electron emission from the insulator, the electron collision leads to desorption and ionization of gas sorpted on the insulator. The ionized particles impinge on the conductor and supply additional electrons. The multiplication rate, Z, is formulated following: where yc and ys are the emissive yields of the secondary electron due to ion collision with the conductor and due to electron collision with the insulator, respectively. The n is estimated as Zt//h. The emitted electron from the conductor due to the ion collision impinges on the insulator in the probability, Pcs. Z=1 means breakdown condition [11]. Though we can avail knowledge for the electron-simulated desorption (ESD) [12], which is one of the surface analysis techniques, as for o, Q and s, we have data for only a few materials. The Z is sufficiently over unity at the condition of our experiment, where Pcs = 0.1, yc=0.1, ys = 2, n = 20, <7=Zx 1018m~2, Q=ZxlO-24m2 and 5=100. It is noted the <7 and Q for the insulator are substituted by ones of tungsten and s by alumina. It is necessary that the collision energy of the hopping electron must exceed the thresholds of both ESD and multi-emission of the secondary electron on the insulator. The former threshold is approximately 20 eV and the latter about 50 eV. The electron avalanche leaves positive charges on the insulator and diminishes the potential ramp at the transition region so that the discharge is terminated. Decrease of the sorpted gas due to multi-collision of electron (the total cross-section for ESD is two orders larger than the ionic one) also breaks positive feedback of self-sustained discharge. Additional plasma generated from the desorpted
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