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Title: Advances in understanding of high- Z material erosion and re-deposition in low- Z wall environment in DIII-D

Abstract

Dedicated DIII-D experiments coupled with modeling reveal that the net erosion rate of high-Z materials, i.e. Mo and W, is strongly affected by carbon concentration in the plasma and the magnetic pre-sheath properties. We have investigated different methods such as electrical biasing and local gas injection to control high-Z material erosion. The net erosion rate of high-Z materials is significantly reduced due to the high local re-deposition ratio. The ERO modeling shows that the local re-deposition ratio is mainly controlled by the electric field and plasma density within the magnetic pre-sheath. The net erosion can be significantly suppressed by reducing the sheath potential drop. A high carbon impurity concentration in the background plasma is also found to reduce the net erosion rate of high-Z materials. Both DIII-D experiments and modeling show that local 13CH 4 injection can create a carbon coating on the metal surface. The profile of 13C deposition provides quantitative information on radial transport due to E × B drift and the cross-field diffusion. The deuterium gas injection upstream of the W sample can reduce W net erosion rate by plasma perturbation. The inter-ELM W erosion we measured in H-mode plasmas, rates at different radial locations are wellmore » reproduced by ERO modeling taking into account charge-state-resolved carbon ion flux in the background plasma calculated using the OEDGE code.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [7];  [2];  [5];  [5];  [3];  [5];  [8];  [6];  [9];  [5];  [9];  [9];  [5];  [5] more »;  [10];  [7];  [8];  [4] « less
  1. Oak Ridge Associated Univ., Oak Ridge, TN (United States); Chinese Academy of Sciences (CAS), Beijing (China). Inst. of Plasma Physics; General Atomics, San Diego, CA (United States)
  2. Univ. of California, San Diego, CA (United States)
  3. Univ. of Toronto, ON (Canada). Inst. for Aerospace Studies
  4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  5. General Atomics, San Diego, CA (United States)
  6. Julich Research Centre (Germany). Inst. of Energy and Climate Research- Plasma Physics
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  8. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
  9. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  10. Univ. of Vienna (Austria). Fusion @OAW. Inst. of Applied Physics
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1357016
Alternate Identifier(s):
OSTI ID: 1374606; OSTI ID: 1374610
Report Number(s):
SAND-2017-0016J
Journal ID: ISSN 0029-5515; 650168
Grant/Contract Number:
AC04-94AL85000; GA-DE-SC0008698; AC05-06OR23100; FG02-07ER54917; AC05-00OR22725; FC02-04ER54698; AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 5; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; erosion; deposition; high-Z materials; impurity

Citation Formats

Ding, R., Rudakov, D. L., Stangeby, P. C., Wampler, W. R., Abrams, T., Brezinsek, S., Briesemeister, A., Bykov, I., Chan, V. S., Chrobak, C. P., Elder, J. D., Guo, H. Y., Guterl, J., Kirschner, A., Lasnier, C. J., Leonard, A. W., Makowski, M. A., McLean, A. G., Snyder, P. B., Thomas, D. M., Tskhakaya, D., Unterberg, E. A., Wang, H. Q., and Watkins, J. G. Advances in understanding of high- Z material erosion and re-deposition in low- Z wall environment in DIII-D. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa6451.
Ding, R., Rudakov, D. L., Stangeby, P. C., Wampler, W. R., Abrams, T., Brezinsek, S., Briesemeister, A., Bykov, I., Chan, V. S., Chrobak, C. P., Elder, J. D., Guo, H. Y., Guterl, J., Kirschner, A., Lasnier, C. J., Leonard, A. W., Makowski, M. A., McLean, A. G., Snyder, P. B., Thomas, D. M., Tskhakaya, D., Unterberg, E. A., Wang, H. Q., & Watkins, J. G. Advances in understanding of high- Z material erosion and re-deposition in low- Z wall environment in DIII-D. United States. doi:10.1088/1741-4326/aa6451.
Ding, R., Rudakov, D. L., Stangeby, P. C., Wampler, W. R., Abrams, T., Brezinsek, S., Briesemeister, A., Bykov, I., Chan, V. S., Chrobak, C. P., Elder, J. D., Guo, H. Y., Guterl, J., Kirschner, A., Lasnier, C. J., Leonard, A. W., Makowski, M. A., McLean, A. G., Snyder, P. B., Thomas, D. M., Tskhakaya, D., Unterberg, E. A., Wang, H. Q., and Watkins, J. G. Fri . "Advances in understanding of high- Z material erosion and re-deposition in low- Z wall environment in DIII-D". United States. doi:10.1088/1741-4326/aa6451. https://www.osti.gov/servlets/purl/1357016.
@article{osti_1357016,
title = {Advances in understanding of high- Z material erosion and re-deposition in low- Z wall environment in DIII-D},
author = {Ding, R. and Rudakov, D. L. and Stangeby, P. C. and Wampler, W. R. and Abrams, T. and Brezinsek, S. and Briesemeister, A. and Bykov, I. and Chan, V. S. and Chrobak, C. P. and Elder, J. D. and Guo, H. Y. and Guterl, J. and Kirschner, A. and Lasnier, C. J. and Leonard, A. W. and Makowski, M. A. and McLean, A. G. and Snyder, P. B. and Thomas, D. M. and Tskhakaya, D. and Unterberg, E. A. and Wang, H. Q. and Watkins, J. G.},
abstractNote = {Dedicated DIII-D experiments coupled with modeling reveal that the net erosion rate of high-Z materials, i.e. Mo and W, is strongly affected by carbon concentration in the plasma and the magnetic pre-sheath properties. We have investigated different methods such as electrical biasing and local gas injection to control high-Z material erosion. The net erosion rate of high-Z materials is significantly reduced due to the high local re-deposition ratio. The ERO modeling shows that the local re-deposition ratio is mainly controlled by the electric field and plasma density within the magnetic pre-sheath. The net erosion can be significantly suppressed by reducing the sheath potential drop. A high carbon impurity concentration in the background plasma is also found to reduce the net erosion rate of high-Z materials. Both DIII-D experiments and modeling show that local 13CH4 injection can create a carbon coating on the metal surface. The profile of 13C deposition provides quantitative information on radial transport due to E × B drift and the cross-field diffusion. The deuterium gas injection upstream of the W sample can reduce W net erosion rate by plasma perturbation. The inter-ELM W erosion we measured in H-mode plasmas, rates at different radial locations are well reproduced by ERO modeling taking into account charge-state-resolved carbon ion flux in the background plasma calculated using the OEDGE code.},
doi = {10.1088/1741-4326/aa6451},
journal = {Nuclear Fusion},
number = 5,
volume = 57,
place = {United States},
year = {Fri Mar 24 00:00:00 EDT 2017},
month = {Fri Mar 24 00:00:00 EDT 2017}
}

