Operational Limits in the National Spherical Torus Experiment
Authors: S.M. Kaye, M.G. Bell, R.E. Bell, D. Gates, R. Maingi, E. Mazzucato, J. Menard, D. Mueller, W. Park, S. Paul, S. Sabbagh, and D. Stutman
Date of PPPL Report: June 2000
Presented at: the 27th European Physical Society's (EPS) Conference on Controlled Fusion and Plasma Physics, June 12-16, 2000, Budapest, Hungary. A "Provisional Collection of Submitted Contributions" can be found at the following web site: http://www.eps2000.kfki.hu (active as of August 16, 2000). Papers are in PDF format.
The National Spherical Torus Experiment (NSTX) is a proof-of-principle scale device whose mission is to establish the physics basis of low aspect configurations most notably in the areas of plasma stability, transport and non-inductive current drive [1,2]. The first series of physics experiments was conducted during the period from Sept. 1999 through Jan. 2000 [3-7]. Among the first experiments was a study to map out and characterize the operational density and q-limits. Density limits have typically been associated with enhanced radiated power due to overfuelling or impurity influx [8], although ion neoclassical transport may impose a density limit at very high densities in ohmic, gas-fueled plasmas [9]. q-limits have typically been manifestations of destabilization of m=2/n=1 kink or tearing modes that lead to a sudden discharge termination [8].