EXPERIMENTAL-VERIFICATION OF THE LOW-FREQUENCY DRIFT INSTABILITY IN AMAGNETIZED RING DISCHARGE

The two-dimensional radial and azimuthal electron temperature and dens ity distributions in a magnetized ring discharge (B = 100-190 mT, P(He ) = 3-6 Pa, 3 eV < T-e < 15 eV, 10(18) m(-3) < n(e) < 2 x 10(19) m(-3) ) are obtained from measured intensity ratios of the Hel lines 447.15 nm, 471.31 nm, 492.19 nm and 587.56 nm, using a calibrated ICCD camera system. Dynamical plasma emission imaging (DPEI) represents a new dia gnostic tool for studying not only the stationary parameters but also the electron temperature and density oscillations induced by a coheren t low-frequency instability. The phase shift between temperature and d ensity oscillations, as well as the radial profiles of the oscillation amplitudes, may be determined. These features characterize a prominen t type of drift instability arising in an inductively coupled rf disch arge with an axial magnetic field superimposed where the radial electr on temperature and density gradients are in opposite directions. Numer ical simulations recurring to the measured plasma densities and temper atures help to clarify the anomalous transport leading to a degradatio n of plasma confinement.