Experimental investigation of standing wave interactions with a magnetized plasma in a minimum-B field

Standing waves in the microwave regime are generated by a superposition of forward and backward moving waves induced by reflections from geometrical transitions in the plasma vacuum boundary. The waves are preferentially damped in the weakly collisional (νen/ω congruent with 10-4) plasma near the launch region (∼3-15 cm), where the electron temperature has a higher than average value (Te>Teavg∼12 eV). Typical e-folding damping lengths are of the order of 10 cm, and depend upon the wave power and plasma collisionality. Fourier spectrum of the standing waves indicates about 23% downshift in the vacuum wave-number due to plasma dispersion. Electron trapping is observed in the potential troughs of the waves.