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Title: Spectroscopic Characterization and Simulation of Chemical Sputtering Using the DiMES Porous Plug Injector in DIII-D

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
940516
Report Number(s):
UCRL-JRNL-229165
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Nuclear Materials, vol. 363-365, N/A, June 15, 2007, pp. 86-90
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 29 ENERGY PLANNING, POLICY AND ECONOMY; 70 PLASMA PHYSICS AND FUSION

Citation Formats

McLean, A G, Davis, J W, Stangeby, P C, Brooks, N H, Whyte, D G, Allen, S L, Bray, B D, Brezinsek, S, Elder, J D, Fenstermacher, M E, Groth, M, Haasz, A A, Hollmann, E M, Isler, R C, Lasnier, C J, Rudakov, D L, Watkins, J G, West, W P, and Wong, C C. Spectroscopic Characterization and Simulation of Chemical Sputtering Using the DiMES Porous Plug Injector in DIII-D. United States: N. p., 2007. Web. doi:10.1016/j.jnucmat.2006.12.062.
McLean, A G, Davis, J W, Stangeby, P C, Brooks, N H, Whyte, D G, Allen, S L, Bray, B D, Brezinsek, S, Elder, J D, Fenstermacher, M E, Groth, M, Haasz, A A, Hollmann, E M, Isler, R C, Lasnier, C J, Rudakov, D L, Watkins, J G, West, W P, & Wong, C C. Spectroscopic Characterization and Simulation of Chemical Sputtering Using the DiMES Porous Plug Injector in DIII-D. United States. doi:10.1016/j.jnucmat.2006.12.062.
McLean, A G, Davis, J W, Stangeby, P C, Brooks, N H, Whyte, D G, Allen, S L, Bray, B D, Brezinsek, S, Elder, J D, Fenstermacher, M E, Groth, M, Haasz, A A, Hollmann, E M, Isler, R C, Lasnier, C J, Rudakov, D L, Watkins, J G, West, W P, and Wong, C C. Wed . "Spectroscopic Characterization and Simulation of Chemical Sputtering Using the DiMES Porous Plug Injector in DIII-D". United States. doi:10.1016/j.jnucmat.2006.12.062. https://www.osti.gov/servlets/purl/940516.
@article{osti_940516,
title = {Spectroscopic Characterization and Simulation of Chemical Sputtering Using the DiMES Porous Plug Injector in DIII-D},
author = {McLean, A G and Davis, J W and Stangeby, P C and Brooks, N H and Whyte, D G and Allen, S L and Bray, B D and Brezinsek, S and Elder, J D and Fenstermacher, M E and Groth, M and Haasz, A A and Hollmann, E M and Isler, R C and Lasnier, C J and Rudakov, D L and Watkins, J G and West, W P and Wong, C C},
abstractNote = {},
doi = {10.1016/j.jnucmat.2006.12.062},
journal = {Journal of Nuclear Materials, vol. 363-365, N/A, June 15, 2007, pp. 86-90},
number = ,
volume = ,
place = {United States},
year = {Wed Mar 14 00:00:00 EDT 2007},
month = {Wed Mar 14 00:00:00 EDT 2007}
}
  • A self-contained gas injection system for the Divertor Material Evaluation System (DiMES) on DIII-D has been employed for in-situ study of chemical erosion in the tokamak divertor environment. The Porous Plug Injector (PPI) releases methane, a major component of molecular influx due to chemical sputtering of graphite, from the tile surface into the plasma at a controlled rate through a porous graphite surface. Perturbation to local plasma is minimized, while also simulating the immediate environment of methane molecules released from a solid graphite surface. The release rate was chosen to be of the same order of magnitude as natural sputtering.more » Photon efficiencies of CH{sub 4} for measured local plasma conditions are reported. The contribution of chemical versus physical sputtering to the source of C{sup +} at the target is assessed through measurement of CII and CD/CH band emissions during release of CH{sub 4} from the PPI, and due to intrinsic emission.« less
