Confinement Asymmetry and Trapped Particle Effects on Radial Transport in Charged Plasmas

Weak axial variations in B(z) or Φ(z) in “axisymmetric” plasma traps cause a fraction of the particles to be trapped axially, with a velocity-space separatrix between trapped and passing populations. The trapped and passing particles experience different dynamics in response to a variety of θ-asymmetries in the E × B rotating plasma, so a discontinuity in the velocity-space distribution f(v) tends to form at the separatrix. Collisional scatterings thus cause large fluxes as they smooth the distribution in a boundary layer near the separatrix. In essence, this separatrix dissipation damps the AC or DC longitudinal currents induced by plasma waves or confinement field asymmetries. This trapped-particlemediated damping and “neoclassical” particle transport often dominates in cylindrical pure electron plasmas, and may be important in other nominally symmetric open systems.