Present situation of temperature measurement by means of platinum resistance thermometers below 0°C is described. After a short note on available equipment, the method of representating the relationship between the resistance and thermodynamic temperature is dealt with. Above the triple point of hydrogen, the extension of the International Practical Temperature Scale below 90°K and its improvement above 90°K are referred to, and a method of obtaining the temperature from a reference table such as CCT-64 and calibration at several thermometric fixed points, which has been proposed at the Comité Consultatif de Thermométrie, is described. Below the triple point of hydrogen down to helium temperatures, the resistance-temperature relationship of platinum is discussed.
Pulse Tube Refrigeration is a new refrigeration method which was conceived by W. E. Gifford in 1961. This refrigerator can make a low temperature without any mechanical devices, actually, a temperature of 26°K has already been achieved with a LN2 cooling single stage refrigerator and a 43°K with 4 stage refrigerator. The interest in the method is due to the fact that, though the phenomenon is very complex and difficult to analyze, the equipment of a Pulse Tube Refrigerator can be very small and simple. The notes that have been assembled here try to give a basic understanding of the surface heat pumping mechanism, its characteristics, advantages and limitations. These should provide enough information for making a decision regarding the development of Pulse Tube Refrigerator.
A new method for measuring contact resistance of composite conductors is proposed and some results measured are described of contact resistance and resistance ratio (300°K/4.2°K) of various stabilized superconducting wires. By the method that we formerly proposed, the longitudinal potential variation of conductor with current electrodes suitably attached can be measured by a voltage-probe or terminals, and then contact resistance may be computed from the characteristic value of attenuation. Our stabilized superconducting wires, copper electro-plated wires (NbZr or NbTi) and mechanically bonded wires (NbTi), have a contact resistance of about 0.05μΩ-cm2 which is considerably lower than those of commercially available wires. As for resistance ratio, mechanically bonded wires with O. F. H. C. copper are naturally better than electro-plated wires. The former has resistance ratios of 150-250, while the latter has ratios of 30-100. The formation of a intermetallic compound was sharply detected by this method. A jump in contact resistance was found near the transition temperature of superconductor.
The equipment producing a cusp type magnetic field, which is used to trap high temperature plasma, by a pair of superconducting magnets, was constructed. The working space of a cusp field is 20mm between the two magnets and 10mm in the inner diameter of each magnet. The rated magnetic field at the center of each coil is 40kG. The maximum tested field is 55kG. Each superconducting coil is sealed in a liquid helium vessel, to which liquid helium is supplied from a liquid helium supplying vessel. The capacity of the liquid helium supplying vessel is about 5l, and the average helium loss is about 1.8l/h at 40kG of the field strength.