The structure of electromagnetic perturbations in a magnetic neutral sheet is analyzed within the framework of a Vlasov-Maxwellian picture. In reference to Harris' equilibrium state, a boundary value problem is formulated and solved to give the possible existence of a low-frequency electromagnetic wave of compressional type, propagating along the electron-drift current in the sheet. The stability of this mode is critically dependent on the thickness parameter of the sheet. If the sheet is thin enough, the perturbation will grow even for T
e = T
i. The critical thicknesses are calculated with regard to various temperature ratios and their values are found to be about 0.9r*Li or less, where r*Li means the ion Larmor radius just outside the sheet region.
By evaluating the exact population difference between resonant electrons with velocities smaller and larger than the phase velocity, a correction to Landau damping proportional to the square of the wave amplitude is obtained theoretically.
A tokamak edge plasma significantly absorbs ICRF waves when a cutoff-resonance-cutoff is present in the evanescent region. Two ion component plasmas in a torus are considered although the plasmas are modelled by a slab. The absorption rate Ab is roughly given by M2 for 1 ≫ M2 > S2 and S4 for 1 ≫ S2 > M2, where M = kyℓ and S ≅ kzℓ and ℓ is a scale-length of the order of the plasma minor radius, and ky and kz are the perpendicular and the parallel components of the wave vector. It is noted that M and S become of the order of unity. Since Ab is not very sensitive to the density ratio of the two ion species, a few per cent of impurities may cause significant absorption. As the mass ratio of the two ion species comes close to unity, the triplet forms readily. Therefore, a D-T plasma seems to suffer more easily from this kind of resonance absorption than a D-H plasma.
The effects on Alfven waves of a rarefied plasma layer surrounding a cylindrical main plasma are investigated. The plasma is approximated with a two-step density profile and is assumed to be surrounded by a conducting wall. When the Alfvén resonance exists inside the rarefied plasma layer, two new modes are generated. One has its maximum of the wave intensity at the wall and is thus similar to a surface wave, and the other is a type of coaxial mode. These results are re-examined in a diffuse boundary plasma and the presence of these modes is confirmed.
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