Modification of low frequency instabilities in a toroidal plasma

Low frequency (LF) electrostatic fluctuations have been observed in toroidal device BETA. We have made an attempt to study the modification of these LF fluctuations by shining large amplitude oscillating electric field near upper hybrid frequency and heavier ion mass gas. The influence of a high frequency pump wave on low frequency (LF) electrostatic flute type instabilities is investigated using a pump frequency (fo) at 2.45 GHz with a μ-wave source of 700 W, launching Ordinary mode. To see the effect of ion mass on low frequency (LF) electrostatic instabilities, hot cathode discharge produced plasma of argon, krypton and xenon gas in studied with similar experimental parameters to ensure identical plasma conditions. Measurements reveal that fluctuation in density and floating potential get significantly suppressed with higher ion mass. A shift in the frequency of the fluctuating component to a lower frequency value with increase in ion mass is observed. These measurements suggest an inverse dependence of observed frequency on M2/3ion. (author). 5 refs, 4 figs