Experimental realization of nearly steady-state toroidal electron plasmasa

Electron plasmas with densities of 5 × 10 6 cm − 3 are trapped in the Lawrence Non-neutral Torus II (LNT II) for times exceeding 1 s. LNT II is a high aspect ratio ( R 0 / a ≳ 10 ) partially toroidal trap (270° arc, B 0 = 670 G ). The m = 1 diocotron mode is launched and detected using isolated segments of a fully sectored conducting boundary and its frequency is used to determine the total trapped charge as a function of time. The observed confinement time ( ≈ 3 s ) approaches the theoretical limit ( ≈ 6 s ) set by the magnetic pumping transport mechanism of Crooks and O’Neil [Phys. Plasmas 3, 2533 (1996)]. We also present equilibrium modeling and numerical simulations of the toroidal m = 1 mode constrained by experimental data. Future work includes the identification of the dominant transport mechanisms via confinement scaling experiments and measurement of the m = 2 mode frequency and development of a strategy for making a transition to fully toroidal confinement.