skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Experimentally-based ExB drifts in the DIII-D divertor and SOL calculated from integration of Ohm's law using Thomson scattering measurements of T e and n e

Abstract

We calculated the 2D spatial distributions of cross field drift velocities from 2D Thomson scattering measurements of T e and n e in the divertor and SOL of DIII-D. In contrast with the method that has been used on DIII-D where the 2D distribution of plasma potential V plasma is obtained from measurements of the probe floating potential of reciprocating probes, the present method does not require insertion of a probe into the plasma and can therefore be used in high power discharges. Furthermore, the 2D spatial distribution of V plasma is calculated from Ohm’s Law for the parallel electric field E || along each flux tube, E || s || = -1.71dT e/ds || - T e/n edn e/ds ||, where the Thomson scattering values of T e and n e are used. To within a constant of integration, V plasma is obtained by integrating E || along the flux-tubes (field lines); the constant is obtained for each flux tube using the sheath drop at the target calculated from the characteristic of Langmuir probes built into the divertor tiles. The 2D distributions of E./01/2 = -dV4/ds./01/2, E452510/2 = -dV4/ds452510/2, v789 452510/2 = E./01/2/B and v789 ./01/2 = E452510/2/B aremore » then calculated as well as the particle drift flux densities Γ789 452510/2 = nv789 452510/2 and Γ789 ./01/2 = nv789 ./01/2 for electrons, fuel ions and impurity ions, using the appropriate values of particle density, n.« less

Authors:
 [1];  [1];  [2];  [3]
  1. University of Toronto Inst. for Aerospace Studies, Toronto, ON (Canada)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1375000
Grant/Contract Number:
FC02-04ER54698; AC52-07NA27344; AC04-94AL8500
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Materials and Energy
Additional Journal Information:
Journal Volume: 12; Journal ID: ISSN 2352-1791
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DIII-D; divertor; drifts; Thomson scattering

