Experimental results from TMX-U

This paper presents the recent results from the Tandem Mirror Experiment-Update(TMX-U). Many of these results can be divided into two major areas: (1) axial confinement and plasma potential, and (2) radial transport and total confinement (i.e., particle balance). Among the key observations to be discussed are the following: When the ion-confining potential θ/sub ic/ is small, θ/sub ic//T/sub i/ ∼ 1 to 2, the axial confinement time scales as the theoretical Pastukhov time. Deep thermal barriers (θ/sub b/ ∼ 0.7 kV, θ/sub b//T/sub e/ ∼ 6 to 7) have been measured, but there is no strong correlation between ion-confining potential and the thermal-barrier depth. By installing a calibrated H/sub α/ emission diagnostic to measure the ionization current, we have quantified particle balance between the ionization source current and the four plasma current channels: (1) axial losses, (2) nonambipolar radial losses, (3) ambipolar radial losses, and (4) density changes. All current channels are directly measured except for the ambipolar current, which is inferred from the particle balance equation. TMX-U operation above 1 to 3 x 1012 cm-3 is dominated by current channel (1) and below 1 x 1012 cm-3 by one or more of the remaining three channels. Central-cell particle buildup has been observed for one or two e-foldings and, within the radial core, found consistent with particle balance