Experiments on the Magnetic Field and Neutral Density Limits on CIV Interaction

Abstract A series of experiments on the critical ionization velocity (CIV) interaction in the impact configuration are reported, where the plasma density, the neutral density and the magnetic field strength have been varied. A combination of microwave interferometry and spectroscopy has been used to measure the plasma density and to study the electron energy distribution. The efficiency of the CIV process is evaluated as function of (1) the ratio between the Alfven velocity and the plasma stream velocity, and (2) the ratio between the ionization frequency and the ion gyro frequency. In the parameter range studied so far, efficient electron heating is found only when both these parameters exceed unity.