Interaction of a Low Density Runaway Beam with Cavity Modes.
CALIFORNIA UNIV LOS ANGELES PLASMA PHYSICS GROUP
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An idealized problem is investigated which illustrates the role of wave-particle interactions in the evolution of runaway beams. The model considers the interaction between a weak cold beam, driven by an external static electric field E, and waves quantized by the geometry. The waves may correspond to Gould-Trivelpiece modes fixed by the length of the experimental device, or to the finite Fourier modes encountered in computer simulations. The physics consists of the sweeping of the accelerated beam through the resonance provided by each cavity mode. This process is formulated in analogy with the ONeil, Winfrey, Malmberg OWM problem but using a spatially averaged description based on the exact energy and momentum conservation laws with the dynamics simplified through a WKB representation of the dispersion relation. This model shows that the beam can be clamped in velocity with the momentum push being transferred to the waves. The model has been extended to the relativistic and multi-mode cases.
- Plasma Physics and Magnetohydrodynamics