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

Wilcox, Robert S.; Baylor, Larry R.; Bortolon, Alessandro; Knolker, Matthias; Lasnier, C.J.; Shiraki, Daisuke; Bykov, Igor; Chrystal, Colin; Paz-Soldan, Carlos; Wingen, Andreas

doi:10.1088/1741-4326/ac3b8b

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

Journal Article · Wed Dec 22 00:00:00 EST 2021 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac3b8b· OSTI ID:1837404

^[1];

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

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

^[1]

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

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 from 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.

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

Grant/Contract Number:: AC05-00OR22725; AC02-09CH11466; FG02-07ER54917; AC52-07NA27344; FG02-16 04ER54761; FC02-04ER54698

OSTI ID:: 1837404

Alternate ID(s):: OSTI ID: 1843216; OSTI ID: 1860761

Report Number(s):: LLNL-JRNL-828736; TRN: US2300432

Journal Information:: Nuclear Fusion, Vol. 62, Issue 2; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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

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