Progress towards Steady State on NSTX

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In order to reduce recirculating power fraction to acceptable levels, the spherical torus concept relies on the simultaneous achievement of high toroidal {beta} and high bootstrap fraction in steady state. In the last year, as a result of plasma control system improvements, the achievable plasma elongation on the National Spherical Torus Experiment (NSTX) has been raised from {kappa} {approx} 2.1 to {kappa} {approx} 2.6--approximately a 25% increase. This increase in elongation has lead to a doubling increase in the toroidal {beta} for long-pulse discharges. The increase in {beta} is associated with an increase in plasma current at nearly fixed poloidal ... continued below

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Gates, D.A.; Kessel, C.; Menard, J.; Taylor, G.; Wilson, J.R. & co-authors, plus 94 January 24, 2005.

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In order to reduce recirculating power fraction to acceptable levels, the spherical torus concept relies on the simultaneous achievement of high toroidal {beta} and high bootstrap fraction in steady state. In the last year, as a result of plasma control system improvements, the achievable plasma elongation on the National Spherical Torus Experiment (NSTX) has been raised from {kappa} {approx} 2.1 to {kappa} {approx} 2.6--approximately a 25% increase. This increase in elongation has lead to a doubling increase in the toroidal {beta} for long-pulse discharges. The increase in {beta} is associated with an increase in plasma current at nearly fixed poloidal {beta}, which enables higher {beta}{sub t} with nearly constant bootstrap fraction. As a result, for the first time in a spherical torus, a discharge with a plasma current of 1 MA has been sustained for 1 second. Data is presented from NSTX correlating the increase in performance with increased plasma shaping capability. In addition to improved shaping, H-modes induced during the current ramp phase of the plasma discharge have been used to reduce flux consumption during and to delay the onset of MHD instabilities. A modeled integrated scenario, which has 100% non-inductive current drive with very high toroidal {beta}, will also be presented. The NSTX poloidal field coils are currently being modified to produce the plasma shape which is required for this scenario, which requires high triangularity ({delta} {approx} 0.8) at elevated elongation ({kappa} {approx} 2.5). The other main requirement for steady state on NSTX is the ability to drive a fraction of the total plasma current with radio-frequency waves. The results of High Harmonic Fast Wave heating and current drive studies as well as electron Bernstein Wave emission studies will be presented.

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INIS; OSTI as DE00836619

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  • Other Information: Supercedes report DE00836619; PBD: 24 Jan 2005

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  • Report No.: PPPL-4044
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/836619 | External Link
  • Office of Scientific & Technical Information Report Number: 836619
  • Archival Resource Key: ark:/67531/metadc781225

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  • January 24, 2005

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  • Dec. 3, 2015, 9:30 a.m.

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  • June 10, 2016, 6:11 p.m.

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Gates, D.A.; Kessel, C.; Menard, J.; Taylor, G.; Wilson, J.R. & co-authors, plus 94. Progress towards Steady State on NSTX, report, January 24, 2005; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc781225/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.