Citation Formats

Stangeby, Peter C., Elder, J. David, McLean, Adam G., and Watkins, Jonathan G.. Experimentally-based ExB drifts in the DIII-D divertor and SOL calculated from integration of Ohm's law using Thomson scattering measurements of Te and ne. United States: N. p., 2017. Web. doi:10.1016/j.nme.2017.03.021.
Stangeby, Peter C., Elder, J. David, McLean, Adam G., & Watkins, Jonathan G.. Experimentally-based ExB drifts in the DIII-D divertor and SOL calculated from integration of Ohm's law using Thomson scattering measurements of Te and ne. United States. doi:10.1016/j.nme.2017.03.021.
Stangeby, Peter C., Elder, J. David, McLean, Adam G., and Watkins, Jonathan G.. Mon . "Experimentally-based ExB drifts in the DIII-D divertor and SOL calculated from integration of Ohm's law using Thomson scattering measurements of Te and ne". United States. doi:10.1016/j.nme.2017.03.021. https://www.osti.gov/servlets/purl/1375000.
@article{osti_1375000,
title = {Experimentally-based ExB drifts in the DIII-D divertor and SOL calculated from integration of Ohm's law using Thomson scattering measurements of Te and ne},
author = {Stangeby, Peter C. and Elder, J. David and McLean, Adam G. and Watkins, Jonathan G.},
abstractNote = {We calculated the 2D spatial distributions of cross field drift velocities from 2D Thomson scattering measurements of Te and ne in the divertor and SOL of DIII-D. In contrast with the method that has been used on DIII-D where the 2D distribution of plasma potential Vplasma is obtained from measurements of the probe floating potential of reciprocating probes, the present method does not require insertion of a probe into the plasma and can therefore be used in high power discharges. Furthermore, the 2D spatial distribution of Vplasma is calculated from Ohm’s Law for the parallel electric field E|| along each flux tube, E|| s|| = -1.71dTe/ds|| - Te/nedne/ds||, where the Thomson scattering values of Te and ne are used. To within a constant of integration, Vplasma is obtained by integrating E|| along the flux-tubes (field lines); the constant is obtained for each flux tube using the sheath drop at the target calculated from the characteristic of Langmuir probes built into the divertor tiles. The 2D distributions of E./01/2 = -dV4/ds./01/2, E452510/2 = -dV4/ds452510/2, v789 452510/2 = E./01/2/B and v789 ./01/2 = E452510/2/B are then calculated as well as the particle drift flux densities Γ789 452510/2 = nv789 452510/2 and Γ789 ./01/2 = nv789 ./01/2 for electrons, fuel ions and impurity ions, using the appropriate values of particle density, n.},
doi = {10.1016/j.nme.2017.03.021},
journal = {Nuclear Materials and Energy},
number = ,
volume = 12,
place = {United States},
year = {Mon Mar 27 00:00:00 EDT 2017},
month = {Mon Mar 27 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • This paper describes divertor density and temperature measurements using both a new reciprocating Langmuir probe (XPT-RCP) which plunges vertically above the divertor floor up to the X-point height and swept, single, Langmuir probes fixed horizontally across the divertor floor. These types of measurements are important for testing models of the SOL and divertor which then are used to design plasma facing components in reactor size tokamaks. This paper presents an overview of the new divertor probe measurements and how they compare with the new divertor Thomson scattering system. The fast time response of the probe measurements allows detailed study ofmore » ELMs.« less
  • A modeling study is reported using new 2D data from DIII-D tokamak divertor plasmas and improved 2D transport model that includes large cross-field drifts for the numerically difficult H-mode regime. The data set, which spans a range of plasmas densities for both forward and reverse toroidal magnetic field (B t) over a range of plasma densities, is provided by divertor Thomson scattering (DTS). Measurements utilizing X-point sweeping give corresponding 2D profiles of electron temperature (T e) and density (n e) across both divertor legs for individual discharges. The calculations show the same features of in/out plasma asymmetries as measured inmore » the experiment, with the normal B t direction (ion ∇B drift toward the X-point) having higher n e and lower T e in the inner divertor leg than outer. Corresponding emission data for total radiated power shows a strong inner-divertor/outer-divertor asymmetry that is reproduced by the simulations. Furthermore, these 2D UEDGE transport simulations are enabled for steep-gradient H-mode conditions by newly implemented algorithms to control isolated grid-scale irregularities.« less
  • The first Thomson scattering measurements of n{sub e} and T{sub e} in the divertor region of a tokamak are reported. These data are used as input to boundary physics codes such as UEDGE and DEGAS and to benchmark the predictive capabilities of these codes. These measurements have also contributed to the characterization of tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through the lower divertor region of the DIII{endash}D tokamak. A custom, aspherical collection lens ({ital f}/6.8) images the laser beam from 1 to 21 cm above the target plates into eightmore » spatial channels with 1.5 cm vertical and 0.3 cm radial resolution. Two-dimensional mapping of the divertor region is achieved by sweeping the divertor {ital X}-point location radically through the fixed laser beam location. Fiber optics carry the light to polychromators whose interference filters have been optimized for low-T{sub e} measurements. Silicon avalanche photodiodes measure both the scattered and plasma background light. Temperatures and densities are typically in the range of 5{endash}200 eV and 1{endash}10{times}10{sup 19} m{sup {minus}3}, respectively. Low temperatures, T{sub e}{lt}1 eV, and high densities, n{sub e}{gt}8{times}10{sup 8} cm{sup {minus}3} have been observed in detached plasmas. Background light levels have not been a significant problem. Reduction of the laser stray light permits Rayleigh calibration. Because of access difficulties, no in-vessel vacuum alignment target could be used. Instead, an {ital in situ} laser alignment monitor provides alignment information for each laser pulse. Results are compared with Langmuir probe measurements where good agreement is found except for regions of high n{sub e} and low T{sub e} as measured by Thomson scattering. {copyright} {ital 1997 American Institute of Physics.}« less
  • Thomson scattering measurements of {ital n{sub e}} and {ital T{sub e}} in the divertor region of a Tokamak are reported. These data are used as input to boundary physics codes such as UEDGE and DEGAS and to benchmark the predictive capabilities of these codes. These measurements have also contributed to the characterization of tokamak disruptions. A Nd:YAG laser (20 Hz, 1 J, 15 ns, 1064 nm) is directed vertically through the lower divertor region of the DIII{endash}D Tokamak. A custom, aspherical collection lens {ital (f/6.8)} images the laser beam from 1 to 21 cm above the target plates into eightmore » spatial channels with 1.5 cm vertical and 0.3 cm radial resolution. Two-dimensional mapping of the divertor region is achieved by sweeping the divertor {ital X}-point location radially through the fixed laser beam location. Fiber optics carry the light to polychromators whose interference filters have been optimized for low {ital T{sub e}} measurements. Silicon avalanche photodiodes measure both the scattered and plasma background light. Temperatures and densities are typically in the range of 5{endash}200 eV and 1{endash}10{times}10{sup 19} m{sup {minus}3}, respectively. Low temperatures, {ital T{sub e}{lt}1} eV, and high densities, {ital n{sub e}}{gt}8{times}10{sup 20} m{sup {minus}3} have been observed in detached plasmas. Background light levels have not been a significant problem. Reduction of the laser stray light permits Rayleigh calibration. Because of access difficulties, no in-vessel vacuum alignment target could be used. Instead, an {ital in situ} laser alignment monitor provides alignment information for each laser pulse. Results are compared with Langmuir probe measurements where good agreement is found except for regions of high {ital n{sub e}} and low {ital T{sub e}} as measured by Thomson scattering. {copyright} {ital 1997 American Institute of Physics.}« less
  • Local measurements of [ital n][sub [ital e]] and [ital T][sub [ital e]] in the divertor region are necessary for a more complete understanding of divertor physics. We have designed an extension to the existing multipulse Thomson scattering system [Carlstrom [ital et] [ital al]., Rev. Sci. Instrum. [bold 63], 4901 (1992)] to measure [ital n][sub [ital e]] in the range 5[times]10[sup 18]--5[times]10[sup 20] m[sup [minus]3] and [ital T][sub [ital e]] in the range 5--500 eV with 1 cm resolution from 1 to 21 cm above the floor of the DIII-D vessel (eight spatial channels) in the region of the [ital X]more » point for lower single-null diverted plasmas. One of the existing, 20 Hz, Nd:YAG lasers will be redirected to a separate vertical port and viewed radially with a specially designed [ital f]/6.8 lens. Fiber optics carry the light to polychromators whose interference filters have been optimized for low [ital T][sub [ital e]] measurements. Other aspects of the system, including the beam path to the vessel, polychromator design, real-time data acquisition, laser control, calibration facility, and DIII-D timing and data acquisition interface, will be shared with the existing multipulse Thomson system. An [ital in] [ital situ] laser alignment monitor will provide alignment information for each laser pulse.« less