Stark Broadening of Two Ionized-Helium Lines by Collective Electric Fields in a Laboratory Plasma

Profiles of the He II 4686- and 3203-Å lines observed during the passage of the imploding current sheath in a high-velocity, low-density $\theta$ pinch show a broadening that at early times is not due to the usual mechanisms (Doppler, Holtsmark, or Zeeman effects). Most of this broadening is therefore interpreted as due to Stark effects caused by suprathermal collective field fluctuations, and at later times as due to a combination of these and Doppler effects.