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Title: Two Photon Absorption Laser Induced Fluorescence for Neutral Hydrogen Profile Measurements

Abstract

The magnitude and spatial dependence of neutral density in magnetic confinement fusion experiments is a key physical parameter, particularly in the plasma edge. Modeling codes require precise measurements of the neutral density to calculate charge-exchange power losses and drag forces on rotating plasmas. However, direct measurements of the neutral density are problematic. In this work, we proposed to construct a laser-based diagnostic capable of providing spatially resolved measurements of the neutral density in the edge of plasma in the DIII-D tokamak. The diagnostic concept is based on two-photon absorption laser induced fluorescence (TALIF). By injecting two beams of 205 nm light (co or counter propagating), ground state hydrogen (or deuterium or tritium) can be excited from the n = 1 level to the n = 3 level at the location where the two beams intersect. Individually, the beams experience no absorption, and therefore have no difficulty penetrating even dense plasmas. After excitation, a fraction of the hydrogen atoms decay from the n = 3 level to the n = 2 level and emit photons at 656 nm (the Hα line). Calculations based on the results of previous TALIF experiments in magnetic fusion devices indicated that a laser pulse energy ofmore » approximately 3 mJ delivered in 5 ns would provide sufficient signal-to-noise for detection of the fluorescence. In collaboration with the DIII-D engineering staff and experts in plasma edge diagnostics for DIII-D from Oak Ridge National Laboratory (ORNL), WVU researchers designed a TALIF system capable of providing spatially resolved measurements of neutral deuterium densities in the DIII-D edge plasma. The laser systems were specified, purchased, and assembled at WVU. The TALIF system was tested on a low-power hydrogen discharge at WVU and the plan was to move the instrument to DIII-D for installation in collaboration with ORNL researchers. After budget cuts at DIII-D, the DIII-D facility declined to support installation on their tokamak. Instead, after a no-cost extension, the apparatus was moved to the University of Washington-Seattle and successfully tested on the HIT-SI3 spheromak experiment. As a result of this project, TALIF measurements of the absolutely calibrated neutral density hydrogen and deuterium were obtained in a helicon source and in a spheromak, designs were developed for installation of a TALIF system on a tokamak, and a new, xenon-based calibration scheme was proposed and demonstrated. The xenon-calibration scheme eliminates significant problems that were identified with the standard krypton calibration scheme.« less

Authors:
 [1]
  1. West Virginia Univ., Morgantown, WV (United States)
Publication Date:
Research Org.:
West Virginia Univ., Morgantown, WV (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
Contributing Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); General Atomics, San Diego, CA (United States)
OSTI Identifier:
1326021
Report Number(s):
DOE_WVU-SC0004736
3042920830; TRN: US1700288
DOE Contract Number:  
SC0004736
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; FLUORESCENCE; ROTATING PLASMA; SPHEROMAK DEVICES; HYDROGEN; PHOTONS; DENSITY; DEUTERIUM; ABSORPTION; XENON; LASER RADIATION; TRITIUM; HYDROGEN 1; FAR ULTRAVIOLET RADIATION; BEAMS; CALIBRATION; WASHINGTON; GROUND STATES; DESIGN; EXCITATION; SPACE DEPENDENCE; DE-EXCITATION; LYMAN LINES; PULSES; PLASMA DIAGNOSTICS; POWER RANGE 100-1000 KW; TOKAMAK DEVICES; HELICON WAVES; two photon laser induced fluorescence; neutral density measurements

Citation Formats

Scime, Earl E. Two Photon Absorption Laser Induced Fluorescence for Neutral Hydrogen Profile Measurements. United States: N. p., 2016. Web. doi:10.2172/1326021.
Scime, Earl E. Two Photon Absorption Laser Induced Fluorescence for Neutral Hydrogen Profile Measurements. United States. https://doi.org/10.2172/1326021
Scime, Earl E. 2016. "Two Photon Absorption Laser Induced Fluorescence for Neutral Hydrogen Profile Measurements". United States. https://doi.org/10.2172/1326021. https://www.osti.gov/servlets/purl/1326021.
@article{osti_1326021,
title = {Two Photon Absorption Laser Induced Fluorescence for Neutral Hydrogen Profile Measurements},
author = {Scime, Earl E.},
abstractNote = {The magnitude and spatial dependence of neutral density in magnetic confinement fusion experiments is a key physical parameter, particularly in the plasma edge. Modeling codes require precise measurements of the neutral density to calculate charge-exchange power losses and drag forces on rotating plasmas. However, direct measurements of the neutral density are problematic. In this work, we proposed to construct a laser-based diagnostic capable of providing spatially resolved measurements of the neutral density in the edge of plasma in the DIII-D tokamak. The diagnostic concept is based on two-photon absorption laser induced fluorescence (TALIF). By injecting two beams of 205 nm light (co or counter propagating), ground state hydrogen (or deuterium or tritium) can be excited from the n = 1 level to the n = 3 level at the location where the two beams intersect. Individually, the beams experience no absorption, and therefore have no difficulty penetrating even dense plasmas. After excitation, a fraction of the hydrogen atoms decay from the n = 3 level to the n = 2 level and emit photons at 656 nm (the Hα line). Calculations based on the results of previous TALIF experiments in magnetic fusion devices indicated that a laser pulse energy of approximately 3 mJ delivered in 5 ns would provide sufficient signal-to-noise for detection of the fluorescence. In collaboration with the DIII-D engineering staff and experts in plasma edge diagnostics for DIII-D from Oak Ridge National Laboratory (ORNL), WVU researchers designed a TALIF system capable of providing spatially resolved measurements of neutral deuterium densities in the DIII-D edge plasma. The laser systems were specified, purchased, and assembled at WVU. The TALIF system was tested on a low-power hydrogen discharge at WVU and the plan was to move the instrument to DIII-D for installation in collaboration with ORNL researchers. After budget cuts at DIII-D, the DIII-D facility declined to support installation on their tokamak. Instead, after a no-cost extension, the apparatus was moved to the University of Washington-Seattle and successfully tested on the HIT-SI3 spheromak experiment. As a result of this project, TALIF measurements of the absolutely calibrated neutral density hydrogen and deuterium were obtained in a helicon source and in a spheromak, designs were developed for installation of a TALIF system on a tokamak, and a new, xenon-based calibration scheme was proposed and demonstrated. The xenon-calibration scheme eliminates significant problems that were identified with the standard krypton calibration scheme.},
doi = {10.2172/1326021},
url = {https://www.osti.gov/biblio/1326021}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Sep 23 00:00:00 EDT 2016},
month = {Fri Sep 23 00:00:00 EDT 2016}
}

Works referenced in this record:

Novel xenon calibration scheme for two-photon absorption laser induced fluorescence of hydrogen
journal, July 2016


Two-photon LIF on the HIT-SI3 experiment: Absolute density and temperature measurements of deuterium neutrals
journal, July 2016


Two photon absorption laser induced fluorescence measurements of neutral density in a helicon plasma
journal, May 2014


Neutral depletion and the helicon density limit
journal, December 2013


Direct measurements of the ionization profile in krypton helicon plasmas
journal, December 2012


A two photon absorption laser induced fluorescence diagnostic for fusion plasmas
journal, October 2012