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

Eggleston, D. L.; Williams, J. M.
March 2008
Physics of Plasmas;Mar2008, Vol. 15 Issue 3, p032305
Academic Journal
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.


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