Thermal-buble initiated breakdown characteristics of liquid helium and nitrogen at atmospheric pressure
Experiments show that electric field promotes to form a vapor locking in a gap with a hot spot and in turn the formation of locked vapor produces the serious reduction of breakdown voltage. Especially it is argued that the dielectric strength of liquid helium under serious hot spot conditions decreases below that for saturated gas.
Problems with conductors and dielectrics for cryogenic cables
Abstract The most important problems which need to be solved if superconducting power cables are to be used on a large scale are connected with the superconducting cable materials and the dielectrics used for insulation. Research work on superconducting materials for ac and dc cables is briefly reviewed together with stabilization problems for these materials. Three types of insulation are considered - vacuum, subcooled or supercritical helium, and foil wound insulation. The merits and problems encountered in each case are discussed.
Measurement and Demonstration of Thermal Expansion Coefficient
There are many classroom demonstrations, such as the ball-and-ring experiment, for showing the existence of thermal expansion of solids. The coefficient of linear expansion α (= increase in length divided by the original length times the change in temperature) may be measured in high school laboratories using a number of methods.1–4 In this paper we describe an especially simple experiment for determining α for a metal rod. It is based on the well-known optical lever method and is suitable for either a laboratory experiment or a classroom exercise.