Laser-initiated, reduced density channels for transporting charged particle beams

A charge particle beam driven inertial confinement fusion reactor will require reduced density current carrying channels through the gas blanket to transport the beams from the diodes to the target. We have created suitable reduced density channels in air at atmospheric pressure by guiding an electric discharge with laser-induced, aerosol-initiated air-breakdown. The resulting channel, which is no longer current carrying, stabilizes about 30 microsec after the electric discharge at a radius of about 1 cm, a temperature of about 5000 K, a gas density of about 10 to the 18th power/cu cm and an electron density of about 10 to the 14th power/cu cm. After about 100 microsec, the channel becomes turbulent and expands further. We provide estimates of the diminishing temperature and increasing density during this later phase. The desired reduced-density, current carrying channel can be produced by a second fast rising, high current discharge on the described channel, after the stable reduced density conditions have been achieved.