Title: Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

Abstract

Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25%–50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting frommore » ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.« less

Authors:

Wilcox, Robert S.  ^[1];

• Search DOE PAGES for author "Wilcox, Robert S."
• Search DOE PAGES for ORCID "0000-0003-1369-1739"

Baylor, Larry R.  ^[1];

• Search DOE PAGES for author "Baylor, Larry R."
• Search DOE PAGES for ORCID "0000-0002-0325-7771"

Bortolon, Alessandro ^[2]; Knolker, Matthias ^[3]; Lasnier, C.J. ^[4]; Shiraki, Daisuke  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-1452-6949"

Bykov, Igor ^[5]; Chrystal, Colin ^[3]; Paz-Soldan, Carlos ^[6]; Wingen, Andreas  ^[1]

• Search DOE PAGES for author "Wingen, Andreas"
• Search DOE PAGES for ORCID "0000-0001-8855-1349"

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
3. General Atomics, San Diego, CA (United States)
4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
5. Univ. of California, San Diego, CA (United States)
6. Columbia Univ., New York, NY (United States)

Publication Date:

Wed Dec 22 00:00:00 EST 2021

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); General Atomics, San Diego, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1837404

Alternate Identifier(s):

OSTI ID: 1843216; OSTI ID: 1860761

Report Number(s):

LLNL-JRNL-828736
Journal ID: ISSN 0029-5515; TRN: US2300432

Grant/Contract Number:  

AC05-00OR22725; AC02-09CH11466; FG02-07ER54917; AC52-07NA27344; FG02-16 04ER54761; FC02-04ER54698

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 62; Journal Issue: 2; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELMs, pellets, tokamak