Onset of Anomalous Plasma Resistivity after Application of a Step Electric Field

A photoionized argon plasma was subjected to a step E field of the order of 10−2 V/cm (1<E/Eτ<80,where Eτ is the runaway field). In a magnetic field free plasma the electron current rose linearly to a maximum value (the time of which varies as E−1/2) and then fell as the result of the rapid growth (in a few wave periods) of ion wave turbulence (consisting almost entirely of waves traveling at large angles to the E field). In the presence of a magnetic field parallel to E (zero to 150 G) the time of the current maximum decreased by 40% to a minimum at 40 G (presumably due to finite geometry effects) and then rose almost linearly from this point by a factor of 2 at 150 G. Wave propagation was still at large angles to E. Parameters were 4×108<n<4×109ions/cm3; kTe≃0.36 eV; kTi≃0.025 ev.