Helium leak detection in JET in the presence of high deuterium partial pressure

Abstract

Leak detection in JET (∼200 m3 volume, ∼8000 m length of welds, ∼300 bolted vacuum connections, base pressure at room temperature 2×10−9 mbar) had originally been based on the use of helium (4He) as a tracer gas. Later, high deuterium (D2) partial pressures due to D2 plasma operation made high-sensitivity leak testing by standard methods with 4He impossible; hence, alternative methods had to be developed. This eventually led to the use of a high-resolution Omegatron mass spectrometer able to separate D2 and 4He. Additional compression and selective pumping provides a sensitivity of 10−9 mbar l s−1. The advantages of the Omegatron system compared with other alternative methods will be presented. The use of a fully tritium compatible Omegatron in conjunction with ∼400 tracer gas tubes during the active phase leak detection will be discussed.