Plasma shape control on the National Spherical Torus Experiment (NSTX) using real-time equilibrium reconstruction

Gates, D.; Ferron, J. R.; Bell, M.G.; Gibney, T.; Johnson, Robert D.; Marsala, R.; Mastrovito, D.; Ménard, J.; Mueller, D.; Penaflor, B.G.; Sabbagh, S. A.; Stevenson, T.

doi:10.1088/0029-5515/46/1/002

Cited by 67 publications

(58 citation statements)

References 12 publications

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“…PPPU2 and PPPL2 are names of axisymmetric poloidal flux loops, whose flux and voltage signals are used to assess and control the plasma vertical position and velocity [47]. The chords labelled USXR (ultra-soft x-ray) and Bol.…”

Section: Experimental Backgroundmentioning

confidence: 99%

“…The plasma shape in NSTX is controlled through the combined rtEFIT and isoflux algorithms [52] implemented in the General Atomics Plasma Control System (PCS) [53], originally developed for DIII-D and then implemented on NSTX [47]. Both dr sep and z maxis are available as independent requestable parameters in the shape control algorithm.…”

Section: Development Of Jogging Techniquesmentioning

confidence: 99%

“…There is also a fast vertical position control loop in series with the shape controller [47]. This controller drives a PF-3 current asymmetry that is proportional to the difference in voltages on the flux loops labelled PPPU2 and PPPL2 in figure 1 [47] (the voltages are in turn roughly proportional to the plasma vertical velocity).…”

Section: Development Of Jogging Techniquesmentioning

confidence: 99%

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First observation of ELM pacing with vertical jogs in a spherical torus

et al. 2010

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Experiments in a number of conventional aspect ratio tokamaks have been successful in pacing edge localized modes (ELMs) by rapid vertical jogging of the plasma. This paper demonstrates the first pacing of ELMs in a spherical torus plasma. Applied 30 Hz vertical jogs synchronized the ELMs with the upward motion of the plasma. 45 Hz jogs also lead to an increase in the ELM frequency, though the synchronization of the ELMs and jogs was unclear. A reduction in the ELM energy was observed at the higher driven ELM frequencies.

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Section: Experimental Backgroundmentioning

confidence: 99%

Section: Development Of Jogging Techniquesmentioning

confidence: 99%

Section: Development Of Jogging Techniquesmentioning

confidence: 99%

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First observation of ELM pacing with vertical jogs in a spherical torus

et al. 2010

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“…The value of l i is determined by the current drive sources and thermal profiles, and the calculations in Fig. 18 indicate that peaked thermal profiles may result in l i too high for stable vertical position control with the present control system [146]. Improvements to the vertical control system have since been implemented, and will be tested in the early phase of NSTX-Upgrade operations.…”

mentioning

confidence: 96%

Exploration of the equilibrium operating space for NSTX-Upgrade

Gerhardt¹,

André²,

Ménard³

2012

Nucl. Fusion

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This paper explores a range of high-performance equilibrium scenarios achievable with neutral beam heating in the NSTX-Upgrade device (Menard J.E. 2012 Nucl. Fusion 52 083015). NSTX-Upgrade is a substantial upgrade to the existing NSTX device (Ono M. et al 2000 Nucl. Fusion 40 557), with significantly higher toroidal field and solenoid capabilities, and three additional neutral beam sources with significantly larger current-drive efficiency. Equilibria are computed with free-boundary TRANSP, allowing a self-consistent calculation of the non-inductive current-drive sources, the plasma equilibrium and poloidal-field coil currents, using the realistic device geometry. The thermal profiles are taken from a variety of existing NSTX discharges, and different assumptions for the thermal confinement scalings are utilized. The no-wall and ideal-wall n = 1 stability limits are computed with the DCON code. The central and minimum safety factors are quite sensitive to many parameters: they generally increase with large outer plasma-wall gaps and higher density, but can have either trend with the confinement enhancement factor. In scenarios with strong central beam current drive, the inclusion of non-classical fast-ion diffusion raises qmin, decreases the pressure peaking, and generally improves the global stability, at the expense of a reduction in the non-inductive current-drive fraction; cases with less beam current drive are largely insensitive to additional fast-ion diffusion. The non-inductive current level is quite sensitive to the underlying confinement and profile assumptions. For instance, for BT = 1.0 T and Pinj = 12.6 MW, the non-inductive current level varies from 875 kA with ITER-98y,2 thermal confinement scaling and narrow thermal profiles to 1325 kA for an ST specific scaling expression and broad profiles. Scenarios are presented which can be sustained for 8–10 s, or (20–30) τCR, at βN = 3.8–4.5. The value of qmin can be controlled at either fixed non-inductive fraction of 100% or fixed plasma current, by varying which beam sources are used, opening the possibility for feedback control of the current profile. In terms of quantities like collisionality, neutron emission, non-inductive fraction, or stored energy, these scenarios represent a significant performance extension compared with NSTX and other present spherical torii.

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“…1. Note that the shape control in NSTX is provided by a combination of realtime equilibrium reconstruction and plasma boundary control with an "ISOFLUX" algorithm [77]. Also, dynamic error field correction (DEFC) of n=1 error fields [78], static correction of n=3 error fields [79] and fast RWM control [80,81] are important for improving the overall stability and reliability of these discharge scenarios.…”

mentioning

confidence: 99%