Experimental investigation of flush-mounted electrostatic probes

Abstract

The behavior of flush-mounted electrostatic probes has been investigated in a pressuredriven, arc-heated shock tube over a wide range of shock tube freestream conditions and probe bias voltage. Measurements were made with large one-dimensional, flush electrostatic probes at initial shock tube pressures of 0.1 and 1.0 torr. Freestream electron densities ranged from 10 to almost 10 elec/cm. The flush electrostatic probes were biased at —3, — 15 and —90 v. The experimental results support predictions for which theories are available over the range of conditions corresponding to the case of sheath dimension small compared to the velocity boundary-layer thickness and frozen chemistry in the boundary layer. However, even at electron densities an order of magnitude below that for which the thinsheath assumption is valid, the deviation of the experimental data from theoretical predictions does not exceed the data scatter. The saturated ion current density collected by the probe was found to vary with the bias voltage raised to the one-half power.