Plasma Physics (Physics/ECE/NE 922) Seminars

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Helicons, Whistlers, Lower Hybrid Waves: Physics of Wave Propagation and Absorption for Current Drive Via Landau Damping
Date: Monday, April 23rd
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Robert I. Pinsker, General Atomics
Abstract: In this seminar, I present the application of plasma waves in the lower hybrid range of frequencies (LHRF) for current drive in tokamaks. Wave damping mechanisms in a nearly collisionless hot magnetized plasma are briefly described, and the connections between the properties of the damping mechanisms and the optimal choices of wave properties (mode, frequency, wavelength) are explored. The two wave modes available for current drive in the LHRF are described and compared. The terms applied to these waves in different applications of plasma physics are elucidated. The character of the ray paths of these waves in the LHRF is illustrated in slab and toroidal geometries. Applications of these ideas to experiments in the DIII-D tokamak are discussed. Experiments are already underway using the 'helicon' wave (fast wave in the lower hybrid range of frequencies) at 0.5 GHz. The antenna/plasma coupling in the linear (very low power) regime of a 12-element 'comb-line' traveling wave antenna has been measured in tokamak discharges; a high-power system at ~1 MW power with a 30-element comb-line is in preparation. Experiments at a similar power level using the lower hybrid (slow) wave at 4.6 GHz are planned; the key feature of these experiments will be the location of the 'grill' wave-launcher on the high-field (small major radius) side of the torus to obtain much better wave accessibility to the core than would be possible using the conventional placement of the launcher on the low-field (large major radius) side at the outboard mid-plane.
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