Non-inductive solenoid-free plasma start-up using coaxial helicity injection

Raman, R.; Jarboe, T. R.; O'Neill, R.G.; Hamp, W. T.; Nelson, B. A.; Izzo, V.A.; Redd, A. J.; Sieck, P.E.; Smith, Roger

doi:10.1088/0029-5515/45/4/l01

Cited by 22 publications

(17 citation statements)

References 12 publications

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“…A discharge to achieve this goal can be divided into three phases; the breakdown and startup with Coaxial Helicity Injection (CHI) or the outer poloidal field coils (described elsewhere [18,19]), the early plasma current rampup and heating with High Harmonic Fast Waves (HHFW), and the later plasma current rampup and heating from both HHFW and NBI. The first phase is not modeled here and will not be discussed further in this study.…”

Section: Simulations Of Non-solenoidal Current Rampupmentioning

confidence: 99%

Long pulse high performance plasma scenario development for the National Spherical Torus Experiment

Kessel

Bell

et al. 2006

Physics of Plasmas

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Abstract.The National Spherical Torus Experiment (NSTX) [Ono, M., et al., Nucl. Fusion, 44, (2004), 452.] is targeting long pulse high performance, non-inductive sustained operations at low aspect ratio, and the demonstration of non-solenoidal startup and current rampup. The modeling of these plasmas provides a framework for experimental planning and identifies the tools to access these regimes. Simulations based on NBI (Neutral Beam Injection)-heated plasmas are made to understand the impact of various modifications and identify the requirements for 1) high elongation and triangularity, 2) density control to optimize the current drive, 3) plasma rotation and/or feedback stabilization to operate above the no-wall β limit, and 4) Electron Bernstein Waves (EBW) for off-axis heating/current drive (H/CD). Integrated scenarios are constructed to provide the transport evolution and H/CD source modeling, supported by rf and stability analyses. Important factors include the energy confinement, Z eff , early heating/H-mode, broadening of the NBI-driven current profile, and maintaining q(0) and q min >1.0. Simulations show that non-inductive sustained plasmas can be reached at I P =800 kA, B T =0.5 T, κ≈2.5, β N ≤5, β≤15%, f NI =92%, and q(0)>1.0 with NBI H/CD, density control, and similar global energy confinement to experiments. The non-inductive sustained high β plasmas can be reached at I P =1.0 MA, B T =0.35 T, κ≈2.5, β N ≤9, β≤43%, f NI =100%, and q(0)>1.5 with NBI H/CD and 3.0 2 MW of EBW H/CD, density control, and 25% higher global energy confinement than experiments. A scenario for non-solenoidal plasma current rampup is developed using High Harmonic Fast Wave (HHFW) H/CD in the early low I P and low T e phase, followed by NBI H/CD to continue the current ramp, reaching a maximum of 480 kA after 3.4 s.

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Section: Simulations Of Non-solenoidal Current Rampupmentioning

confidence: 99%

Long pulse high performance plasma scenario development for the National Spherical Torus Experiment

Kessel

Bell

et al. 2006

Physics of Plasmas

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“…This current can be reduced by minimizing the poloidal fields in the region near the absorber gap or by reducing the size of the capacitor bank used to form the discharge so that the capacitor bank is mostly depleted of energy by the time the CHI discharge has filled the vessel. CHI discharges produced on HIT-II have also been shown to couple to induction and to outperform inductive-only plasmas [6]. Similar coupling studies on NSTX as well as optimization to reduce the extent of absorber arc current are the subject of future NSTX experiments.…”

Section: Resultsmentioning

confidence: 89%

“…After this time the CHI circuit is no longer being actively driven. Thus the only plausible explanation for any persisting current past this time must be due to decaying closed flux equilibrium [6]. Figure 3a shows that about 75 kA of closed flux current is generated in these discharges in HIT-II and that about 30 kA of injector current is needed.…”

Section: Resultsmentioning

confidence: 98%

“…On HIT-II [6] and on NSTX [7], CHI is implemented by driving current along externally produced field lines that connect coaxial electrodes mounted on the electrically isolated inner and outer vacuum vessel components in the presence of externally generated toroidal and poloidal magnetic fields. Figures 1 and 2 are the layout of the HIT-II and NSTX experiments.…”

Section: Introductionmentioning

confidence: 99%

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Plasma Start-up in HIT-II and NSTX Using Transient Coaxial Helicity Injection

et al. 2007

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“…This new method referred to as transient CHI has been highly successful on the HIT-II experiment. 11 On the HIT-II experiment, transient CHI has been used to successfully couple a CHI started discharge to induction. The method is simple and highly reproducible and has allowed HIT-II consistently to produce higher current discharges than what was possible by induction alone.…”

Section: Introductionmentioning

confidence: 99%

Transient coaxial helicity injection for solenoid-free plasma startup in HIT-II

et al. 2007

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The favorable properties of the spherical torus ͑ST͒ arise from its very small aspect ratio. Methods for initiating the plasma current without relying on induction from a central solenoid are essential for the viability of the ST concept. In steady state tokamaks, the central solenoid can be dispensed with if suitable methods for initiating the plasma current are on hand. Coaxial helicity injection ͑CHI͒ is a promising candidate for solenoid-free plasma current startup in STs and tokamaks. Experiments on the Helicity Injected Torus ͑HIT-II͒ machine at the University of Washington ͓T. R. Jarboe, Fusion Technol. 15, 7 ͑1989͔͒ have demonstrated the capability of a new method, referred to as transient CHI, to produce a high quality closed-flux equilibrium that has been successfully coupled to induction demonstrating that this new plasma current startup method is compatible with the conventional inductive method. This paper presents physics requirements for implementing this method in STs and tokamaks and supporting experimental results from the HIT-II device.

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Non-inductive solenoid-free plasma start-up using coaxial helicity injection

Cited by 22 publications

References 12 publications

Long pulse high performance plasma scenario development for the National Spherical Torus Experiment

Long pulse high performance plasma scenario development for the National Spherical Torus Experiment

Plasma Start-up in HIT-II and NSTX Using Transient Coaxial Helicity Injection

Transient coaxial helicity injection for solenoid-free plasma startup in HIT-II

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