Efficient generation of noninductive, off-axis, Ohkawa current, driven by electron Bernstein waves in high β, spherical torus plasmas

Taylor, G.; Efthimion, P. C.; Kessel, C. E.; Harvey, R. W.; Смирнов, А. П.; Ershov, N. M.; Carter, M. D.; Forest, C. B.

doi:10.1063/1.1792635

Cited by 47 publications

(41 citation statements)

References 18 publications

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“…The current drive arises from the Ohkawa effect [17], rather than the conventional Fisch-Boozer effect, and therefore is driven opposite to the direction of the launched waves. The large trapped particle fraction on the low field side of the plasma at low aspect ratio leads to the high current drive efficiency The heating and CD deposition results from GENRAY/CQL3D are used in the simulations, and further details can be found for NSTX in ref [9].…”

Section: Simulations Of 100% Non-inductive Sustained High β Plasmmentioning

confidence: 99%

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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 100% Non-inductive Sustained High β Plasmmentioning

confidence: 99%

“…It is used here to examine High Harmonic Fast Wave anisotropy. The GENRAY and CQL3D [8,9] codes are used to establish the Electron Bernstein Wave (EBW) deposition and current drive. GENRAY is a ray-tracing calculation based on the Stix hot plasma, non-relativisitic dispersion relation.…”

Section: Computational Approachmentioning

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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“…After the plasma becomes overdense for ECRH, the plasma current will be ramped up by bootstrap current and direct current drive using high-harmonic fast-wave heating and neutral beam injection. Earlier modeling of a high β, 100% non-inductive plasma scenario in NSTX [6] during the plasma current flat top showed that off-axis EBW current drive [7] can help to stabilize the plasma equilibrium. An upgrade of the 1 MW 28 GHz ECRH system to a 2 MW electron Bernstein wave (EBW) heating and current drive system is being considered for later implementation on NSTX-U.…”

Section: Introductionmentioning

confidence: 99%

ECRH/EBWH system for NSTX-U

Taylor

Ellis

Harvey

et al. 2012

EPJ Web of Conferences

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Abstract. The National Spherical Torus Experiment Upgrade (NSTX-U) will operate at an axial toroidal field of up to 1 T, about twice the field available on NSTX. A 28 GHz electron cylotron resonance heating (ECRH) system is currently being planned for NSTX-U. A 1 MW 28 GHz gyrotron will be employed. Intially the system will use short, 10-50 ms, 1 MW pulses for ECRH-assisted discharge start-up. Later the pulse length will be extended to 1-5 s to study electron Bernstein wave heating (EBWH) during the plasma current flat top. A mirror launcher will be used to couple microwave power to the plasma via O-mode to the slow X-mode to EBW (O-X-B) double mode conversion. This paper presents a pre-conceptual design for the ECRH/EBWH system proposed for NSTX-U and includes ray tracing and Fokker-Planck modeling results for 28 GHz ECRH during plasma start-up and EBW heating and current drive during the plasma current flattop of a NSTX-U advanced H-mode plasma scenario.

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“…EBWs are particularly suitable for heating and current drive in the high-β plasmas of spherical tori like the National Spherical Torus Experiment (NSTX) [5] and the Mega Amp Spherical Tokamak (MAST) [6], where ω p ω c over most of the plasma. There have been a number of theoretical works on the EBW dispersion relation [7] [8] [9], on mode conversion to EBWs [10] [11] [12], on emission of EBWs [13], and on current drive by EBWs [14]. However, a detailed study of the characteristics of EBWs and their resonant interaction with electrons has been lacking.…”

Section: Introductionmentioning

confidence: 99%

Relativistic description of electron Bernstein waves

Decker

Ram

2006

Physics of Plasmas

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The application of the extraordinary and ordinary electron cyclotron waves for heating and current drive in overdense, magnetized plasmas is restricted. For frequencies near low harmonics of the electron cyclotron frequency these waves are cutoff near the edge of the plasma. For higher frequencies the interaction of the waves with electrons is weak leading to very low absorption of wave power. However, electron Bernstein waves provide means for heating and current drive in overdense plasmas since they have no density cutoffs and are strongly damped near harmonics of the electron cyclotron resonance. This paper discusses properties of electron Bernstein waves that make them an attractive means for delivering energy and momentum to electrons. An approximate analytical model for electrostatic waves in the weakly relativistic and weak damping limits is developed. From this model the propagation and damping characteristics of electron Bernstein waves and their dependence on plasma parameters are derived. It is found that relativistic effects are necessary to properly describe the resonant interaction of electron Bernstein waves with electrons. The characteristics of electron Bernstein wave propagation and damping are very different depending on whether the electron cyclotron harmonic resonance is approached from the low-or the high-field side. The results from the analytical model and the associated analysis agree well with the results from the exact numerical calculations. This validates the physics of the simplifying assumptions on which the model is based. The electron Bernstein waves are completely damped well before the electron cyclotron resonance due to the Doppler shift. Within the damping region the waves interact with suprathermal electrons thereby having the potential for efficient current drive.

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Efficient generation of noninductive, off-axis, Ohkawa current, driven by electron Bernstein waves in high β, spherical torus plasmas

Cited by 47 publications

References 18 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

ECRH/EBWH system for NSTX-U

Relativistic description of electron Bernstein waves

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