Abstract Details

Add files

Characterizing the unique current and density profiles of the Resistive Wall Machine

Author: David A Hannum
Requested Type: Consider for Invited
Submitted: 2010-01-20 16:29:59

Co-authors: W. Bergerson, M. Brookhart, C.B. Forest, R. Kendrick, C. Paz-Soldan

Contact Info:
UW-Madison
1150 University Ave
Madison, WI   53715
USA

Abstract Text:
The Resistive Wall Machine is a line-tied screw pinch at UW-Madison built to study stabilization of the Resistive Wall Mode (RWM) using moving walls. It uses an array of electrostatic guns which can be individually fired to create plasma and separately biased to drive current. The RWM has been identified and characterized using a variety of shells with different wall times. A variety of wall materials have been used to study other modes, such as quartz (for the unmodified kink mode) and an iron-nickel alloy (for the Ferritic Wall Mode). Recent work with a 2D probe traverse has focused on measuring radial and axial profiles of $n_e$, $T_e$, $varphi$, and $J_z$ to gauge the applicability of ideal MHD to the experiment, and also to analyze the novel plasma source. The modular gun design has opened up studies of current and density profile control. Direct measurement of $n_e$ and $J_z$ down the column show that particle density scales strongly with the plasma current. Discrete current and density filaments merge (due in part to magnetic shear phase mixing) to give a nearly uniform, cylindrically symmetric column within 30 cm of the plasma guns. Measurement of $varphi$ shows that the core of the plasma rotates strongly ($v_theta approx$ 12 km/sec) at the start of the column, slowing down to 2 km/sec at the end. The overall picture is a cool, dense plasma better described by resistive MHD than ideal, with $tau_{rm diff} < tau_{rm wall}$. Characterization of the screw pinch's plasma and modes sets the stage for RWM stabilization with rotating walls, due to begin this spring.

Characterization: A3,A5

Comments: