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Title: Multi-species impurity granule injection and mass deposition projections in NSTX-U discharges

Abstract

Here, by employing a neutral gas shielding (NGS) model to characterize impurity granule injection, the ablation rates for three different species of granule: lithium, boron, and carbon, are determined. Utilizing the duration of ablation events recorded on experiments performed at DIII-D to calibrate the NGS model, we quantify the ablation rate with respect to the plasma density profile. The species-specific granule shielding constant is then used to model granule ablation within NSTX-U discharges. Simulations of 300, 500 and 700 micron diameter granules injected at 50 m s –1 are presented for NSTX-U L-mode type plasmas, as well as H-mode discharges with low natural ELM frequency. Additionally, ablation calculations of 500 micron granules of each species are presented at velocities ranging from 50–150 m s –1. In H-mode discharges these simulations show that the majority of the injected granule is ablated within or just past the edge steep gradient region. At this radial position, the perturbation to the background plasma generated by the ablating granule can lead to conditions advantageous for the rapid triggering of ELM crashes.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1362046
Grant/Contract Number:
AC02-09CH11466
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 7; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; granule injection; ELM pacing; neutral gas shielding

Citation Formats

Lunsford, R., Bortolon, A., Roquemore, A. L., Mansfield, D. K., Jaworski, M. A., Kaita, R., Maingi, R., and Nagy, A. Multi-species impurity granule injection and mass deposition projections in NSTX-U discharges. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa6cd3.
Lunsford, R., Bortolon, A., Roquemore, A. L., Mansfield, D. K., Jaworski, M. A., Kaita, R., Maingi, R., & Nagy, A. Multi-species impurity granule injection and mass deposition projections in NSTX-U discharges. United States. doi:10.1088/1741-4326/aa6cd3.
Lunsford, R., Bortolon, A., Roquemore, A. L., Mansfield, D. K., Jaworski, M. A., Kaita, R., Maingi, R., and Nagy, A. Tue . "Multi-species impurity granule injection and mass deposition projections in NSTX-U discharges". United States. doi:10.1088/1741-4326/aa6cd3. https://www.osti.gov/servlets/purl/1362046.
@article{osti_1362046,
title = {Multi-species impurity granule injection and mass deposition projections in NSTX-U discharges},
author = {Lunsford, R. and Bortolon, A. and Roquemore, A. L. and Mansfield, D. K. and Jaworski, M. A. and Kaita, R. and Maingi, R. and Nagy, A.},
abstractNote = {Here, by employing a neutral gas shielding (NGS) model to characterize impurity granule injection, the ablation rates for three different species of granule: lithium, boron, and carbon, are determined. Utilizing the duration of ablation events recorded on experiments performed at DIII-D to calibrate the NGS model, we quantify the ablation rate with respect to the plasma density profile. The species-specific granule shielding constant is then used to model granule ablation within NSTX-U discharges. Simulations of 300, 500 and 700 micron diameter granules injected at 50 m s–1 are presented for NSTX-U L-mode type plasmas, as well as H-mode discharges with low natural ELM frequency. Additionally, ablation calculations of 500 micron granules of each species are presented at velocities ranging from 50–150 m s–1. In H-mode discharges these simulations show that the majority of the injected granule is ablated within or just past the edge steep gradient region. At this radial position, the perturbation to the background plasma generated by the ablating granule can lead to conditions advantageous for the rapid triggering of ELM crashes.},
doi = {10.1088/1741-4326/aa6cd3},
journal = {Nuclear Fusion},
number = 7,
volume = 57,
place = {United States},
year = {Tue May 16 00:00:00 EDT 2017},
month = {Tue May 16 00:00:00 EDT 2017}
}

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  • In this paper, we present simulations of pedestal control by lithium granule injection (LGI) in NSTX. A model for small granule ablation has been implemented in the M3D-C1 code (Jardin et al 2012 Comput. Sci. Discovery 5 014002), allowing the simulation of realistic lithium granule injections. 2D and 3D simulations of Li injections in NSTX H-mode plasmas are performed and the effect of granule size, injection angle and velocity on the pedestal gradient increase is studied. The amplitude of the local pressure perturbation caused by the granules is found to be highly dependent on the solid granule size. Adjusting themore » granule injection velocity allows one to inject more particles at the pedestal top. 3D simulations show the destabilization of high order MHD modes whose amplitude is directly linked to the localized pressure perturbation, which is found to depend on the toroidal localization of the granule density source.« less
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