RUI: Equilibrium, Stability, Dynamics, and Transport Physics for Electron Plasma in a Toroidal Magnetic Field

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Prior NSF support was used to design and construct a new high performance toroidal trap for non-neutral plasmas (i.e. plasmas with a single sign of charged particle). In the past year, construction of the experiment was completed and early experiments conducted in a portion of the torus produced nearly steady state plasma conditions (several second confinement times). The present award permits the P.I. and his undergraduate students to explore the physics of long-lived toroidal non-neutral plasmas in much greater detail. The non-uniform character of the toroidal magnetic field in this experiment is predicted to ultimately limit the confinement to times on the order of ten seconds. Experiments will be conducted to identify the loss mechanism predicted by this as yet untested theory. Additional experiments will be conducted to identify the effect of the curved and non-uniform toroidal magnetic field on the natural modes of oscillation (i.e. waves) that propagate in non-neutral plasmas. In addition, the present award will fund development of instruments and techniques necessary to transition from (and diagnose) experiments in a portion of the torus, to confinement in the full torus. Experiments in which non-neutral plasmas are isolated for long times so that they can be observed and manipulated provide excellent "wind tunnels" for close testing of plasma and neutral fluid theories; helping refine our fundamental understanding of naturally occurring fluid systems and plasmas and of laboratory plasmas that find application in society. Non-neutral plasmas can be generated reproducibly and confined for very long times in traps with a simple geometry (i.e. a cylinder). However, until construction of the present device was completed, attempts to trap non-neutral plasmas in more complicated magnetic field arrangements (such as a torus) have resulted in very short trapping times (of order 100 microseconds). No other existing experiment is poised answer fundamental questions about the criteria for stable equilibrium states, the toroidal effects on plasma dynamics, and the limitations on confinement for such systems. The activity funded under this award will provide research experiences (as well as scientific authorship and presentation opportunities) for undergraduate students, inspiring some of them to pursue graduate work in physics. The apparatus will also be used to recruit promising high school students to the Lawrence University physics program and expose the campus and local communities to the subject of plasma physics.