INITIATION OF EXTENDED ARC DISCHARGE IN ICF REACTOR DENSE ATMOSPHERES (STREAMER PROPAGATION, SPARK GAP, PREIONIZATION, BOLTZMANN EQUATION SOLVER)

Reduced density plasma channels are essential for LIB transport from external diodes to an ICF pellet centered in the 2-4 MPa superheated steamfilled cavity of the Heavy Water ICF Reactor. Forming such channels by ohmic heating requires the initiation of straight arc discharges along each beamline. The goal of this thesis is to evaluate the threshold beamline preionization and applied electric field for arc initiation.; The capability of several preionizers to produce a straight preionized trail is evaluated through a ten-group Boltzmann equation solver. Electron densities around 10('17) m('-3) could be maintained in the trail by monojoule output external preionizers. Trail preionization through the co-application of UV and CO(,2) lasers appears to be the most promising technique. UV laser preionization of NO(a('4)(pi)) formed in the fireball shows also good prospective. The large divergence of soft X-ray sources reduces their attractivity.; The E/N dependent electron transport properties are used to construct the first streamer model capable of evaluating the steady-state streamer wave shape. Results from this variational principle model are comparable to asymptotic wave shapes obtained from 2-D time dependent simulations. The streamer propagation speed dependence on the electric field and the neutral density was evaluated for D(,2)O vapor through this model. The formation of highly conductive filament along the beamline axis seems to be caused by thermal detachment instability of the streamer-induced OD('-) population.; The streamers-induced highly ionized filament transition into a multi-kA carrying plasma channel is simulated by a modified radiation-MHD one-dimensional code. Parametric study of the initial filament conductivity effect on the current history indicates that above threshold conductivity, kA arc will develop. The threshold conductivity increases three fold to counter radiation losses while the jXB force accelerate the current rise.; It is shown that electric field of 1 MV/m can convert a preionized trail in dense superheated D(,2)O vapor into a multi-kA-carrying arc discharge within 10 sec, provided that 0.2 mm radius filament having center electron density of 1.5*10('21) m('-3) is formed due to the streamers propagation.