~ . K O V , V. P., ZINEV'EVA, K. N., a n d FILIMO~qOV, A. I. J. exp. theor. Phys. 36, 1034 (1959), Soviet Phys. JETP 9, 734 (1959) 5. REICH, H. A., a n d GARWIN, R. L. Rev. sci. lnstrum, 30, 7
(1959) 6. ESEL~SON, B. N., SHVETS, A. D., a n d BEREZNYAK, N. G. Prib. i Tekh. ffgksper. No. 6, p. 123 (1961); Cryogenics 2, 361 (1962) 7. ESEL'SON, B. N., LAZAREV, B. G., a n d S,VETS, A. D. Prib. i Tekh. l~ksper. N o . 5, p. 160 (1961)
This paper has been specially translated for CRYO4~3ENICSand is included by permtss|on of the Editors ofPribory i Tekhnika Eksperimenta. We are also indebted to the Instrument Society of America and the Plenum Press, who publish their own cover-to-cover translation of pTI~ by arrangement with the Russian publisher.
CRYOGENICS
• DECEMBER
1963