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New capabilities and results for the National Spherical Torus Experiment

M.G. Bell, R.E. Bell, D.A. Gates, S.M. Kaye, H. Kugel, B.P. LeBlanc, F.M. Levinton1, R. Maingi2, J.E. Menard, R. Raman3, S.A. Sabbagh4, D. Stutman5 and the NSTX Research Team

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The National Spherical Torus Experiment (NSTX) produces plasmas with toroidal aspect ratio as low as 1.25, which can be heated by up to 6 MW high-harmonic fast waves and up to 7 MW of deuterium neutral beam injection. Using new poloidal field coils, plasmas with cross-section elongation up to 2.7, triangularity 0.8, plasma currents Ip up to 1.5 MA and normalized currents Ip/aBT up to 7.5 MA/mcenterdotT have been achieved. A significant extension of the plasma pulse length, to 1.5 s at a plasma current of 0.7 MA, has been achieved by exploiting the bootstrap and NBI-driven currents to reduce the dissipation of poloidal flux. Inductive plasma startup has been supplemented by coaxial helicity injection (CHI) and the production of persistent current on closed flux surfaces by CHI has now been demonstrated in NSTX. The plasma response to magnetic field perturbations with toroidal mode numbers n = 1 or 3 and the effects on the plasma rotation have been investigated using three pairs of coils outside the vacuum vessel. Recent studies of both MHD stability and of transport benefitted from improved diagnostics, including measurements of the internal poloidal field using the motional Stark effect (MSE). In plasmas with a region of reversed magnetic shear in the core, now confirmed by the MSE data, improved electron confinement has been observed.


 
aSee appendix for members of the NSTX Research Team.
PACS

52.25.Fi Transport properties

52.55.Hc Stellarators, torsatrons, heliacs, bumpy tori, and other toroidal confinement devices

52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

52.55.Wq Current drive; helicity injection

52.55.Tn Ideal and resistive MHD modes; kinetic modes

52.70.Gw Radio-frequency and microwave measurements

Subjects

Instrumentation and measurement

Plasma physics

Dates

Issue 8 (August 2006)

Received 24 January 2006, accepted for publication 5 April 2006

Published 17 July 2006



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