PoloidalE×BDrift Used as an Effective Rotational Transform to Achieve Long Confinement Times in a Toroidal Electron Plasma

Electron plasmas with mean densities of 5.0×10⁶ cm^-3 have been confined for as long as 18 ms in a partially toroidal trap with a purely toroidal magnetic field (B₀=196 G, Rₒ=43 cm, a=5 cm). Confinement is limited to 2.0 ms unless feedback is employed to suppress the growth of a toroidal version of the $m=1$ diocotron mode. The confinement time is much longer than all characteristic single-particle drift time scales and therefore confirms the existence of an equilibrium in which the space-charge-generated E×B drift acts as an effective rotational transform.