First measurements of neutrals pumping and of degassing rates of the hybrid coupler induced by HF power
Previous experiments have shown that large amounts of gas may be desorbed from the waveguide walls of a lower hybrid antenna. To reduce the pressure rise, a getter pump has been connected to the LH vessel of Tore Supra. The effective neutrals pumping speed of the LH launcher during a plasma shot has been measured for different configurations of the getter pump (inactive, low conductance and high conductance duct). For deuterium, an effective pumping speed of 33 m3/s was obtained. During short conditioning pulses and 2-s plasma shots, degassing rates were measured for RF power levels up to 1.2 MW. Degassing rates are documented with different filling gases (He, H(2), D(2)), and the effects of conditioning are discussed. This neutrals influx contributes to the particles balance of the plasma discharge: a significant increase of the total number of particles (10-20%) and a flattening of the density profile are inferred. A large increase of the neutrals pressure in the pumped limiter (up to 32%) was also observed. For 2-s shots, this pressure rise was held below 3 mPa at an average LH power density of 1.5 kW/cm2. However, this pressure rise may be, to some extent, larger in the reduced-section part of the launcher which has a low conductance. It is expected that this pressure rise should not exceed 5 mPa at full power (5 kW/cm2) after conditioning.
Bibliographic Reference: Report: EUR/CEA/FC/1384 FR (1989)
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199010909 / Last updated on: 1994-12-01
Original language: fr
Available languages: fr