Experiments on the critical ionization velocity interaction in weak magnetic fields

The critical ionization velocity interaction is studied experimentally in a configuration with a magnetized plasma stream colliding with a stationary neutral gas cloud. In all previous experiments of this kind the magnetic field (1) has had a component transverse to the plasma flow and (2) has been strong in the sense that the electron gyro frequency, eB/m c , has exceeded or been approximately equal to the plasma frequency, w pc . Both these conditions play an important role in existing theories of the critical velocity interaction. The present experiments are performed to determine whether or not such interaction is possible when one of these conditions is not fulfilled, namely when the magnetic field is weak (eB/m e >>w pc ). Experiments have been performed both with a transverse and longitudinal (aligned with the plasma flow) magnetic field. It is found that in both cases the critical ionization velocity effect either disappears or becomes too small to be distinguishable among classical collisional processes.