Timothy Nelson Good

Test-ion diffusion in a magnetized plasma

Cross-field transport of barium test ions is studied in a Q-machine plasma. Test particles are produced and tracked in their motion by an optical tagging method. The comparison between the measured tag signal and a simple theoretical simulation yields an evaluation of the ion diffusivity. Diffusion is supported by classical mechanisms. The injection of different noble buffer gases modifies the plasma parameters in such a way that the diffusion remains classical but its magnitude is reduced. >

Partial line‐tying of the flute mode in a magnetic mirror

The amount of electron emission required to partially line‐tie the m=1 flute mode is measured on an axisymmetric mirror‐confined plasma. The results are consistent with an ideal magnetohydrodynamic (MHD) calculation with a sheath dissipation term added. The minimum electron emission required is approximately the ion saturation current. The sheath impedance is also calculated for the case when the electron emission exceeds the threshold required for the formation of a virtual sheath.

Ion confinement in a simple mirror stabilized by surface line tying

Experiments were conducted using a barium plasma in a simple axisymmetric mirror machine that was stabilized against the magnetic curvature‐driven interchange mode by surface line tying. Ion cyclotron resonance heating was applied to heat ions, producing a mirror‐trapped ion population. The ion‐velocity distribution function was diagnosed nonperturbatively by using laser‐induced fluorescence techniques. The rf heated distribution was a non‐Maxwellian in fI(v⊥), and a sloshing distribution in fI(v∥). When the plasma source was cut off, the plasma decay was studied to determine the confinement properties of the plasma afterglow and the effects of the stabilizing blanket. Mirror‐trapped ions were lost axially at the classical ion–ion collision rate. Analysis of the temporal evolution of radial profiles of ion‐energy density, in the afterglow, indicates that axial loss rates dominanted over radial losses.