Fluctuations in electron cyclotron resonance plasma in a divergent magnetic field

Abstract

The dependence of fluctuations on electron-neutral collision frequency (V_en) and the radial location is investigated in an electron cyclotron resonance plasma in a divergent magnetic field region for a set of magnetic fields. Results indicate that the fluctuations depend strongly on the collision frequency. At lower magnetic fields and V_en, the fluctuation levels are small and are observed to peak around 3–5 cm from the central plasma region. Coherent wave modes are found to contribute up to about 30% of the total fluctuation power, and two to three harmonics are present in the power spectra. There are two principal modes present in the discharge: one appears to be a dissipative mode associated with a collisional drift wave instability initiated at a lower pressure (collision frequencies) (∼0.5mTorr) and is stabilized at a higher pressure (≳3mTorr). The other mode appears at intermediate pressure (≳1.75mTorr) and possesses the signature of a flute instability. The fluctuation levels indicate that flute modes are predominant in the discharge at higher pressures (>1.75mTorr) and at higher values of the magnetic field (∼540 Gauss).