Elektrische Sondenmessungen in schnellen, stromstarken Stoßentladungen

Abstract

In hot dense plasmas—as in the case of shock discharges—LANGMUIR probe measurements are difficult because complete probe characteristics are mostly unobtainable. Therefore, this work shows the possibility of getting information about the plasma at low probe voltages. It is shown that for a sufficiently small probe voltage the current drawn by a symmetrical plane double probe is proportional to ni/√Te (ni=ion density, Te=electron temperature). Knowing the approximate value of the electron temperature, the probe current gives the ion density immediately. Also the directed motion of ions can be determined by changing the orientation of the probe. A good time resolution (10-7 sec) was achieved by matching the impedance between the probe and the plasma to the coaxial probe circuit. The usefulness of this probe technique was investigated in a linear shock discharge with a coaxially, circular, plane double probe. Ion densities up to 1015 cm-3 and directed ion velocities of some 105 cm/sec were observed. Simultaneously the electrode voltage, current derivative, and the local azimuthal magnetic field in the plasma were measured.