Neoclassical transport processes in weakly collisional plasmas with fractured velocity distribution functions

Abstract

Ripples in magnetic or electrostatic confinement fields give rise to trapping separatrices, and conventional neoclassical transport theory describes the collisional trapping/detrapping of particles with fractured distribution function. Our experiments and novel theory have now characterized a new kind of neoclassical transport processes arising from chaotic (nominally collisionless) separatrix crossings, which occur due to E × B plasma rotation along θ−ruffled or wave-perturbed separatrices. This chaotic neoclassical transport becomes dominant at low collisionality when the collisional spreading of particle energy during the dynamical period is less than the separatrix energy ruffle.

Superbanana transport in the collisional heating of a plasma column forced across a squeeze potential

“…In previous works on superbanana transport that caused cross-magnetic field particle loss, it was observed that a "ruffle" on the separatrix, i.e., a h asymmetry, could enhance the transport with a loss rate scaling as 0 . 4,5,[16][17][18] This enhanced transport is caused by an effective broadening of the boundary layer at the separatrix as the ruffle allows particles to chaotically trap and detrap. We believe that a similar effect could be observed in the heating process considered here.…”

“…This geometry has been considered previously in studies of superbanana transport that involves the damping of low-frequency drift waves (trapped particle diocotron modes) [13][14][15] and crossmagnetic field particle transport. 4,5,[16][17][18][19] In those cases, cross-magnetic field drifts and plasma rotation were necessary ingredients in the theory. Here, these effects can be ignored, further simplifying the analysis.…”

Electron cyclotron resonance (ECR) magnetometry with a plasma reservoir

“…Note that the potentials applied during the extraction of a target plasma resemble the "squeeze" potentials employed by the UCSD group to study transport effects. [40][41][42] They explain that squeeze-driven transport comes from particles quasi-trapped on one or the other side of the squeeze. These particles drift for many orbits before recrossing the squeeze separatrix.…”