Experimental study of a current sheet

Abstract

A very thin current sheet is produced by induction, supporting a β = 1 plasma. It is found to be stable for a period of time, which depends on density, and is longer than expected from existing theories of resistive tearing instability. At the end of this period, the sheet is rapidly destroyed. This destruction occurs when the electron density is lower than a critical value: an initial breakthrough at one point gives rise to a magnetic field across the sheet which drives the whole current layer out of equilibrium. It is shown that this breakthrough cannot be produced either by unstable ion drift waves or by electrons of the plasma running away, as already observed in other experiments. A new mechanism is needed to explain these results.