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Title: H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment

Abstract

H-mode is obtained at $$A\sim 1.2$$ in the Pegasus Toroidal Experiment via Ohmic heating, high-field-side fueling, and low edge recycling in both limited and diverted magnetic topologies. These H-mode plasmas show the formation of edge current and pressure pedestals and a doubling of the energy confinement time to $${{H}_{98y,2}}\sim 1$$ . The L–H power threshold $${{P}_{\text{LH}}}$$ increases with density, and there is no $${{P}_{\text{LH}}}$$ minimum observed in the attainable density space. The power threshold is equivalent in limited and diverted plasmas, consistent with the FM3 model. However, the measured $${{P}_{\text{LH}}}$$ is $$\sim 15\,\,\times $$ higher than that predicted by conventional International Tokamak Physics Activity (ITPA) scalings, and $${{P}_{\text{LH}}}/{{P}_{\text{ITPA}08}}$$ increases as $$A\to 1$$ . Small ELMs are present at low input power $${{P}_{\text{IN}}}\sim {{P}_{\text{LH}}}$$ , with toroidal mode number $$n\leqslant 4$$ . At $${{P}_{\text{IN}}}\gg {{P}_{\text{LH}}}$$ , they transition to large ELMs with intermediate 5 < n < 15. The dominant-n component of a large ELM grows exponentially, while other components evolve nonlinearly and can damp prior to the crash. Direct measurements of the current profile in the pedestal region show that both ELM types exhibit a generation of a current-hole, followed by a pedestal recovery. Large ELMs are shown to further expel a current-carrying filament. Small ELM suppression via injection of low levels of helical current into the edge plasma region is also indicated.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Univ. of Wisconsin-Madison, Madison, WI (United States)
Publication Date:
Research Org.:
Univ. of Wisconsin-Madison, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1333880
Alternate Identifier(s):
OSTI ID: 1327562
Grant/Contract Number:  
FG02-96ER54375
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 2; Related Information: K.E. Thome, M.W. Bongard, J.L. Barr, G.M. Bodner, M.G. Burke, R.J. Fonck, D.M. Kriete, J.M. Perry, J.A. Reusch, and D.J. Schlossberg, "Public Data Set: H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment," DOI: 10.18138/1236495; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; H-mode; spherical tokamaks; equilibrium reconstructions; energy confinement; ELM; ELM dynamics

Citation Formats

Thome, Kathleen E., Bongard, Michael W., Barr, Jayson L., Bodner, Grant M., Burke, Marcus G., Fonck, Raymonf J., Kriete, David M., Perry, Justin M., Reusch, Joshua A., and Schlossberg, David J. H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment. United States: N. p., 2016. Web. doi:10.1088/0029-5515/57/2/022018.
Thome, Kathleen E., Bongard, Michael W., Barr, Jayson L., Bodner, Grant M., Burke, Marcus G., Fonck, Raymonf J., Kriete, David M., Perry, Justin M., Reusch, Joshua A., & Schlossberg, David J. H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment. United States. doi:10.1088/0029-5515/57/2/022018.
Thome, Kathleen E., Bongard, Michael W., Barr, Jayson L., Bodner, Grant M., Burke, Marcus G., Fonck, Raymonf J., Kriete, David M., Perry, Justin M., Reusch, Joshua A., and Schlossberg, David J. Fri . "H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment". United States. doi:10.1088/0029-5515/57/2/022018. https://www.osti.gov/servlets/purl/1333880.
@article{osti_1333880,
title = {H-mode plasmas at very low aspect ratio on the Pegasus Toroidal Experiment},
author = {Thome, Kathleen E. and Bongard, Michael W. and Barr, Jayson L. and Bodner, Grant M. and Burke, Marcus G. and Fonck, Raymonf J. and Kriete, David M. and Perry, Justin M. and Reusch, Joshua A. and Schlossberg, David J.},
abstractNote = {H-mode is obtained at $A\sim 1.2$ in the Pegasus Toroidal Experiment via Ohmic heating, high-field-side fueling, and low edge recycling in both limited and diverted magnetic topologies. These H-mode plasmas show the formation of edge current and pressure pedestals and a doubling of the energy confinement time to ${{H}_{98y,2}}\sim 1$ . The L–H power threshold ${{P}_{\text{LH}}}$ increases with density, and there is no ${{P}_{\text{LH}}}$ minimum observed in the attainable density space. The power threshold is equivalent in limited and diverted plasmas, consistent with the FM3 model. However, the measured ${{P}_{\text{LH}}}$ is $\sim 15\,\,\times $ higher than that predicted by conventional International Tokamak Physics Activity (ITPA) scalings, and ${{P}_{\text{LH}}}/{{P}_{\text{ITPA}08}}$ increases as $A\to 1$ . Small ELMs are present at low input power ${{P}_{\text{IN}}}\sim {{P}_{\text{LH}}}$ , with toroidal mode number $n\leqslant 4$ . At ${{P}_{\text{IN}}}\gg {{P}_{\text{LH}}}$ , they transition to large ELMs with intermediate 5 < n < 15. The dominant-n component of a large ELM grows exponentially, while other components evolve nonlinearly and can damp prior to the crash. Direct measurements of the current profile in the pedestal region show that both ELM types exhibit a generation of a current-hole, followed by a pedestal recovery. Large ELMs are shown to further expel a current-carrying filament. Small ELM suppression via injection of low levels of helical current into the edge plasma region is also indicated.},
doi = {10.1088/0029-5515/57/2/022018},
journal = {Nuclear Fusion},
number = 2,
volume = 57,
place = {United States},
year = {Fri Sep 30 00:00:00 EDT 2016},
month = {Fri Sep 30 00:00:00 EDT 2016}
}

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