Magnetic Well Depth in EBT and Sensitivity to Hot Electron Ring Geometry

摘要

We examine the possibility that diamagnetic currents in the hot electron rings in the ELMO Bumpy Torus (EBT) plasma are strong enough to reverse gradients in line integral dl/B, thereby providing gross magnetohydrodynamic stability. Using a two-dimensional solution to the Grad-Shafranov equation with tensor pressure, we compute the electromotive force induced in a diamagnetic loop surrounding the EBT plasma. This allows direct comparison between calculated and measured diamagnetic loop signals for different values of perpendicular energy stored in the electron rings. Signals required for a local minimum in B and maximum in line integral dl/B are found to be sensitive functions of ring width for which there is presently no direct measurement. However, theoretical arguments provide estimates for the hot electron gyrodiameter (approx. 1.0 cm for 400 keV) and for the dispersion in guiding center drift orbits (1 cm for the measured ring length of 10 cm). Thus, a ring with a width of 2 cm or 2 gyrodiameters (full-width at half-maximum) and length of 10 cm requires a diamagnetic loop signal of 443 mV (W/sub perpendicular/ approx. 49 J and beta /sub perpendicular,max/ approx. 0.45) for a local maximum in line integral dl/B. (ERA citation 10:001652)