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

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.

doi:10.1088/0029-5515/57/2/022018

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

Journal Article · Fri Sep 30 00:00:00 EDT 2016 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/57/2/022018· OSTI ID:1333880

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Univ. of Wisconsin-Madison, Madison, WI (United States); University of Wisconsin-Madison
Univ. of Wisconsin-Madison, Madison, WI (United States)

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.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of Wisconsin-Madison, Madison, WI (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)

Grant/Contract Number:: FG02-96ER54375

OSTI ID:: 1333880

Alternate ID(s):: OSTI ID: 1327562
OSTI ID: 22925603

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 2 Vol. 57; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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Public Data Set: H-mode Plasmas at Very Low Aspect Ratio on the Pegasus Toroidal Experiment Thome, Kathreen; Bongard, Michael; Barr, Jayson https://doi.org/10.18138/1236495	dataset	January 2016
Public Data Set: Continuous, Edge Localized Ion Heating During Non-Solenoidal Plasma Startup and Sustainment in a Low Aspect Ratio Tokamak Burke, Marcus; Barr, Jayson; Bongard, Michael https://doi.org/10.18138/1336395	dataset	January 2017
Public Data Set: A Power-Balance Model for Local Helicity Injection Startup in a Spherical Tokamak Barr, J. L.; Bongard, M. W.; Burke, M. G. Pegasus Public Data Sets https://doi.org/10.18138/1345037	dataset	May 2018
Public Data Set: Non-inductively Driven Tokamak Plasmas at Near-Unity βt in the Pegasus Toroidal Experiment Reusch, Joshua; Bodner, Grant; Bongard, Michael Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5017966, 1 file (5.1 MB) https://doi.org/10.18138/1410490	dataset	March 2018
Public Data Set: Initiation and Sustainment of Tokamak Plasmas with Local Helicity Injection as the Majority Current Drive Perry, Justin; Bodner, Grant; Bongard, Michael Pegasus-Supplementary information for journal article at DOI: https://doi.org/10.1088/1741-4326/aac72e, 1 file (17.1 MB) https://doi.org/10.18138/1419641	dataset	July 2018
Public Data Set: Radially Scanning Magnetic Probes to Study Local Helicity Injection Dynamics Richner, Nathan; Bongard, Michael; Fonck, Raymond Pegasus-Supplementary information for journal article at DOI: 10.1063/1.5036527, 1 file (9.4 MB) https://doi.org/10.18138/1432455	dataset	July 2018
Public Data Set: Spatial Heterodyne Spectroscopy for High Speed Measurements of Stark Split Neutral Beam Emission in a High Temperature Plasma Burke, Marcus; Fonck, Raymond; McKee, George University of Wisconsin-Madison https://doi.org/10.18138/1435641	dataset	January 2018
Public Data Set: Advancing Local Helicity Injection for Non-Solenoidal Tokamak Startup Bongard, Michael; Bodner, Grant; Burke, Marcus University of Wisconsin-Madison https://doi.org/10.18138/1489772	dataset	January 2019
Non-inductively driven tokamak plasmas at near-unity βt in the P egasus toroidal experiment Reusch, J. A.; Bodner, G. M.; Bongard, M. W. Physics of Plasmas, Vol. 25, Issue 5 https://doi.org/10.1063/1.5017966	journal	May 2018
Radially scanning magnetic probes to study local helicity injection dynamics Richner, N. J.; Bongard, M. W.; Fonck, R. J. Review of Scientific Instruments, Vol. 89, Issue 10, Article No. 10J103 https://doi.org/10.1063/1.5036527	journal	October 2018
Long-lived coupled peeling ballooning modes preceding ELMs on JET Perez von Thun, C.; Frassinetti, L.; Horvath, L. Nuclear Fusion, Vol. 59, Issue 5 https://doi.org/10.1088/1741-4326/ab0031	journal	March 2019
Formation of the non-axisymmetric helical current driven by a biased electrode in the scrape-off layer on J-TEXT Wang, Nengchao; Song, Zebao; Liang, Y. Nuclear Fusion, Vol. 59, Issue 9 https://doi.org/10.1088/1741-4326/ab2d03	journal	August 2019
Noninductively Driven Tokamak Plasmas at Near-Unity Toroidal Beta Schlossberg, D. J.; Bodner, G. M.; Bongard, M. W. Physical Review Letters, Vol. 119, Issue 3, Article No. 035001 https://doi.org/10.1103/physrevlett.119.035001	journal	July 2017

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