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Title: Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak

Abstract

Spectra of passive fast-ion D-alpha (FIDA) light from beam ions that charge exchange with background neutrals are measured and simulated. The fast ions come from three sources: ions that pass through the diagnostic sightlines on their first full orbit, an axisymmetric confined population, and ions that are expelled into the edge region by instabilities. A passive FIDA simulation (P-FIDASIM) is developed as a forward model for the spectra of the first-orbit fast ions and consists of an experimentally-validated beam deposition model, an ion orbit-following code, a collisional-radiative model, and a synthetic spectrometer. Model validation consists of the simulation of 86 experimental spectra that are obtained using 6 different neutral beam fast-ion sources and 13 different lines of sight. Calibrated spectra are used to estimate the neutral density throughout the cross-section of the tokamak. The resulting 2D neutral density shows the expected increase toward each X-point with average neutral densities of 8 X 10 9 cm -3 at the plasma boundary and 1 X 10 11 cm -3 near the wall. Here, fast ions that are on passing orbits are expelled by the sawtooth instability more readily than trapped ions. In a sample discharge, approximately 1% of the fast-ion population ismore » ejected into the high neutral density region per sawtooth crash.« less

Authors:
 [1];  [1];  [2];  [2];  [2]
  1. Univ. of California, Irvine, CA (United States)
  2. General Atomics, San Diego, CA (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE), Nuclear Facility Operations (NE-3)
OSTI Identifier:
1371906
Grant/Contract Number:
FC02-04ER54698; FG03-94ER54271
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 11; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; passive FIDA; edge light; neutral density; FIDASIM; FIDA; sawtooth crash; fast ion losses

Citation Formats

Bolte, Nathan G., Heidbrink, William W., Pace, David, Van Zeeland, Michael, and Chen, Xi. Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak. United States: N. p., 2016. Web. doi:10.1088/0029-5515/56/11/112023.
Bolte, Nathan G., Heidbrink, William W., Pace, David, Van Zeeland, Michael, & Chen, Xi. Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak. United States. doi:10.1088/0029-5515/56/11/112023.
Bolte, Nathan G., Heidbrink, William W., Pace, David, Van Zeeland, Michael, and Chen, Xi. 2016. "Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak". United States. doi:10.1088/0029-5515/56/11/112023. https://www.osti.gov/servlets/purl/1371906.
@article{osti_1371906,
title = {Measurement and simulation of passive fast-ion D-alpha emission from the DIII-D tokamak},
author = {Bolte, Nathan G. and Heidbrink, William W. and Pace, David and Van Zeeland, Michael and Chen, Xi},
abstractNote = {Spectra of passive fast-ion D-alpha (FIDA) light from beam ions that charge exchange with background neutrals are measured and simulated. The fast ions come from three sources: ions that pass through the diagnostic sightlines on their first full orbit, an axisymmetric confined population, and ions that are expelled into the edge region by instabilities. A passive FIDA simulation (P-FIDASIM) is developed as a forward model for the spectra of the first-orbit fast ions and consists of an experimentally-validated beam deposition model, an ion orbit-following code, a collisional-radiative model, and a synthetic spectrometer. Model validation consists of the simulation of 86 experimental spectra that are obtained using 6 different neutral beam fast-ion sources and 13 different lines of sight. Calibrated spectra are used to estimate the neutral density throughout the cross-section of the tokamak. The resulting 2D neutral density shows the expected increase toward each X-point with average neutral densities of 8 X 109 cm-3 at the plasma boundary and 1 X 1011 cm-3 near the wall. Here, fast ions that are on passing orbits are expelled by the sawtooth instability more readily than trapped ions. In a sample discharge, approximately 1% of the fast-ion population is ejected into the high neutral density region per sawtooth crash.},
doi = {10.1088/0029-5515/56/11/112023},
journal = {Nuclear Fusion},
number = 11,
volume = 56,
place = {United States},
year = 2016,
month = 9
}

Journal Article:
Free Publicly Available Full Text
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  • Spectra of passive fast-ion D-alpha (FIDA) light from beam ions that charge exchange with background neutrals are measured and simulated. The fast ions come from three sources: ions that pass through the diagnostic sightlines on their first full orbit, an axisymmetric confined population, and ions that are expelled into the edge region by instabilities. A passive FIDA simulation (P-FIDASIM) is developed as a forward model for the spectra of the first-orbit fast ions and consists of an experimentally-validated beam deposition model, an ion orbit-following code, a collisional-radiative model, and a synthetic spectrometer. Model validation consists of the simulation of 86more » experimental spectra that are obtained using 6 different neutral beam fast-ion sources and 13 different lines of sight. Calibrated spectra are used to estimate the neutral density throughout the cross-section of the tokamak. The resulting 2D neutral density shows the expected increase toward each X-point with average neutral densities of 8 X 10 9 cm -3 at the plasma boundary and 1 X 10 11 cm -3 near the wall. Here, fast ions that are on passing orbits are expelled by the sawtooth instability more readily than trapped ions. In a sample discharge, approximately 1% of the fast-ion population is ejected into the high neutral density region per sawtooth crash.« less
  • Fast ions are produced by neutral beam injection and ion cyclotron heating in toroidal magnetic fusion devices. As deuterium fast ions orbit around the device and pass through a neutral beam, some deuterons neutralize and emit D{sub {alpha}} light. For a favorable viewing geometry, the emission is Doppler shifted away from other bright interfering signals. In the 2005 campaign, we built a two channel charge-coupled device based diagnostic to measure the fast-ion velocity distribution and spatial profile under a wide variety of operating conditions. Fast-ion data are acquired with a time resolution of {approx}1 ms, spatial resolution of {approx}5 cm,more » and energy resolution of {approx}10 keV. Background subtraction and fitting techniques eliminate various contaminants in the spectrum. Neutral particle and neutron diagnostics corroborate the D{sub {alpha}} measurement. Examples of fast-ion slowing down and pitch angle scattering in quiescent plasma and fast-ion acceleration by high harmonic ion cyclotron heating are presented.« less
  • The plasma of a tokamak with a vertically elongated cross section is normally kept in its central position by the action of a feedback system that controls currents in external coils. If this control becomes unsuccessful, a vertical displacement episode develops. During such an episode, the vacuum vessel may be subject to large vertical forces. Since these forces are large enough to impact the design of future devices, there is a need to understand them. In this paper a comparison is described between data from such vertical displacement episodes observed in the DIII-D tokamak (Bull. Am. Phys. Soc. {bold 31},more » 1533 (1986)) to those from a numerical simulation code designed to realize a previously suggested conceptual model for the plasma physics part of a displacement episode. The comparison suggests validity of the model and that the code provides a realization of the model. Other code runs suggest that before reasonable predictions can be made on vertical forces in future devices, specific scenarios for the time development of the currents of external coils during an episode are needed.« less