skip to main content
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information

This content will become publicly available on December 4, 2020

Title: Setting the H-mode pedestal structure: variations of particle source location using gas puff and pellet fueling

Abstract

Experiments in DIII-D reflect that a particle source location inside the top of the H-mode pedestal (pellets) maintains a higher pedestal pressure than an edge source (gas fueling) through a widening of the electron temperature pedestal with reduction of the temperature gradient. The result of these two fueling schemes on the H-mode pedestal structure was examined in DIII-D by comparing controlled pellet-fueled and gas-fueled discharges across a fueling scan up to 40 torr – L/s. High resolution electron profiles reveal that gas fueling lowers the pedestal pressure as the density profile shifts radially outwards and the separatrix density increases, while pellet fueling maintains a constant pedestal pressure. The neutral source locations from pellets and gas are determined with the PELLET and UEDGE codes, respectively, and quantify the particle source localization. Pellets offer significant ionization inside the pedestal top while gas puffing localizes ionization in the scrape-off-layer and pedestal foot, broadly consistent with the density profile structure influenced by the source. ELMs are observed to increase in frequency and reduce impurity content as fueling is increased. Stability analysis with ELITE shows that both conditions are near the type-I ELM corner of the peeling-ballooning stability diagram, which is altered significantly by themore » introduction of pellets. Since transport mechanisms are not observed to change substantially with particle source location, wider pedestals allow the pellet-fueled discharges to retain higher pedestal temperatures at similar pedestal densities. EPED1 is tested to capture the pedestal pressure, under-predicting the height with pellets and over-predicting the height with gas by ~ 15%. These results have vital implications for future reactors where pellet fueling will be the primary particle source due to an opaque scrape-off-layer by showing that the neutral source location plays a role in setting the structure of the H-mode pedestal.« less

Authors:
ORCiD logo [1];  [1];  [2]; ORCiD logo [1];  [3];  [2];  [4]; ORCiD logo [2];  [4];  [4];  [3]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Princeton Univ., NJ (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
General Atomics, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1577354
Grant/Contract Number:  
FC02-04ER54698; AC02-09CH11466; SC0015480; SC0015878; AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Name: Nuclear Fusion; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
plasma; tokamak; pellet; gas puff; pedestal

Citation Formats

Nelson, Andrew Oakleigh, Laggner, Florian M., Groebner, Richard J., Grierson, Brian A., Izacard, Olivier, Eldon, David, Shafer, Morgan, Leonard, Anthony W., Shiraki, Daisuke, Sontag, Aaron C., and Kolemen, Egemen. Setting the H-mode pedestal structure: variations of particle source location using gas puff and pellet fueling. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab5e65.
Nelson, Andrew Oakleigh, Laggner, Florian M., Groebner, Richard J., Grierson, Brian A., Izacard, Olivier, Eldon, David, Shafer, Morgan, Leonard, Anthony W., Shiraki, Daisuke, Sontag, Aaron C., & Kolemen, Egemen. Setting the H-mode pedestal structure: variations of particle source location using gas puff and pellet fueling. United States. doi:10.1088/1741-4326/ab5e65.
Nelson, Andrew Oakleigh, Laggner, Florian M., Groebner, Richard J., Grierson, Brian A., Izacard, Olivier, Eldon, David, Shafer, Morgan, Leonard, Anthony W., Shiraki, Daisuke, Sontag, Aaron C., and Kolemen, Egemen. Wed . "Setting the H-mode pedestal structure: variations of particle source location using gas puff and pellet fueling". United States. doi:10.1088/1741-4326/ab5e65.
@article{osti_1577354,
title = {Setting the H-mode pedestal structure: variations of particle source location using gas puff and pellet fueling},
author = {Nelson, Andrew Oakleigh and Laggner, Florian M. and Groebner, Richard J. and Grierson, Brian A. and Izacard, Olivier and Eldon, David and Shafer, Morgan and Leonard, Anthony W. and Shiraki, Daisuke and Sontag, Aaron C. and Kolemen, Egemen},
abstractNote = {Experiments in DIII-D reflect that a particle source location inside the top of the H-mode pedestal (pellets) maintains a higher pedestal pressure than an edge source (gas fueling) through a widening of the electron temperature pedestal with reduction of the temperature gradient. The result of these two fueling schemes on the H-mode pedestal structure was examined in DIII-D by comparing controlled pellet-fueled and gas-fueled discharges across a fueling scan up to 40 torr – L/s. High resolution electron profiles reveal that gas fueling lowers the pedestal pressure as the density profile shifts radially outwards and the separatrix density increases, while pellet fueling maintains a constant pedestal pressure. The neutral source locations from pellets and gas are determined with the PELLET and UEDGE codes, respectively, and quantify the particle source localization. Pellets offer significant ionization inside the pedestal top while gas puffing localizes ionization in the scrape-off-layer and pedestal foot, broadly consistent with the density profile structure influenced by the source. ELMs are observed to increase in frequency and reduce impurity content as fueling is increased. Stability analysis with ELITE shows that both conditions are near the type-I ELM corner of the peeling-ballooning stability diagram, which is altered significantly by the introduction of pellets. Since transport mechanisms are not observed to change substantially with particle source location, wider pedestals allow the pellet-fueled discharges to retain higher pedestal temperatures at similar pedestal densities. EPED1 is tested to capture the pedestal pressure, under-predicting the height with pellets and over-predicting the height with gas by ~ 15%. These results have vital implications for future reactors where pellet fueling will be the primary particle source due to an opaque scrape-off-layer by showing that the neutral source location plays a role in setting the structure of the H-mode pedestal.},
doi = {10.1088/1741-4326/ab5e65},
journal = {Nuclear Fusion},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {12}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on December 4, 2020
Publisher's Version of Record

Save / Share: