Trapped-Particle-Mediated Damping and Transport

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Abstract
Weak axial variations in B(z) or φ(z) in Penning‐Malmberg traps cause some particles to be trapped locally. This causes a velocity‐space separatrix between trapped and passing populations, and collisional separatrix diffusion then causes mode damping and asymmetry‐induced transport. This separatrix dissipation scales with collisionality as v 1/2, so it dominates in low collisionallity plasmas. The confinement lifetime in the “CamV” apparatus was dominated by a weak magnetic ripple with δB/B ∼ 10−3, and it appears likely that the ubiquitous (L/B)−2 lifetime scalings and other applied asymmetry scalings represent similar TPM effects. TPM transport will limit the containment of large numbers of positrons or p̄s, since TPM loss rates generally scale as total charge Q 2, independent of length.

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