The entry of a tenuous plasma into an axial magnetic field

A coaxial gun is used to inject a burst of energetic, low-density hydrogen plasma along the axis of the magnetic field produced by a long solenoid. The portion of this plasma which penetrates the magnetic field has a density of 10 11 -10 12 electrons/cm 3 and a mean directed energy of 10-20 keV. The properties of the plasma have been studied as it moves along the magnetic field. The mean ion velocity perpendicular to the magnetic field has been measured with Faraday Cups and the transverse energy of the plasma has been deduced from its diamagnetism. These measurements show that the transverse energy of the plasma resides predominantly in the ions which have considerable angular momentum. It is shown that this momentum is produced by electrons flowing from the vicinity of the vacuum chamber walls as the plasma enters the cusp-shaped field at the end of the solenoid.