Skip to main content
construction release_alert
The Scholars Team is working with OIT to resolve some issues with the Scholars search index
cancel
Journal cover image

Investigation of a transient energetic charge exchange flux enhancement ('spike-on-tail') observed in neutral-beam-heated H-mode discharges in the National Spherical Torus Experiment

Publication ,  Journal Article
Medley, SS; Kolesnichenko, YI; Yakovenko, YV; Bell, RE; Bortolon, A; Crocker, NA; Darrow, DS; Diallo, A; Domier, CW; Fonck, RJ; Fredrickson, ED ...
Published in: Nuclear Fusion
January 1, 2012

In the National Spherical Torus Experiment (NSTX), a large increase in the charge exchange neutral flux localized around the neutral beam (NB) injection full energy is measured using a neutral particle analyser. 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, toroidal Alfvén eigenmode activity (f ∼ 50-150 kHz) is weak and global Alfvén eigenmode (GAE) activity (f ∼ 400-1000 kHz) is robust. Compressional Alfvén eigenmode activity (f > 1000 kHz) is usually sporadic or absent during the HEF event. The HEF exhibits growth times of Δt ∼ 20-80 ms, durations spanning 100-600 ms and peak-to-base flux ratios up to H = F max/F min ∼ 10. In infrequent cases, a slowing-down distribution below the HEF energy can develop that continues to evolve over periods of order 100 ms, a time scale long compared with the typical fast-ion equilibration times. HEFs are observed only in H-mode (not L-mode) discharges with injected power P b ≥ 4 MW and in the pitch range χ ≡ v ||/v ∼ 0.7-0.9; i.e. only for passing particles. Increases of order 10-30% 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 T e(r), T i(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 (QL) 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 QL evolution of the energetic-ion distribution, F b(E, χ, r), in phase space. A concomitant loss of some particles is observed due to interaction through cyclotron resonance of the particles with destabilized modes having sufficiently high frequencies, f ∼ 700-1000 kHz, in the plasma frame that are tentatively identified as GAEs. © 2012 IAEA, Vienna.

Duke Scholars

Published In

Nuclear Fusion

DOI

EISSN

1741-4326

ISSN

0029-5515

Publication Date

January 1, 2012

Volume

52

Issue

1

Related Subject Headings

  • Fluids & Plasmas
  • 5106 Nuclear and plasma physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
 

Citation

APA
Chicago
ICMJE
MLA
NLM
Medley, S. S., Kolesnichenko, Y. I., Yakovenko, Y. V., Bell, R. E., Bortolon, A., Crocker, N. A., … White, R. B. (2012). Investigation of a transient energetic charge exchange flux enhancement ('spike-on-tail') observed in neutral-beam-heated H-mode discharges in the National Spherical Torus Experiment. Nuclear Fusion, 52(1). https://doi.org/10.1088/0029-5515/52/1/013014
Medley, S. S., Y. I. Kolesnichenko, Y. V. Yakovenko, R. E. Bell, A. Bortolon, N. A. Crocker, D. S. Darrow, et al. “Investigation of a transient energetic charge exchange flux enhancement ('spike-on-tail') observed in neutral-beam-heated H-mode discharges in the National Spherical Torus Experiment.” Nuclear Fusion 52, no. 1 (January 1, 2012). https://doi.org/10.1088/0029-5515/52/1/013014.
Medley SS, Kolesnichenko YI, Yakovenko YV, Bell RE, Bortolon A, Crocker NA, Darrow DS, Diallo A, Domier CW, Fonck RJ, Fredrickson ED, Gerhardt SP, Gorelenkov NN, Kramer GJ, Kubota S, Leblanc BP, Lee KC, Mazzucato E, McKee GR, Podestà M, Ren Y, Roquemore AL, Smith DR, Stutman D, Tritz K, White RB. Investigation of a transient energetic charge exchange flux enhancement ('spike-on-tail') observed in neutral-beam-heated H-mode discharges in the National Spherical Torus Experiment. Nuclear Fusion. 2012 Jan 1;52(1).
Journal cover image

Published In

Nuclear Fusion

DOI

EISSN

1741-4326

ISSN

0029-5515

Publication Date

January 1, 2012

Volume

52

Issue

1

Related Subject Headings

  • Fluids & Plasmas
  • 5106 Nuclear and plasma physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics