Initial Experiments at High Normalized Current in the Pegasus Toroidal Experiment

Unterberg, E.A.; Battaglia, D. J.; Fonck, R. J.; Eidietis, N. W.; Fonck, R. J.; Frost, Matthew; Garstka, G. D.; Kujak-Ford, B.A.; Lewicki, B.T.; Squires, B.; Winz, G.R.

doi:10.1007/s10894-006-9056-z

Cited by 4 publications

(3 citation statements)

References 5 publications

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“…As such, a complete model of the process is complex and not yet available. Initial numerical simulations of LHI with the NIMROD code [13][14][15] indicate that reconnection of the injected current streams leads to the large-scale field reversal, flux amplification, and buildup of toroidal current observed in experiment [3][4][5][7][8][9]. The simulations also show that hollow current profiles and closed flux surfaces exist during helicity injection in a toroidally-averaged sense, despite the presence of stochasticity.…”

Section: Introductionmentioning

confidence: 91%

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A power-balance model for local helicity injection startup in a spherical tokamak

Barr¹,

Fonck²,

Burke³

et al. 2018

Nucl. Fusion

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A 0D circuit model for predicting in Local Helicity Injection (LHI) discharges is developed. Analytic formulas for estimating the surface flux of finite- plasmas developed by Hirshman and Neilson (1986 Phys. Fluids 29 790) are modified and expanded to treat highly shaped, ultralow- tokamak geometry using a database of representative equilibria. Model predictions are compared to sample LHI discharges in the Pegasus spherical tokamak, and are found to agree within 15% of experimental . High performance LHI discharges are found to follow the Taylor relaxation current limit for approximately the first half of the current ramp, or 75 kA. The second half of the current ramp follows a limit imposed by power-balance as plasmas expand from high-A to ultralow-A. This shape evolution generates a significant drop in external plasma inductance, effectively using the plasma’s initially high inductance to drive the current ramp and provide >70% of the current drive V-s. Projections using this model indicate the relative influences of higher helicity input rate and injector current on the attainable total plasma current.

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Section: Introductionmentioning

confidence: 91%

“…Multiple alternate startup techniques are under active investigation [1][2][3][4][5][6][7][8][9]. In particular, the local helicity injection (LHI) technique is being developed on the Pegasus Toroidal Experiment [3][4][5][6][7][8][9]. LHI uses localized arc-sources to inject strong electron current along a helical background field.…”

Section: Introductionmentioning

confidence: 99%

A power-balance model for local helicity injection startup in a spherical tokamak

Barr¹,

Fonck²,

Burke³

et al. 2018

Nucl. Fusion

View full text Add to dashboard Cite

show abstract

“…It is a mid-sized spherical tokamak with 0. [9]. At the attained during operation at this low in a relatively small experiment, the electron collisionality is usually higher than desired for fusion applications.…”

mentioning

confidence: 97%

Noninductively Driven Tokamak Plasmas at Near-Unity Toroidal Beta

et al. 2017

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Access to and characterization of sustained, toroidally confined plasmas with a very high plasma-to-magnetic pressure ratio (β_{t}), low internal inductance, high elongation, and nonsolenoidal current drive is a central goal of present tokamak plasma research. Stable access to this desirable parameter space is demonstrated in plasmas with ultralow aspect ratio and high elongation. Local helicity injection provides nonsolenoidal sustainment, low internal inductance, and ion heating. Equilibrium analyses indicate β_{t} up to ∼100% with a minimum |B| well spanning up to ∼50% of the plasma volume.

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Attainment of High Normalized Current by Current Profile Manipulation in the Pegasus Toroidal Experiment

et al. 2007

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Initial Experiments at High Normalized Current in the Pegasus Toroidal Experiment

Cited by 4 publications

References 5 publications

A power-balance model for local helicity injection startup in a spherical tokamak

A power-balance model for local helicity injection startup in a spherical tokamak

Noninductively Driven Tokamak Plasmas at Near-Unity Toroidal Beta

Attainment of High Normalized Current by Current Profile Manipulation in the Pegasus Toroidal Experiment

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