Heat switch

A special care is to be devoted to the control that all the parts of the apparatus have reached the desired temperature when parts remain at higher temperature, due to the high value of the specific heat, the cooling only by radiative exchange is usually impossible. To open a gas heat switch, several hours of pumping are usually necessary to reduce the pressure to a value suitable for the thermal isolation. An insufficient pumping leads to a time-dependent heat leak due to desorption and condensation of the residual gas at the coldest surfaces. 

Small-size fixed magnets with fields up to 1T are nowadays commercially available they usually retain their characteristics at low temperature. Variable field magnets are used to operate superconducting heat switches or for NMR thermometers. 

In the last decades, aluminium and aluminium alloys have received an increasing interest in cryogenic applications [5-7], Pure aluminium is used in the building of superconducting heat switches (see Section 4.3) because of its high switching ratio [8,9] and convenient critical field. Satisfactory procedures for welding have also been found [10,11],... 

The key point of our transistor model is the negative differential heat resistance as we observed in the diode model(Li Wang Casati, 2004). It provides the possibility that when Ta changes both Js and Jd change simultaneously in the same way. Therefore Js = Jd (or Js Jd) can be achieved for several different values of T0 or even in a wide region of T0 as shown in Figs.10 and 11. In this situation heat switch and heat modulator/amplifier are possible. In the ideal, limiting... 

Mode of operation Starting from atmospheric pressure with the process heating switched off, valve V1 is initially open (maximum switching point exceeded) so that atmospheric pressure also prevails in the reference chamber. 

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