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Abstract

During high power transmission in waveguides (rho = 1-10 kW/cm2) of radio frequency waves, strong outgassing may be observed. This outgassing can be due to breakdowns or, for long pulse shots, to a thermal baking of the waveguide walls provided by the RF losses. Breakdowns depend strongly on surface state, namely on secondary electron emission coefficient and also on adsorbed molecules coverage. During the conditioning phase, outgassing flux varies between 1.0 * E-3 T.l/s and 1.0 * E-1 T.l/s per breakdown. RF losses-induced outgassing may be very large for long pulses (t(RF) greater than 30 s): for a 63 s pulse, ultimate outgassing rate lies between 1.0 * E-8 T.l.s(-1) /cm2 and 1.0 * E-5 T.l.s(-1) /cm2. These strong variations are related to initial treatment and RF conditioning. The global activation energy is found to be relatively constant after a few RF shots (approximately equal to 23 kcal/mole).

Additional information

Authors: GONICHE M, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);DEMERS Y, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);REY G, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);SEKI M, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR);TONON G, CEA, Département de Recherches sur la Fusion Contrôlée, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Paper presented: Journée d'Etude sur le Dégazage, Société Française du Vide, Paris (FR), June 2, 1992
Availability: Available from (1) as Paper FR 37245 ORA
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