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  • Dedicated DIII-D experiments coupled with modeling reveal that the net erosion rate of high- Z materials, i.e., Mo and W, is strongly affected by carbon concentration in the plasma and the magnetic pre-sheath properties. Different methods such as electrical biasing and local gas injection have been investigated to control high-Z material erosion. The net erosion rate of high-Z materials is significantly reduced due to the high local re-deposition ratio. The ERO modeling shows that the local re-deposition ratio is mainly controlled by the electric field and plasma density within the magnetic pre-sheath. The net erosion can be significantly suppressed bymore » reducing the sheath potential drop. A high carbon impurity concentration in the background plasma is also found to reduce the net erosion rate of high-Z materials. Both DIIID experiments and modeling show that local 13CH 4 injection can create a carbon coating on the metal surface. The profile of 13C deposition provides quantitative information on radial transport due to E×B drift and the cross-field diffusion. The deuterium gas injection upstream of the W sample can reduce W net erosion rate by plasma perturbation. In H-mode plasmas, the measured inter-ELM W erosion rates at different radial locations are well reproduced by ERO modeling taking into account charge-state-resolved carbon ion flux in the background plasma calculated using the OEDGE code.« less
  • Dedicated DIII-D experiments coupled with modeling reveal that the net erosion rate of high- Z materials, i.e., Mo and W, is strongly affected by carbon concentration in the plasma and the magnetic pre-sheath properties. Different methods such as electrical biasing and local gas injection have been investigated to control high-Z material erosion. The net erosion rate of high-Z materials is significantly reduced due to the high local re-deposition ratio. The ERO modeling shows that the local re-deposition ratio is mainly controlled by the electric field and plasma density within the magnetic pre-sheath. The net erosion can be significantly suppressed bymore » reducing the sheath potential drop. A high carbon impurity concentration in the background plasma is also found to reduce the net erosion rate of high-Z materials. Both DIIID experiments and modeling show that local 13CH 4 injection can create a carbon coating on the metal surface. The profile of 13C deposition provides quantitative information on radial transport due to E×B drift and the cross-field diffusion. The deuterium gas injection upstream of the W sample can reduce W net erosion rate by plasma perturbation. In H-mode plasmas, the measured inter-ELM W erosion rates at different radial locations are well reproduced by ERO modeling taking into account charge-state-resolved carbon ion flux in the background plasma calculated using the OEDGE code.« less
  • Here, we present measurements and modeling of aluminum erosion and redeposition experiments in separate helium and deuterium low power, low density L-mode plasmas at the outer divertor strike point of DIII-D to provide a low-Z material benchmark dataset for tokamak erosion-deposition modeling codes. Coatings of Al ~100nm thick were applied to ideal (smooth) and realistic (rough) surfaces and exposed to repeat plasma discharges using the DiMES probe. Redeposition and re-erosion in all cases was primarily in the downstream toroidal field direction, evident from both in-situ spectroscopic and post-mortem non spectroscopic measurements. The gross Al erosion yield estimated from both Hemore » and D plasma exposures was ~40-70% of the expected erosion yield based on theoretical physical sputtering yields. However, the multi-step redeposition and re-erosion process, and hence the measured net erosion yield and material migration, was found to be influenced by the surface roughness and/or porosity. On rough surfaces, the fraction of the eroded Al coating found redeposited outside the original coating area was 25x higher than on smooth surfaces. The amount of Al found redeposited on the rough substrate was in fact proportional to the net eroded Al, suggesting an accumulation of deposited Al in surface pores and other areas shadowed from re-erosion. In order to determine the fraction and distribution of eroded Al returning to the surface, a simple model for erosion and redeposition was developed and fitted to the measurements. The model presented here reproduces many of the observed results in these experiments by using theoretically calculated sputtering yields, calculating surface composition changes and erosion rates in time, assuming a spatial distribution function for redepositing atoms, and accounting for deposit trapping in pores. The results of the model fits reveal that total redeposition fraction increases with higher plasma temperature (~30% for 15-18eV plasmas, and ~45% for 25-30eV plasmas), and that 50% of the atoms redepositing on rough surfaces accumulated in shadowed areas.« less
  • Here, we present measurements and modeling of aluminum erosion and redeposition experiments in separate helium and deuterium low power, low density L-mode plasmas at the outer divertor strike point of DIII-D to provide a low-Z material benchmark dataset for tokamak erosion-deposition modeling codes. Coatings of Al ~100nm thick were applied to ideal (smooth) and realistic (rough) surfaces and exposed to repeat plasma discharges using the DiMES probe. Redeposition and re-erosion in all cases was primarily in the downstream toroidal field direction, evident from both in-situ spectroscopic and post-mortem non spectroscopic measurements. The gross Al erosion yield estimated from both Hemore » and D plasma exposures was ~40-70% of the expected erosion yield based on theoretical physical sputtering yields. However, the multi-step redeposition and re-erosion process, and hence the measured net erosion yield and material migration, was found to be influenced by the surface roughness and/or porosity. On rough surfaces, the fraction of the eroded Al coating found redeposited outside the original coating area was 25x higher than on smooth surfaces. The amount of Al found redeposited on the rough substrate was in fact proportional to the net eroded Al, suggesting an accumulation of deposited Al in surface pores and other areas shadowed from re-erosion. In order to determine the fraction and distribution of eroded Al returning to the surface, a simple model for erosion and redeposition was developed and fitted to the measurements. The model presented here reproduces many of the observed results in these experiments by using theoretically calculated sputtering yields, calculating surface composition changes and erosion rates in time, assuming a spatial distribution function for redepositing atoms, and accounting for deposit trapping in pores. The results of the model fits reveal that total redeposition fraction increases with higher plasma temperature (~30% for 15-18eV plasmas, and ~45% for 25-30eV plasmas), and that 50% of the atoms redepositing on rough surfaces accumulated in shadowed areas.« less