Scintillator based energetic ion loss diagnostic for the National Spherical Torus Experiment

Darrow, D. S.

doi:10.1063/1.2827514

Cited by 60 publications

(50 citation statements)

References 27 publications

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“…New insights into the interaction between fast particles and large scale magnetic perturbations have been gained by the deployment of a fast ion loss detector [5] following the principle design used on TFTR [40] and later W7-AS [41]. In addition to the observation with a CCD camera an array of photomultipliers, with a bandwidth of 1 MHz is used.…”

Section: Interaction Of Fast Particles With Magnetic Perturbationsmentioning

confidence: 99%

Interaction of energetic particles with large and small scale instabilities

Günter

Conway

Graca³

et al. 2007

Nucl. Fusion

124

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Beyond a certain heating power, measured and predicted distributions of NBI driven currents deviate from each other even in the absence of MHD instabilities. The most reasonable explanation is a redistribution of fast NBI ions on a time scale smaller than the current redistribution time. The hypothesis of a redistribution of fast ions by background turbulence is discussed. Direct numerical simulation of fast test particles in a given field of electrostatic turbulence indicates that for reasonable parameters fast and thermal particle diffusion can indeed be similar. -High quality plasma edge density profiles on ASDEX Upgrade and the recent extension of the reflectometry system allow for a direct comparison of observed TAE eigenfunctions with theoretical ones as obtained with the linear, gyrokinetic, global stability code LIGKA. These comparisons support the hypothesis of TAE-frequency crossing the continuum at the plasma edge in ASDEX Upgrade H-mode discharges. -A new fast ion loss detector with 1 MHz time resolution allows frequency and phase resolved correlation between the observed losses and low frequency magnetic perturbations such as TAE modes and rotating magnetic islands.Whereas losses caused by TAE modes are known to be due to resonances in velocity space, by modelling of the particle drift orbits we were able to explain losses caused by magnetic islands as due to island formation and stochasticity in the drift orbits.

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Section: Interaction Of Fast Particles With Magnetic Perturbationsmentioning

confidence: 99%

Interaction of energetic particles with large and small scale instabilities

Günter

Conway

Graca³

et al. 2007

Nucl. Fusion

124

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“…NSTX is equipped with a gyro radius and pitch angle dispersing scintillator-type fast ion loss diagnostic. [7] Interestingly, this diagnostic shows fast ion loss for some but not all avalanches. In addition, when losses are seen, the pitch angle range of the lost particles can vary substantially.…”

Section: Introductionmentioning

confidence: 99%

Stochastic orbit loss of neutral beam ions from NSTX due to toroidal Alfvén eigenmode avalanches

et al. 2012

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Abstract. Short toroidal Alfvén eigenmode (TAE) avalanche bursts in the National Spherical Torus Experiment (NSTX) cause a drop in the neutron rate and sometimes a loss of neutral beam ions at or near the full injection energy over an extended range of pitch angles. The simultaneous loss of wide ranges of pitch angle suggests stochastic transport of the beam ions occurs. When beam ion orbits are followed with a guiding center code that incorporates plasma's magnetic equilibrium plus the measured modes, the predicted ranges of lost pitch angle are similar to those seen in the experiment, with distinct populations of trapped and passing orbits lost. These correspond to domains where the stochasticity extends in the orbit phase space from the region of beam ion deposition to the loss boundary. IntroductionIn National Spherical Torus Experiment (NSTX)[1-3] plasmas, short (≤2 ms) bursts of toroidal Alfvén eigenmodes [4,5] are sometimes seen with multiple toroidal mode numbers, n, present simultaneously. These are termed TAE avalanches.[6] These avalanches are always accompanied by drops in the neutron rate of the order of 5 to 25 percent. Neutron production in NSTX results predominantly from reactions of the injected 90 keV deuterons with bulk plasma deuterons, which typically have a temperature in the range of 1-2 keV. Because the avalanches do not usually change the bulk plasma profiles appreciably, the drops in neutron rate have typically been attributed to neutral beam ion redistribution or loss. NSTX is equipped with a gyro radius and pitch angle dispersing scintillator-type fast ion loss diagnostic. [7] Interestingly, this diagnostic shows fast ion loss for some but not all avalanches. In addition, when losses are seen, the pitch angle range of the lost particles can vary substantially. In this work, we compare avalanches in two similar discharges in NSTX, one that evidences loss on the scintillator detector and one that does not. In concert with this, we apply recently a developed phase space mapping technique [8] that can identify which portions of the particle orbit phase space are stochastic given an equilibrium, mode structures, and mode amplitudes. This technique predicts little loss to the detector in the avalanche where no losses

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“…Such losses are diagnosed, for example, by Faraday cup [18] and scintillator Fast Loss Ion Probe (sFLIP) [19] diagnostics that detect ions on loss orbits. Resonant interaction of high-energy particles with magnetic perturbations in toroidal devices can produce large-scale modification of the particle distribution, sometimes leading to particle loss.…”

Section: Global and Compressional Alfvén Eigenmodes (Gae And Cae Resmentioning

confidence: 99%

Investigation Of A Transient Energetic Charge Exchange Fux Enhancement ('spike-on-tail') Observed In Neutral-beam-heated H-mode Discharges In The National Spherical Torus Experiment

Medley¹

2011

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In the National Spherical Torus Experiment (NSTX), a large increase in the charge exchange neutral flux localized at the Neutral Beam (NB) injection full energy is measured by the E||B (superimposed parallel electric and magnetic fields) Neutral Particle Analyzer (NPA). Termed the High-Energy Feature (HEF), it appears on the NB-injected energetic ion spectrum only in discharges where tearing or kink-type modes (f < 50 kHz) are absent, % in the measured neutron yield and total stored energy that are observed to coincide with the feature appear to be driven by concomitant broadening of measured Te(r), Ti(r) and n e (r) profiles and not the HEF itself. While the HEF has minimal impact on plasma performance, it nevertheless poses a challenging wave-particle interaction phenomenon to understand. Candidate mechanisms for HEF formation are developed based on quasilinear theory of wave-particle interaction. The only mechanism found to lead to the large NPA flux ratios, € H = F max /F min , observed in NSTX is the quasilinear evolution of the energetic ion distribution, , in phase space and the concomitant loss of some particles, which occurs due to the cyclotron interaction of the particles with destabilized modes having sufficiently high frequencies, kHz, in the plasma frame that are tentatively identified as Global Alfvén Eigenmodes.

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Scintillator based energetic ion loss diagnostic for the National Spherical Torus Experiment

Cited by 60 publications

References 27 publications

Interaction of energetic particles with large and small scale instabilities

Interaction of energetic particles with large and small scale instabilities

Stochastic orbit loss of neutral beam ions from NSTX due to toroidal Alfvén eigenmode avalanches

Investigation Of A Transient Energetic Charge Exchange Fux Enhancement ('spike-on-tail') Observed In Neutral-beam-heated H-mode Discharges In The National Spherical Torus Experiment

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