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Quick coupling connector adapted for use at low temperatures
Quick coupling connector adapted for use at low temperatures J. C. H O M O and P. L E V I N S O N
T H I S C O N N E C T O R was designed to allow easy handling of connexions at low temperatures (liquid or even superfluid helium). Basically, it is designed like a classical vacuum connector, but the usual O-ring has been replaced by a disposable teflon gasket, and the connecting parts have been modified so that in order to increase pressure, the compressed surface of the gasket is very small (see Figure 1). Thus in the case of a 9 mm i d connector, where the pressed area is no more than 30 mm z, teflon film 0.1 mm thick is used. Inside the connector it is compressed beyond its elastic limit so that the pressed area becomes transparent. When leak testing on a helium mass spectrometer, it must be kept in mind that helium diffuses through teflon at room t e m p e r a t u r e (for example, diffusion was measured at 5 x 10-8 x 1/s from a 9 mm i d connector). Therefore, when testing the other parts of the connector for leaks, helium is kept away from the gasket area by adhesive tape. The gasket itself is tested by wrapping the connector in a plastic bag filled with helium gas, and immersing into liquid nitrogen. The teflon then becomes gas tight at low temperatures, helium stops diffusing into the connector, and the drop in diffusion can be detected with the helium leak detector.
The clamping ring is made of brass; friction and expansion coefficients of which best match those of the stainless steel used for the connector. I
The authors are with the Laboratoire de Physique Theorique, College de France, 11 Place Marcelin, Berthelot, Paris (5e), France. Received 18 April 1969.
1. LEVINSON,P., LABERRIGUE,A., and TESTARD,O. Cryogenics S, 345 (1965)
Convenient method for applying force to a mechanical heat switch, for use in low temperature specific heat measurements D. H. L O W N D E S and L. FINEGOLD
I N L O W temperature heat capacity measurements, it has long been a standard practice to use a mechanical heat switch to establish thermal contact between a sample (situ in vacua) and its surroundings (often a liquid helium bath). Both the reasons for using a mechanical switch i The authors are with the Department of Physics and Astrophysics, University of Colorado, Boulder, Colorado, USA. LF is at present with the Department of Physics, University of Sussex, Falmer, Brighton, Sussex, UK. Received 21 April 1969. .382
A brass clamping ring C tube, i d g m m E brass screw
B D
connector, o d 15 mm details of gasket, compressed area 1 mm ct angle of the connector, 30 deg
Figure 1. Scheme of connector
REFERENCE
(rather than some other method of making thermal contact), and the considerations determining the optimum design of a heat switch, 2 have been considered in several thorough and nearly exhaustive papers on the subject. Nevertheless, one still encounters a succession of several purely practical problems in constructing a heat switch which is completely reliable and at the same time both simple to assemble and convenient to operate. The thermal conductance of a pair of pressed contacts varies nearly linearly with the pressure, and thus is independent of the contact area for a given total load. a This fact combined (usually) with the need to conserve space in the sample chamber, has led to the design of relatively small area contacts, requiring the application of much force for efficient heat transfer. Typically, the force is generated outside of the cryostat (at room temperature) and transmitted to the sample chamber by means of stainless steel tubes or rods. However, the assembly of a switch operating mechanism utilizing tubes can become rather complicated and some care is required to avoid binding and vibration (which heats the sample) when the switch is operated. In CRYOGENICS • OCTOBER 1969
T H I S C O N N E C T O R was designed to allow easy handling of connexions at low temperatures (liquid or even superfluid helium). Basically, it is designed like a classical vacuum connector, but the usual O-ring has been replaced by a disposable teflon gasket, and the connecting parts have been modified so that in order to increase pressure, the compressed surface of the gasket is very small (see Figure 1). Thus in the case of a 9 mm i d connector, where the pressed area is no more than 30 mm z, teflon film 0.1 mm thick is used. Inside the connector it is compressed beyond its elastic limit so that the pressed area becomes transparent. When leak testing on a helium mass spectrometer, it must be kept in mind that helium diffuses through teflon at room t e m p e r a t u r e (for example, diffusion was measured at 5 x 10-8 x 1/s from a 9 mm i d connector). Therefore, when testing the other parts of the connector for leaks, helium is kept away from the gasket area by adhesive tape. The gasket itself is tested by wrapping the connector in a plastic bag filled with helium gas, and immersing into liquid nitrogen. The teflon then becomes gas tight at low temperatures, helium stops diffusing into the connector, and the drop in diffusion can be detected with the helium leak detector.
The clamping ring is made of brass; friction and expansion coefficients of which best match those of the stainless steel used for the connector. I
The authors are with the Laboratoire de Physique Theorique, College de France, 11 Place Marcelin, Berthelot, Paris (5e), France. Received 18 April 1969.
1. LEVINSON,P., LABERRIGUE,A., and TESTARD,O. Cryogenics S, 345 (1965)
Convenient method for applying force to a mechanical heat switch, for use in low temperature specific heat measurements D. H. L O W N D E S and L. FINEGOLD
I N L O W temperature heat capacity measurements, it has long been a standard practice to use a mechanical heat switch to establish thermal contact between a sample (situ in vacua) and its surroundings (often a liquid helium bath). Both the reasons for using a mechanical switch i The authors are with the Department of Physics and Astrophysics, University of Colorado, Boulder, Colorado, USA. LF is at present with the Department of Physics, University of Sussex, Falmer, Brighton, Sussex, UK. Received 21 April 1969. .382
A brass clamping ring C tube, i d g m m E brass screw
B D
connector, o d 15 mm details of gasket, compressed area 1 mm ct angle of the connector, 30 deg
Figure 1. Scheme of connector
REFERENCE
(rather than some other method of making thermal contact), and the considerations determining the optimum design of a heat switch, 2 have been considered in several thorough and nearly exhaustive papers on the subject. Nevertheless, one still encounters a succession of several purely practical problems in constructing a heat switch which is completely reliable and at the same time both simple to assemble and convenient to operate. The thermal conductance of a pair of pressed contacts varies nearly linearly with the pressure, and thus is independent of the contact area for a given total load. a This fact combined (usually) with the need to conserve space in the sample chamber, has led to the design of relatively small area contacts, requiring the application of much force for efficient heat transfer. Typically, the force is generated outside of the cryostat (at room temperature) and transmitted to the sample chamber by means of stainless steel tubes or rods. However, the assembly of a switch operating mechanism utilizing tubes can become rather complicated and some care is required to avoid binding and vibration (which heats the sample) when the switch is operated. In CRYOGENICS • OCTOBER 1969