RF DEFOCUSING OF A SELF-FOCUSED BEAM IN A BEAM-GENERATED PLASMA.
STANFORD UNIV CA INST FOR PLASMA RESEARCH
Pagination or Media Count:
A beam injected into a region containing a low pressure neutral gas .0001 to .01 Torr creates a plasma by beam-neutral ionizing collisions. For radial plasma drainage, the equilibrium potential in the plasma decreases monotonically with radius and is a confining well for electrons, thus pinching the beam and confining it to the tube axis for some distance in the plasma. This process is known as ion focusing, or the electrostatic pinch effect. A second focusing process exists for partially or fully neutralized beams. This is the magnetic pinch effect and is the result of the self-magnetic field of the beam. At high beam voltage or perveance the magnetic forces exceed the electrostatic. Consequently, two regimes exist in which either the electrostatic or the magnetic pinch is the dominant beam focusing mechanism. Existing simultaneously with beam pinching are a number of processes which act to defocus or scatter beam electrons. For many common laboratory beams the most important is beam scattering as a result of radial rf electric fields accompanying the convective growth of noise fluctuations due to beam-plasma interaction. The purpose of this thesis is to compare theoretical and experimental results for beam defocusing due to this cause. Author
- Plasma Physics and Magnetohydrodynamics