Results 1 - 10 of 6771
Results 1 - 10 of 6771. Search took: 0.025 seconds
|Sort by: date | relevance|
[en] If the current sheet between adjacent twisted magnetic flux tubes is sufficiently thin, the electron flow velocity becomes comparable to the Alfven velocity and can destabilize collisionless Alfven waves. The threshold for instability in force-free plasmas is calculated for both inertial and kinetic Alfven-wave regimes. When there is strong magnetic shear, unstable kinetic Alfven waves can resonantly accelerate ions to energies much higher than the electron temperature. (c) 1999 The American Physical Society
[en] Space and astrophysical Alfven waves usually excist in a plasma containing thermal and nonthermal particles, and generally the thermal electron and ions have unequal number densities. Nevertheless, the linear properties of the waves are invariably assumed to be determined by a chargeneutral thermal plasma in the absence of the nonthermal particles, while the nonthermal particles cause growth or additional damping superposed onto the background model. Here, both analytic plasma theory and numerical solutions of the dispersion equation, unequal thermal electron and ion number densities (due to the presence of the nonthermal particles) may cause fundamental low wavenumber modifications to the Alfven modes, including the creation of a new resonance and severely modified dispersion. Thes results are found for both cold and warm plasmas. Previous work on Alfven waves should be re-evaluated in view of these results. (author). 6 refs.; 2 figs
[en] Geodesic acoustic modes (GAMs) in a tokamak excited by, for example, energetic particles can create a direct energy channel from energetic population to turbulence. In this paper, the ability of GAMs to further convert their energy into large scale motion such as zonal flows is investigated. The simplest case of GAMs, neglecting the effects of normal curvature, Alfven wave effect and drift effects, is considered. It is shown that such GAMs are stable with respect to generation of zonal flows.
[en] Alfven's critical ionization velocity hypothesis and some of the numerous experiments supporting it are briefly reviewed. The critical velocity is associated with a critical electric field, which may limit the transfer of RF power through a cold partially ionized blanket. The underlying mechanism is not fully understood at present, but experimental observation indicate the parameter and frequency ranges in which the phenomenon occurs. The upper frequency limit seems to be higher than the ion cyclotron frequency. For frequencies below the ion-neutral collision frequency, the field limitation becomes less severe