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Low temperature sealed electrical leads
Low temperature sealed electrical leads O . P. A n a s h k i n
The neck of the vessel is usually used for leading current and potential leads to the inner space of a helium cryostat. A design for low temperature sealed leads into the helium region of a cryostat directly from the vacuum space has been published. 1 The design of leads which we have developed seems to us simpler and more compact and enables several wires to be led into the helium space together. Fig. 1 is a schematic drawing of the lead. 0.2 mm diameter P E V - 2 wire, 2, is wound spirally on the 3 x 0.5 mm copper tube, 1. The number of wires used reached 20. Tube 1 with the wires was glued into copper tube 3, 6 mm diameter, 1 mm wall thickness, soldered into the wall of the helium container. Tube 1 is electrically insulated from tube 3, that is from the case of the cryostat and from the leads. It can be used either directly as a current lead or this can be soldered to it. We soldered at 1.5 mm diameter superconducting lead, 4, of Nb + Ti alloy to tube 1. The breakdown voltage between different parts o f the structure is not less than 1 kV. We used V T - 2 0 0 adhesive developed at VNII from plastic pastes, for glueing the leads. The adhesive has a working time of 1 hour and polymerization time of 48 hours at room temperature or 4 hours at a temperature of + 90°C. The adhesive is stronger in the latter case. The leads were tested by ten rapid coolings in liquid helium or nitrogen and heating in hot water, while the sealing of
Fig.1
Plan of the lead
the leads was continuously checked with a helium leak detector. The leads remained vacuum tight after the tests. Leads made in this way were used successfully in a working cryostat. Apart from the leads described, we also successfully tested low temperature vacuum leads of plane superconducting strips (with and without additional conductors), of single conductors and others, V T - 2 0 0 adhesive being used in all cases. The authors are very grateful to B. N. Samoilov, N. A. Shmidt and M. V. Pomoshnikova for valuable discussions and help in the work.
References The author is with the Institute of Atomic Energy, Moscow, USSR. Prib i Tekh Eksper No 2 (1972) 2250. Received 25 June 1972.
1 Samoilov, B. N. J T F 22 (1952) 888
An empirical function between the resistance and the temperature of a carbon thermometer for 0.3 to 4.2 K W. S a n o a n d S. I s o t a n i
Carbon resistors are largely used as a thermometer for low temperature measurements because they have high sensitivity, small volume, low variation with magnetic fields, and low cost. However, the temperature dependence of the resistivity of these resistors does not have good reproducibility after cooling to liquid helium temperature. Recalibration of the same thermometer is necessary for each experiment if we are to obtain precise measurements of the temperature. The calibration of a thermometer of this type gives us some pairs of points of the resistance R and the temperature T, thus an interpolation formula is necessary to obtain intermediate points. Several empirical formulas are used due to the popularity of the carbon thermometers. It is our purpose to present a new function for the AllenBradley carbon resistor applicable in the temperature range between 0.3 and 4.2 K. The authors are with the Instituto de Fisica da Universidade de Sao Paulo, Sao Paulo, Brazil. Received 10 July 1972.
CRYOGENICS.
