Abstract:
The results of laboratory experiments on the impulse current spreading from the spherical electrodes and the breakdown occurring in quartz sand of various humidity at the impulse voltages of $20$–$40$ kV are presented. It is shown that, at the current densities on the electrode above some critical value, a sharp nonlinear decrease of the impulse grounding resistance occurs, an ionization-superheating instability develops, and thus the current contraction takes place and a plasma channel in the soil occurs. A method is proposed to determine the critical strength of the ionization electric field. It was discovered that, at long discharge gaps in humid sand, the breakdown develops with a long time delay, similarly to thermal breakdown.
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