Fast ionisation waves under electrical breakdown conditions

An analysis of experimental and theoretical investigations is the basis of this state-of-art review of models of fast ionisation waves (FIWs) and of characteristics and properties of these waves. The attention is concentrated on waves with the maximum possible velocities of 10⁹—2×10¹⁰ cm s^—1 when the amplitudes of voltage pulses are 20—300 kV. At low and moderate pressures the reduced intensity of the electric field in the front of a wave is so high that the front becomes a moving source of a beam of high-energy electrons in which the current can reach several kiloamperes. At moderate pressures the high-energy electrons in the wave front overtake the front and cause preliminary ionisation of the gas ahead of the front. At low pressures these electrons determine mainly the mechanism of the motion of the front. At high pressures (in excess of 200 torr) the main source of such preionisation is the radiation emitted by the front. The high rate of filling of the discharge volume with a plasma, high electric fields and high energies of the electrons in the front, and the slight heating of the gas make fast ionisation waves attractive for applications.