Investigation of lower hybrid wave damping in the PBX-M tokamak
- Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)
Lower hybrid (LH) current drive experiments on the Princeton Beta Experiment-Modified (PBX-M) [Phys. Fluids B {bold 2}, 1271 (1990)] have shown that the current profile can be changed by varying the phase velocity of the waves. The radial profile of the current carrying electrons was deduced from two-dimensional hard x-ray tomography. For a certain range of phase velocities, there is a correlation between the peak of the fast electron profile and the launched wave spectrum, despite the presence of a wide spectral gap between the phase velocity and the thermal electron energy distribution. A new model is proposed to explain how first-pass wave damping is possible in such plasmas. The rf power can form a tail of energetic electrons, and subsequently waves with moderate phase velocity can damp on them. For waves with very fast phase velocity, there must be an upshift of the n{sub {parallel}} spectrum for any damping to occur. These hypotheses are supported by ray tracing results which are coupled to relativistic Fokker{endash}Planck calculations of the electron distribution function. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 435175
- Journal Information:
- Physics of Plasmas, Vol. 4, Issue 1; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
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