Dependence of enhanced asymmetry-induced transport on collision frequency

作者：Eggleston D L^*

来源：Physics of Plasmas, 2014, 21(7): 072318.

DOI：10.1063/1.4891661

A single-particle code with collisional effects is used to study how asymmetry-induced radial transport in a non-neutral plasma depends on collision frequency. For asymmetries of the form phi 1(r) cos(kz) cos(omega t - l theta), two sources for the transport have been identified: resonant particles and axially trapped particles. The simulation shows that this latter type, which occurs near the radius where omega matches the azimuthal rotation frequency omega(R), is usually dominant at low collision frequency nu but becomes negligible at higher nu. This behavior can be understood by noting that axially trapped particles have a lower trapping frequency than resonant particles. In the low nu (banana) regime, the radial oscillations have amplitude Delta r approximate to v(r)/omega(T), so axially trapped particles dominate, and the transport may even exceed the resonant particle plateau regime level. As nu increases, collisions start to interrupt the slower axially trapped particle oscillations, while the resonant particles are still in the banana regime, so the axially trapped particle contribution to the transport decreases. At the largest nu values, axially trapped particle transport is negligible and the observed diffusion coefficient matches that given by plateau regime resonant particle theory. Heuristic models based on these considerations give reasonable agreement with the observed scaling laws for the value of the collision frequency where axially trapped particle transport starts to decrease and for the enhancement of the diffusion coefficient produced by axially trapped particles.

• 出版日期2014-7