A Investigation of RF Driven Currents in a Magnetized Plasma Using a Slow Wave Structure
An investigation of the interaction of electrostatic waves launched by a slow wave structure with a magnetized plasma is made. The characteristics of the electrostatic waves and the electron dynamics are studied experimentally. Of primary experimental interest is the measurement of the electron energy distribution and the rf-induced electron flux along the background magnetic field. This interest is motivated by a need for a more complete understanding of interaction of plasma with a slow wave electrostatic field which is of importance of rf-heating and rf current drive in fusion plasmas. Electrostatic waves are launched from a slow wave structure near the low density periphery of a magnetized plasma column that possesses density gradients in both the radial and axial directions. The axial inhomogeneity is found to significantly complicate the picture of wave propagation. It is found the waves launched along the background magnetic field into a region of increasing electron density can experience a reflection as the wave propagates into the plasma interior. Significant increases in the effective electron temperature and rf-induced axial electron flux near the plasma surface are observed using an electrostatic energy analyzer and current probes. The lower-hybrid resonance layer as determined by the observations of large radial phase changes using rf probes in this region correspond approximately with the radial location of increased electron temperature and rf-induced electron flux. The increase in effective electron temperature can be attributed to the coherent oscillations of the resonant electrons in the wave field as derived from the quasilinear theory. The rf-induced electron flux can be interpreted as the nonlinear ponderomotive force on electrons due to the parallel gradient of the electric field energy. The experimental results are in qualitative agreement with theory.
- Pub Date:
- PONDERMOTIVE FORCE;
- QUASILINEAR THEORY;
- Physics: Fluid and Plasma