  • An improved, self-contained gas injection system for the divertor material evaluation system (DIMES) on DIII-D has been employed for in situ study of chemical erosion in the tokamak divertor environment. To minimize perturbation to local plasma, the Mark II porous plug injector (PPI) releases methane through a porous graphite surface at the outer strike point at a rate precisely controlled by a micro-orifice flow restrictor to be approximately equal as that predicted for intrinsic chemical sputtering. Effective photon efficiencies resulting from CH(4) are found to be 58 +/- 12 in an attached divertor (n(e) similar to 1.5 x 10(13)/cm(3), T(e)more » similar to 25 eV, T(surf)similar to 450 K), and 94 +/- 20 in a semi-detached cold divertor (n(e) similar to 6.0 x 10(13)/cm(3), T(e) similar to 2-3 eV, T(surf) similar to 350 K). These values are significantly more than previous measurements in similar plasma conditions, indicating the importance of the injection rate and local re-erosion for the integrity of this analysis. The contribution of chemical versus physical sputtering to the source of C(+) at the target is assessed through simultaneous measurement of CII line, and CD plus CH-band emissions during release of CH(4) from the Pill, then compared with that seen in intrinsic sputtering. (C) 2009 Elsevier B.V. All rights reserved.« less
  • A Porous Plug Injector (PPI) system for the Divertor Material Evaluation System (DIMES) on DIII-D has been employed for in situ study of chemical erosion in the tokamak divertor environment. The 3D-DIVIMP(HC) code has been applied to the interpretation of the CI, CII and other spectroscopic measurements made at the PPI location, for (a) the synthetic source due to injection of CH4 through the PPI, and (b) the natural emission from the PPI head itself, which was inserted above surrounding graphite tiles by similar to 0.3 mm. The code successfully replicated the MDS (spectrometer)-measured absolute emissions of CH, CI, CIImore » 427 nm, 514 nm, and 658 nm [1] and the DiMES TV-measured spatial shapes of the CH, CI, and CII 514 nm [1] emission ''clouds'' to within the combined uncertainties. It is thus concluded that the most important physics and chemistry of chemical sputtering have most likely been included in the model.« less
  • A set of 19 dome-shaped divertor Langmuir probes similar in design to probes used in JET and JT-60 has been used successfully in DIII-D to measure the divertor electron temperature, particle flux, and floating potential. A comparison of the power flux using IR cameras with the particle flux and electron temperature from the probes using collisionless sheath theory has indicated that the particle flux to the divertor surface may be strongly modified by collisions within the magnetic sheath. In order to study this effect, a set of probes have been designed that can be inserted into the divertor plasma usingmore » DIMES. Two dome-shaped probes compare fluxes intercepted both above and within the magnetic sheath of the divertor surface. In addition, a third probe oriented normal to the magnetic field is used to verify the projected area of the probe surface. The probe design accommodates parallel power fluxes up to 50 MW/m[sup 2] for 30 ms, allowing for the study of beam-heated plasmas in DIII-D.« less
  • Here, tungsten button samples were exposed to He ELMing H-mode plasma in DIII-D using 2.3 MW of electron cyclotron heating power. Prior to the exposures, the W buttons were exposed to either He, or D, plasma in PISCES-A for 2000 s at surface temperatures of 225–850 °C to create a variety of surfaces (surface blisters, subsurface nano-bubbles, fuzz). Erosion was spectroscopically measured from each DiMES sample, with the exception of the fuzzy W samples which showed almost undetectable WI emission. Post-exposure grazing incidence small angle x-ray scattering surface analysis showed the formation of 1.5 nm diameter He bubbles in themore » surface of W buttons after only a single DIII-D (3 s, ~150 ELMs) discharge, similar to the bubble layer resulting from the 2000 s. exposure in PISCES-A. No surface roughening, or damage, was detected on the samples after approximately 600 ELMs with energy density between 0.04–0.1 MJ m –2.« less