MARCH
1973
The Allen-Bradley resistors of 10 to 500 ~ are the most commonly used 1 in cryogenics work above 1 K. Because they have high resistivity below 1 K, the Speer Carbon Co resistors are prefered in this temperature range. Our specific heat measurements between 0.3 to 4.2 K necessitate the use of a unique resistor for these temperature measurements. Our choice of thermometer to cover this range o f temperatures was a 10 ~2, 0. I W Allen-Bradley resistor, mainly because of its good sensitivity above 1 K, while below 1 K, the resistance is large but is in the range of our resistance bridge. The experimental data of the present work were obtained in our heat capacity measurements. 2 The temperature measurements were made by measuring the vapour pressure of He 3 ( 0 . 3 - 1 . 2 K), by means of an Baratron electronic pressure meter, and He 4 ( 1 . 2 - 4 . 2 K) by means of mercury and oil manometers. These vapour pressures were converted to temperature through the well-known NBS tables of 1962
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The neck of the vessel is usually used for leading current and potential leads to the inner space of a helium cryostat. A design for low temperature sealed leads into the helium region of a cryostat directly from the vacuum space has been published. 1 The design of leads which we have developed seems to us simpler and more compact and enables several wires to be led into the helium space together. Fig. 1 is a schematic drawing of the lead. 0.2 mm diameter P E V - 2 wire, 2, is wound spirally on the 3 x 0.5 mm copper tube, 1. The number of wires used reached 20. Tube 1 with the wires was glued into copper tube 3, 6 mm diameter, 1 mm wall thickness, soldered into the wall of the helium container. Tube 1 is electrically insulated from tube 3, that is from the case of the cryostat and from the leads. It can be used either directly as a current lead or this can be soldered to it. We soldered at 1.5 mm diameter superconducting lead, 4, of Nb + Ti alloy to tube 1. The breakdown voltage between different parts o f the structure is not less than 1 kV. We used V T - 2 0 0 adhesive developed at VNII from plastic pastes, for glueing the leads. The adhesive has a working time of 1 hour and polymerization time of 48 hours at room temperature or 4 hours at a temperature of + 90°C. The adhesive is stronger in the latter case. The leads were tested by ten rapid coolings in liquid helium or nitrogen and heating in hot water, while the sealing of
Fig.1
Plan of the lead
the leads was continuously checked with a helium leak detector. The leads remained vacuum tight after the tests. Leads made in this way were used successfully in a working cryostat. Apart from the leads described, we also successfully tested low temperature vacuum leads of plane superconducting strips (with and without additional conductors), of single conductors and others, V T - 2 0 0 adhesive being used in all cases. The authors are very grateful to B. N. Samoilov, N. A. Shmidt and M. V. Pomoshnikova for valuable discussions and help in the work.
References The author is with the Institute of Atomic Energy, Moscow, USSR. Prib i Tekh Eksper No 2 (1972) 2250. Received 25 June 1972.
1 Samoilov, B. N. J T F 22 (1952) 888
An empirical function between the resistance and the temperature of a carbon thermometer for 0.3 to 4.2 K W. S a n o a n d S. I s o t a n i
Carbon resistors are largely used as a thermometer for low temperature measurements because they have high sensitivity, small volume, low variation with magnetic fields, and low cost. However, the temperature dependence of the resistivity of these resistors does not have good reproducibility after cooling to liquid helium temperature. Recalibration of the same thermometer is necessary for each experiment if we are to obtain precise measurements of the temperature. The calibration of a thermometer of this type gives us some pairs of points of the resistance R and the temperature T, thus an interpolation formula is necessary to obtain intermediate points. Several empirical formulas are used due to the popularity of the carbon thermometers. It is our purpose to present a new function for the AllenBradley carbon resistor applicable in the temperature range between 0.3 and 4.2 K. The authors are with the Instituto de Fisica da Universidade de Sao Paulo, Sao Paulo, Brazil. Received 10 July 1972.
CRYOGENICS.
MARCH
1973
The Allen-Bradley resistors of 10 to 500 ~ are the most commonly used 1 in cryogenics work above 1 K. Because they have high resistivity below 1 K, the Speer Carbon Co resistors are prefered in this temperature range. Our specific heat measurements between 0.3 to 4.2 K necessitate the use of a unique resistor for these temperature measurements. Our choice of thermometer to cover this range o f temperatures was a 10 ~2, 0. I W Allen-Bradley resistor, mainly because of its good sensitivity above 1 K, while below 1 K, the resistance is large but is in the range of our resistance bridge. The experimental data of the present work were obtained in our heat capacity measurements. 2 The temperature measurements were made by measuring the vapour pressure of He 3 ( 0 . 3 - 1 . 2 K), by means of an Baratron electronic pressure meter, and He 4 ( 1 . 2 - 4 . 2 K) by means of mercury and oil manometers. These vapour pressures were converted to temperature through the well-known NBS tables of 1962
179