Unstable particle drift across a magnetic field caused by oblique electric field gradients

Abstract

The presence of a positive electric field gradient e dE/dx>0 oblique to a uniform magnetostatic field is shown to cause unstable particle motion across the magnetic lines. Both the drift velocity along ∇E and the E×B drift velocity exponentiate in time with growth rate proportional to |dE/dx|1/2 sin θ, where π/2−θ is the angle between E and B. Thus the cross-B transport due to ∇E is more severe than the ∇B and ∂E/∂t effects, that cause constant drift velocity under uniform field variation. The result has implications to a variety of situations involving oblique electric gradients, such as magnetized plasma sheaths, large amplitude drift waves, and possibly tokamak edge transport.