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During high-power, long-pulse transmission from lower-hybrid-range-of-frequency (LHRF) antennas, the waveguide walls outgas as a result of rf-loss-induced heating. If the resulting pressure rise is too high, power transmission will be adversely affected and additional pumping may be required to maintain the pressure at a low enough value. The outgassing rates of waveguides made of various materials (oxygen-free high-conductivity copper, dispersoid copper, copper-coated carbon fiber composite, copper-coated graphite) were measured during rf injection at high power density s50-200 MW/m2d for a duration in the range 100�4700 s. The experiments were performed on a test-bed facility equipped with a 3.7 GHz klystron on multiwaveguide (2 to 18) mock-ups. The effect of the main parameters, namely, the waveguide surface temperature and the initial wall gas loading (�conditioning�), are analyzed in detail. It is concluded that an outgassing rate of 1 310-5 s5310-5d Pa m3 s-1 m-2 at 300 °C (400 °C) can be considered for most materials. The requirement, in terms of additional pumping, for the International Thermonuclear Experimental Reactor LHRF antenna is finally discussed.

Additional information

Authors: GONICHE M ET AL, Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA sur la Fusion, CEA Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: An article published in: Journal of Vacuum Science & Technology, Volume 23, Issue 1, pp. 55-65
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