The introduction of a plasma and a strong guide magnetic field in a free electron laser (FEL) slows down the phase velocity of radiation, significantly reducing the requirements on beam energy for generating frequencies below the electron-cyclotron frequency (oi, < oj,). Around plasma resonance (cu, ~ w p), the FEL mode couples to two-stream instability (TSI), attaining a large growth rate, comparable to that of the wiggler-free TSI. At plasma densities comparable to beam density, the beam-induced local depression in the electron density of the plasma acts as a waveguide for guiding any high-frequency radiation when the beam current is l h > 17 kA.
For three tokamaks, the local cross-field particle transport time at the edge is observed to be of the order of the local sound transit time along the magnetic field. Static equilibria as conventionally defined in magnetohydrodynamics are therefore inapplicable. It is shown that when plasma transport is poloidally asymmetric, the steady state necessarily involves parallel flows comparable to the sound speed, with significant density modulations along a given flux surface. Such sonic parallel flows can precipitate the parallel shear flow instability, with attendant large fluctuations and momentum transport. The consequences of such a loss of static equilibrium are explored.
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