Non-inductive current generation in NSTX using coaxial helicity injection

Raman, R.; Jarboe, T. R.; Mueller, D.; Schaffer, M. J.; Maqueda, R. J.; Nelson, B.A.; Sabbagh, S. A.; Bell, M.G.; Ewig, R.; Fredrickson, E. D.; Gates, D.; Hosea, J.; Jardin, S.C.; Ji, Hantao; Kaita, R.; Kaye, S. M.; Kugel, H.; Lao, L. L.; Maingi, R.; Ménard, J.; Ono, M.; Orvis, D. J.; Paoletti, F.; Paul, S. F.; Peng, Yi; Skinner, C.H.; Wilgen, J. B.; Zweben, S. J.

doi:10.1088/0029-5515/41/8/311

Cited by 73 publications

(40 citation statements)

References 15 publications

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“…Oxygen levels after boronization remained low, unless there was a change in type of plasma operations (neutral beam injection, CHI [16], minor vent). Boronization has been repeated 5 times between intervals of 2-3 weeks.…”

Section: Plasma Behaviormentioning

confidence: 98%

Effect of boronization on ohmic plasmas in NSTX

et al. 2002

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Abstract:Boronization of the National Spherical Torus Experiment (NSTX) has enabled access to higher density, higher confinement plasmas. A glow discharge with 4 mTorr helium and 10% deuterated trimethyl boron deposited 1.7 g of boron on the plasma facing surfaces. Ion beam analysis of witness coupons showed a B+C areal density of 10 18 (B+C) cm -2 corresponding to a film thickness of 100 nm. Subsequent ohmic discharges showed oxygen emission lines reduced by x15, carbon emission reduced by two and copper reduced to undetectable levels. After boronization, the plasma current flattop time increased by 70% enabling access to higher density, higher confinement plasmas.

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Section: Plasma Behaviormentioning

confidence: 98%

Effect of boronization on ohmic plasmas in NSTX

et al. 2002

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“…Figure 1 shows the layout of the NSTX device, which contains the location of the poloidal field coils, divertor and passive plates, relevant to the discussion in this paper. The device is fueled using gas injection from piezo valves at four different locations on the machine, from a fifth location at the mid-plane of the center stack and, during CHI operations 2 , from the lower divertor plate region. Understanding the edge neutral pressure changes on a fast timescale and at different locations on the vessel during various modes of plasma operations is necessary for establishing pumping and fueling requirements and eventually for controlling the edge neutral pressures at the desired level.…”

Section: Introductionmentioning

confidence: 99%

Fast Neutral Pressure Measurements in NSTX

Raman¹,

Kugel²,

Provost³

et al. 2002

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Several fast neutral pressure gauges have been installed on NSTX to measure the vessel and divertor pressure during inductive and coaxial helicity injected (CHI) plasma operations. Modified, PDX-type Penning gauges have been installed on the upper and lower divertors. Neutral pressure measurements during plasma operations from these and from two shielded fast Micro ion gauges at different toroidal locations on the vessel mid-plane are described. A new unshielded ion gauge, referred to as the In-vessel Neutral Pressure (INP) gauge is under development.

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“…CHI is implemented on NSTX by driving current along field lines that connect the inner and outer lower divertor plates. A description of the CHI system on NSTX can be found in Reference [33].A 50kA, 1k V DC power supply is connected across the inner and outer vessel components, which are insulated from each other by ceramic rings at the bottom and top. The CHI method drives current initially on open field lines, creating a current density profile that is hollow and intrinsically unstable.…”

Section: Coaxial Helicity Injectionmentioning

confidence: 99%

The National Spherical Torus Experiment (NSTX) Research Program and Progress Towards High Beta, Long Pulse Operating Scenarios

Synakowski¹,

Bell²,

Bell³

et al. 2002

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-A major research goal of the National Spherical Torus Experiment is establishing long-pulse, high beta, high confinement operation and its physics basis. This research has been enabled by facility capabilities developed over the last two years, including neutral beam (up to 7 MW) and high harmonic fast wave heating (up to 6 MW), toroidal fields up to 6 kG, plasma currents up to 1.5 MA, flexible shape control, and wall preparation techniques. These capabilities have enabled the generation of plasmas with <β T > up to 35%. Normalized beta values often exceed the no wall limit, and studies suggest that passive wall mode stabilization is enabling this for broad pressure profiles characteristic of H mode plasmas. The viability of long, high bootstrap current fraction operations has been established for ELMing H mode plasmas with toroidal beta values in excess of 15% and sustained for several current relaxation times. Improvements in wall conditioning and fueling are likely contributing to a reduction in H mode power thresholds. Electron thermal conduction is the dominant thermal loss channel in auxiliary heated plasmas examined thus far. HHFW effectively heats electrons, and its acceleration of fast beam ions has been observed. Evidence for HHFW current drive is by comparing of the loop voltage evolution in plasmas with matched density and temperature profiles but varying phases of launched HHFW waves. A peak heat flux of 10 MW/m 2 has been measured in the H mode, with large asymmetries in the power deposition being observed between the inner and outer strike points. Noninductive plasma startup studies have focused on coaxial helicity injection. With this technique, toroidal currents up to 400 kA have been driven, and studies to assess flux closure and coupling to other current drive techniques have begun.

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Non-inductive current generation in NSTX using coaxial helicity injection

Cited by 73 publications

References 15 publications

Effect of boronization on ohmic plasmas in NSTX

Effect of boronization on ohmic plasmas in NSTX

Fast Neutral Pressure Measurements in NSTX

The National Spherical Torus Experiment (NSTX) Research Program and Progress Towards High Beta, Long Pulse Operating Scenarios

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