Spectroscopic investigation of plasma turbulence

Optical studies of plasma fluctuations have been carried out in a toroidal, high-voltage discharge—the Plasma Betatron experiment at the University of Saskatchewan. Following the formation of the helium plasma, of density 1019–1020 m−3, by rf preionization and a preheating field, the electric field (≤ 8 kV/m) of the main discharge is applied parallel to the steady toroidal magnetic field of 0.3 T. Forbidden lines and satellites observed near the He I 21P–41D (4922 Å) and 23P–43D (4471 Å) lines show that low [Formula: see text] and high (ω ~ ωpe) frequency fluctuations are present at early times (t < 2 μs). The rms field strengths are comparable, at [Formula: see text]. An analysis is given of the possible role of these fluctuations in the rapid thermal transport previously observed from the current skin layer to the interior of the plasma. Direct energy transport by propagating electron plasma or ion acoustic waves is shown to be insignificant. However, the low frequency field strength is sufficient to allow for an explanation in terms of enhanced thermal diffusion due to lower hybrid waves.