AVS 45th International Symposium
    Vacuum Technology Division Monday Sessions
       Session VT-MoM

Paper VT-MoM9
Plasma Expansion in a Malmberg-Penning Trap as a Function of Background Pressure@footnote 1@

Monday, November 2, 1998, 11:00 am, Room 329

Session: Vacuum Gauging, Outgassing and Leak Detection
Presenter: E.H. Chao, Princeton University
Authors: E.H. Chao, Princeton University
R.C. Davidson, Princeton University
S.F. Paul, Princeton University
Correspondent: Click to Email
Single species nonneutral plasmas have very robust confinement properties because the conservation of canonical angular momentum in a system with azimuthal symmetry provides a powerful constraint on the allowed radial positions of the particles. If no external torques act on the plasma, the plasma cannot expand radially to the wall. However, collisions with a background neutral gas will exert a torque on the rotating plasma thus allowing the mean square radius to increase. In the EDG experiment at the Princeton Plasma Physics Laboratory, a pure electron plasma is confined in a Malmberg-Penning trap and the radial density profile is measured as a function of time. The base pressure is 5*10@super -10@ Torr and purified helium is injected to pressures @>=@1*10@super -9@ Torr. The magnetic field is varied between 100 and 600 Gauss. Plasma densities up to 3*10@super 7@ cm@super -3@ are achieved and temperatures are on the order of 1 eV. This leads to a Debye length of about 1 mm while the plasma dimensions are 1-2 cm in radius and 15 cm in length. The expansion rate of the plasma in the presence of a background neutral gas has been studied theoretically by Davidson, et al.@footnote 2,3@ The expansion rates observed experimentally are faster than the theoretical prediction but the magnetic field scaling of the expansion rate is similar. In addition, using the measured radial density profiles along with a numerical code to calculate the axial density distribution, the decrease in electrostatic energy was calculated and compared with the predicted temperature rise in Ref. [3]. Finally, measurements of plasma expansion rates as a function of background gas pressure are in progress. @FootnoteText@ @footnote 1@Research supported by the Office of Naval Research. @footnote 2@R.C. Davidson and D.A. Moore, Phys. Plasmas 3 (1996) 218. @footnote 3@R.C. Davidson and E.H. Chao, Phys. Plasmas 3 (1996) 2615.