Observations of propagating double layers in a high current discharge.

Observations of current disruptions and strong electric fields along the magnetic field in a high-density (2×10¹⁹ m^‑3), highly-ionized, moving, and expanding plasma column are reported. The electric field is interpreted in terms of propagating, strong electric double layers (3–5 kV). An initial plasma column is formed in an axial magnetic field (0.1 T) by means of a conical theta-pinch plasma gun. When an axial current (max 5 kA, 3–5 kV) is drawn through the column spontaneous disruptions and double-layer formation occur within a few microseconds. Floating, secondary emitting Langmuir probes are used. They often indicate very high positive potential peaks (1–2 kV above the anode potential during a few μs) in the plasma on the positive side of the double layer. Short, intense bursts of HF radiation are detected at the disruptions.