#
55th Annual Meeting of the APS Division of Plasma Physics

## Volume 58, Number 16

##
Monday–Friday, November 11–15, 2013;
Denver, Colorado

### Session CP8: Poster Session II: Astro, Simulations, RFP, Tokamak, Stellarator

Monday, November 11, 2013

Room: Plaza ABC

Abstract ID: BAPS.2013.DPP.CP8.87

### Abstract: CP8.00087 : Magnetic Relaxation with Oscillating Field Current Drive on MST

Preview Abstract
Abstract

####
Authors:

D.R. Stone

(UW Madison)

A.F. Almagri

(UW Madison)

K.J. McCollam

(UW Madison)

J.S. Sarff

(UW Madison)

In oscillating field current drive (OFCD) poloidal and toroidal ac magnetic
fields are inductively applied to the plasma to drive dc plasma current
through magnetic relaxation. In OFCD experiments on the MST RFP up to 10{\%}
additional current is added. Measurements of Ohm's Law terms including the
dynamo mechanisms associated with magnetic relaxation are conducted during
OFCD to better understand the relaxation dynamics and to possibly aid in
optimizing OFCD performance. The fluctuation-induced dynamo ${\left\langle
{\tilde{{E}}\cdot \tilde{{B}}} \right\rangle } \mathord{\left/ {\vphantom
{{\left\langle {\tilde{{E}}\cdot \tilde{{B}}} \right\rangle } B}} \right.
\kern-\nulldelimiterspace} B\cong {\left\langle {\tilde{{V}}\times
\tilde{{B}}} \right\rangle -\left\langle {\tilde{{J}}\times \tilde{{B}}}
\right\rangle } \mathord{\left/ {\vphantom {{\left\langle {\tilde{{V}}\times
\tilde{{B}}} \right\rangle -\left\langle {\tilde{{J}}\times \tilde{{B}}}
\right\rangle } {ne}}} \right. \kern-\nulldelimiterspace} {ne}$ and its
constituent Hall dynamo ${\left\langle {\tilde{{J}}\times \tilde{{B}}}
\right\rangle } \mathord{\left/ {\vphantom {{\left\langle {\tilde{{J}}\times
\tilde{{B}}} \right\rangle } {ne}}} \right. \kern-\nulldelimiterspace} {ne}$
are measured in the edge ($r \mathord{\left/ {\vphantom {r {a=.9}}} \right.
\kern-\nulldelimiterspace} {a=.9})$ using inserted probes, and compared to
$\eta J-E$. A passive secondary-emission capacitive probe was developed to
measure the electric field fluctuations (accurate when the plasma
temperature \textgreater 20 eV). Ohm's Law balance is observed during OFCD.
During sawtooth relaxation events with OFCD the edge dynamo is enhanced
compared to events without OFCD. Between events the edge dynamo is a few V/m
and opposes the edge current. This opposing dynamo is required to balance
Ohm's Law during OFCD since the oscillating electric field adds excess
current at the plasma edge and the dynamo tends to flatten the current
profile. Supported by the US DOE and the NSF.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2013.DPP.CP8.87