### Session TP8: Poster Session VII: Reconnection and Non-Neutral II; High Power Microwave and Laser Driven Sources; NSTX Spherical / General Torus; Simulation: HEDP/Plasma Accelerator/Space

9:30 AM–9:30 AM, Thursday, November 15, 2007
Rosen Centre Hotel Room: Grand Ballroom, 9:30am - 12:30pm

Abstract ID: BAPS.2007.DPP.TP8.109

### Abstract: TP8.00109 : Operations at High I$_{N}$ in the Pegasus Toroidal Experiment

Preview Abstract MathJax On | Off   Abstract

#### Authors:

E.A. Unterberg
D.J. Battaglia
M.W. Bongard
M.J. Frost
G.D. Garstka
A.C. Sontag
In efforts to define the operating space of a near-unity aspect ratio ST, the external kink boundary is explored by operating at high normalized current (I$_{N})$ and toroidal field utilization (I$_{P}$/I$_{TF})$. Recent experiments have accessed I$_{N}$ up to 14 MA/m-T (I$_{P}$/I$_{TF} \quad \sim$ 2.3) through current profile manipulation. Three techniques are employed to access high I$_{N}$. The first two involve electrostatic current sources for helicity injection, while the third uses TF rampdowns. Equilibrium reconstructions indicate that two techniques are allowing dramatic changes in the current profile and the third is accessing high I$_{N}$ through greater experimental flexibility. Mode analysis during the current manipulation experiments shows no consistent mode activity. The MHD activity that is observed appears to coincide with reduced shear at rational flux surfaces destabilizing tearing modes at higher m. This is opposed to earlier experiments with ohmic-only current drive where low-order tearing modes were universally observed, limiting I$_{N}$ ($\sim$ 6-8 MA/m-T) and I$_{P}$/I$_{TF}$ to unity. There has yet to be evidence of ideal MHD mode activity during these experiments giving encouragement than further gains in I$_{N}$ can be made.