Wave driven fast ion loss in the National Spherical Torus Experiment

Fredrickson, E. D.; Cheng, C. Z.; Darrow, D.S.; Fu, G. Y.; Kramer, G. J.; Medley, S. S.; Ménard, J.; Roquemore, L.; Stutman, D.; White, R. B.

doi:10.1063/1.1579493

Cited by 75 publications

(76 citation statements)

References 57 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In NSTX beam heated plasmas we see transient neutron rate drops, correlated with bursts of fast ion driven instabilities, including modes identified as TAE and fishbone-like EPM. 26 The CAE and GAE may also affect fast ion confinement, but so far there is little direct evidence for the enhanced transport of fast ions in the presence of these instabilities.…”

Section: Physics Of Plasmas 13 056109 ͑2006͒mentioning

confidence: 99%

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

et al. 2006

Self Cite

View full text Add to dashboard Cite

A wide variety of fast ion driven instabilities are excited during neutral beam injection ͑NBI͒ in the National Spherical Torus Experiment ͑NSTX͒ ͓Nucl. Fusion 40, 557 ͑2000͔͒ due to the large ratio of fast ion velocity to Alfvén velocity, V fast / V Alfvén , and high fast ion beta. The ratio V fast / V Alfvén in ITER ͓Nucl. Fusion 39, 2137 ͑1999͔͒ and NSTX is comparable. The modes can be divided into three categories: chirping energetic particle modes ͑EPM͒ in the frequency range 0 to 120 kHz, the toroidal Alfvén eigenmodes ͑TAE͒ with a frequency range of 50 kHz to 200 kHz, and the compressional and global Alfvén eigenmodes ͑CAE and GAE, respectively͒ between 300 kHz and the ion cyclotron frequency. Fast ion driven modes are of particular interest because of their potential to cause substantial fast ion losses. In all regimes of NBI heated operation we see transient neutron rate drops, correlated with bursts of TAE or fishbone-like EPMs. The fast ion loss events are predominantly correlated with the EPMs, although losses are also seen with bursts of multiple, large amplitude TAE. The latter is of particular significance for ITER; the transport of fast ions from the expected resonance overlap in phase space of a "sea" of large amplitude TAE is the kind of physics expected in ITER. The internal structure and amplitude of the TAE and EPMs has been measured with quadrature reflectometry and soft x-ray cameras. The TAE bursts have internal amplitudes of ñ / n = 1% and toroidal mode numbers 2 Ͻ n Ͻ 7. The EPMs are core localized, kink-like modes similar to the fishbones in conventional aspect ratio tokamaks. Unlike the fishbones, the EPMs can be present with q͑0͒ Ͼ 1 and can have a toroidal mode number n Ͼ 1. The range of the frequency chirp can be quite large and the resonance can be through a fishbone-like precessional drift resonance, or through a bounce resonance.

show abstract

Section: Physics Of Plasmas 13 056109 ͑2006͒mentioning

confidence: 99%

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

et al. 2006

Self Cite

View full text Add to dashboard Cite

show abstract

“…Transport studies of energy, current, momentum, and particle confinement require accurate knowledge of the fast-ion profile. Since fast-ion driven instabilities occur in nearly every beam-heated NSTX discharge, 1 deviations from neoclassical fast-ion confinement are a virtual certainty. The HHFW system is another vital tool.…”

Section: Introductionmentioning

confidence: 99%

Fast-ion D-alpha diagnostic for NSTX

Heidbrink

Bell

Luo

et al. 2006

Review of Scientific Instruments

View full text Add to dashboard Cite

A fast-ion D-alpha ͑FIDA͒ diagnostic is under development for the National Spherical Torus Experiment ͑NSTX͒. The FIDA technique is a charge-exchange recombination spectroscopy measurement that exploits the large Doppler shift of Balmer-alpha light from energetic hydrogenic atoms to infer the fast-ion density. The principal objective of the NSTX installation is to measure the transport of beam ions caused by fast-ion driven instabilities; detection of perpendicular acceleration of fast ions during high harmonic fast wave heating is another important goal. Recent data from a DIII-D FIDA diagnostic guide the design. The planned NSTX diagnostic consists of two separate instruments focusing on different aspects of the measurement. One instrument uses a transmission grating spectrometer to measure the perpendicular energy spectrum and the spatial profile every 10 ms; the anticipated resolution is ϳ10 keV in energy and ϳ5 cm in radius. A second instrument employs bandpass filters to detect fast-ion redistribution events with millisecond temporal resolution.

show abstract

“…Fast ions are well known to excite a variety of MHD instabilities, and several types of fast-ion-induced modes have been observed on NSTX ranging in frequency from the Compressional Alfvén Eigenmode (CAE) [12,13] (f=0.5-2MHz) to the Toroidal Alfvén Eigenmode (TAE) (f=20-200kHz) and "bounce" and bounce-precession fishbones [14] (f < 100kHz). On the other hand, trapped energetic ions are also well known [15] to help stabilize the internal kink mode.…”

Section: Fast Particle Effectsmentioning

confidence: 99%

Internal Kink Mode Dynamics in High-beta NSTX Plasmas

Menard¹,

Bell²,

Fredrickson³

et al. 2004

View full text Add to dashboard Cite

Abstract.Saturated internal kink modes have been observed in many of the highest toroidal β discharges of the National Spherical Torus Experiment (NSTX). These modes often cause rotation flattening in the plasma core, can degrade energy confinement, and in some cases contribute to the complete loss of plasma angular momentum and stored energy. Characteristics of the modes are measured using soft X-ray, kinetic profile, and magnetic diagnostics. Toroidal flows approaching Alfvénic speeds, island pressure peaking, and enhanced viscous and diamagnetic effects associated with high-β may contribute to mode non-linear stabilization. These saturation mechanisms are investigated for NSTX parameters and compared to experimental data.

show abstract

Wave driven fast ion loss in the National Spherical Torus Experiment

Cited by 75 publications

References 57 publications

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

Fast-ion D-alpha diagnostic for NSTX

Internal Kink Mode Dynamics in High-beta NSTX Plasmas

Contact Info

Product

Resources

About