Development of cryogenic electrical components for the demonstration poloidal coils

Several cryogenic electrical components have been developed for the Demonstration Poloidal Coils (DPC) in Japan Atomic Energy Research Institute (JAERI). The test coils of the DPC were designed for high-voltage and forced-cooled conductors. The rated voltage of each coil is AC 6.9 kV. Maximum operating pressure is 20 atm. JAERI is developing and evaluating (1) insulation coupling, (2) instrumentation cable with new insulator, (3) a feedthrough for high voltage use, (4) a high-voltage isolation amplifier and (5) an amorphous silicon thermometer for use in high magnetic fields. The insulation coupling and feedthrough are designed on the specification of testing voltage AC 16 kV, testing pressure 30 atm and 1 × 10^-6Acc/s helium leakage. The insulation coupling consists of glass-cloth-epoxy and stainless steel pipes. The feedthrough is made with ceramics. We usually use Teflon or polyimid (KAPTON) tape insulator for instrumentation cables at cryogenic temperatures. However, Teflon is not strong against irradiation and polyimid tape does not have a sufficient high voltage performance because of a withstanding corona. Therefore, poly-ether-imid (PEI) is selected because of its irradiation and corona withstanding. Amorphous silicon thin film has a good sensitivity in the range of 4 K - 30 K and exhibits few magnetic field influences. The stability of amorphous silicon may be high because amorphous silicon has good mechanical and chemical properties. This element can be applied to thermometers in a high magnetic field environment.