Session BO4: NSTX and Spherical Torus
9:30 AM–12:30 PM, Monday, November 14, 2011
Room: Ballroom E
Chair: Ted Biewer, Oak Ridge National Laboratory
Abstract ID: BAPS.2011.DPP.BO4.14
Abstract: BO4.00014 : Recent Results from the Pegasus Toroidal Experiment
12:06 PM–12:18 PM
Preview Abstract
MathJax On | Off 
Abstract 
Authors:
A.J. Redd
J.L. Barr
M.W. Bongard
M.G. Burke
R.J. Fonck
E.T. Hinson
D.J. Schlossberg
N.L. Schoenbeck
K.E. Thome
(Univ of Wisc - Madison)
Pegasus is an ultra-low aspect ratio spherical tokamak (A=1.15), used to study the physics of low-A plasmas and develop non-solenoidal tokamak startup techniques. A combination of point-source magnetic helicity injection and poloidal field induction produces non-solenoidal tokamak plasmas with $I_p \le 0.17$ MA using $~4$ kA injected current $I_{inj}$, consistent with the heilicity injection rate and a Taylor relaxation limit. A strong double layer sheath at the injectors describes the impedance of the injection circuit, implying the helicity injection rate for a given $I_{inj}$ is a strong function of the local plasma density. Impurity ion spectroscopy indicates strong heating ($T_i$ $\sim$ 0.5 keV) during helicity drive. Passive gas-fueled electrodes can be used as helicity injectors, complementing active current sources and affording a means to optimize the Taylor and helicity injection limits. Ohmic plasmas in Pegasus are often unstable to peeling modes, an instability underlying edge localized modes (ELMs) in larger tokamaks. Time-resolved current profile measurements show that ELM-like, current-carrying filaments form at the plasma edge, which then detach and propagate outward.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.BO4.14