Deduction of edge electron density with multiply charged ions in ORNL volume-type electron cyclotron resonance ion source.

The electron densities in the argon plasmas of the ORNL 6 GHz electron cyclotron resonance (ECR) ion source with a flat central magnetic field have been deduced from the ion branches of the electric probe current-voltage curves measured in the edge region of the plasmas. To overcome the difficulties due to unknown velocities of multiply charged ions at the sheath edge, a modified generalized Bohm criterion for the ion sheath velocity is introduced and the mean velocity of all ionic charge states at the sheath edge is assumed to be equal to the sound velocity of the system of particles. The calculated electron densities and temperatures for different plasmas optimized for four charge state distributions are discussed.

Three point method to characterize low-pressure electronegative discharges using electrostatic probe.

Electrostatic probe measurements for low-pressure inductively coupled SF(6) plasmas are performed. From the current-voltage (I-V) curves of probe, the saturation currents of the positive ions and electrons and the electron temperature are measured. The electronegativity and the negative ion density are deduced by using the ratios of these parameters at three adjacent pressure points. The positive ion density is calculated by the orbital-motion-limited theory, and the electron temperatures are given either by the slope of the I-V curves or by the electron energy distribution function with the second derivative of I-V curves. The variations in the charged species density with pressure and power are investigated.