Magnetic field dependence of asymmetry-induced transport: A new approach

Abstract

A new technique is used to experimentally study the dependence of asymmetry-induced radial particle flux Γ on an axial magnetic field B in a modified Malmberg–Penning trap. This dependence is complicated by the fact that B enters the physics in at least two places: in the asymmetry-induced first order radial drift velocity vr=Eθ∕B and in the zeroth order azimuthal drift velocity vθ=Er∕B. To separate these, it is assumed that the latter always enters the physics in the combination ω−lωR, where ωR(r)=vθ∕r is the column rotation frequency and ω and l are the asymmetry frequency and azimuthal mode number, respectively. Points where ω−lωR=0 are then selected from a Γ versus r versus ω data set, thus insuring that any function of this combination is constant. When the selected flux is plotted versus the density gradient ∇n, a roughly linear dependence is observed, showing that the assumption is valid and that the diffusive contribution to the transport has been isolated. The slope of a least-squares fitted line then gives the diffusion coefficient D0 for the selected flux. Varying the magnetic field, it is found that D0∝B−1.33±0.05. This does not match the scaling predicted by resonant particle transport theory.