Confinement Time Exceeding One Second in a Toroidal Electron Plasma

Pure electron plasmas ($n=2\times 10^7$ cm$^{-3}$, $a=1.27$ cm, $R_p=17.4$ cm) are confined for times exceeding one second in a new toroidal device, the Lawrence Non-neutral Torus II. The plasma is trapped in a 270$^{\circ}$ toroidal arc by application of gate potentials to sections of a sectored gold-plated toroidal boundary ($b=3.81$ cm, $R_0=18$ cm). At base vacuum pressures below $10^{-8}$ torr and magnetic field strengths approaching 700 gauss, the $m=1$ diocotron mode is excited by applying several cycles of rf near the resonant frequency to a section of the wall. The $m=1$ frequency, which is approximately proportional to the trapped charge, decays on a three second timescale, a confinement time that exceeds by at least an order of magnitude the confinement observed in all other toroidal traps for non-neutral plasmas. Numerical simulations that include toroidal effects are employed to accurately extract plasma charge and $m=1$ mode amplitude from the experimental data. Future work will include attempts to withdraw the electron source in order to study confinement in a full torus. This work is supported DOE-NSF Grant 0317412.