Enhanced pedestal H-mode at low edge ion collisionality on NSTX
Abstract
The Enhanced Pedestal (EP) H-mode regime is an attractive wide-pedestal high-βp scenario for the National Spherical Torus Experiment Upgrade (NSTX-U) and next-step devices as it achieves enhanced energy confinement (H98y,2 > 1.5), large normalized pressure (βN > 5), and significant bootstrap fraction (fBS > 0.6) at Ip/BT = 2 MA/T. This regime is realized when the edge ion collisionality becomes sufficiently small that a positive feedback interaction occurs between a reduction in the ion neoclassical energy transport and an increase in the particle transport from pressure-driven edge instabilities. The EP H-mode was most often observed as a transition following a large edge-localized mode in conditions with low edge neutral recycling. It is hypothesized that the onset of pressure-driven instabilities prior to the full recovery of the neutral density leads to a temporary period with an elevated ion temperature gradient that triggers the transition to EP H-mode. Linear CGYRO and M3D-C1 calculations are compared to beam emission spectroscopy and magnetic spectroscopy in order to describe the evolution of the edge particle transport mechanisms during the ELM recovery and the saturated EP H-mode state. The observations are consistent with the hypothesis that the onset of pressure-driven edge instabilities, such as the kineticmore »
- Publication Date:
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 1643137
- Grant/Contract Number:
- AC02-09CH11466
- Resource Type:
- Publisher's Accepted Manuscript
- Journal Name:
- Physics of Plasmas
- Additional Journal Information:
- Journal Name: Physics of Plasmas Journal Volume: 27 Journal Issue: 7; Journal ID: ISSN 1070-664X
- Publisher:
- American Institute of Physics
- Country of Publication:
- United States
- Language:
- English
Citation Formats
Battaglia, D. J., Guttenfelder, W., Bell, R. E., Diallo, A., Ferraro, N., Fredrickson, E., Gerhardt, S. P., Kaye, S. M., Maingi, R., and Smith, D. R. Enhanced pedestal H-mode at low edge ion collisionality on NSTX. United States: N. p., 2020.
Web. doi:10.1063/5.0011614.
Battaglia, D. J., Guttenfelder, W., Bell, R. E., Diallo, A., Ferraro, N., Fredrickson, E., Gerhardt, S. P., Kaye, S. M., Maingi, R., & Smith, D. R. Enhanced pedestal H-mode at low edge ion collisionality on NSTX. United States. https://doi.org/10.1063/5.0011614
Battaglia, D. J., Guttenfelder, W., Bell, R. E., Diallo, A., Ferraro, N., Fredrickson, E., Gerhardt, S. P., Kaye, S. M., Maingi, R., and Smith, D. R. Fri .
"Enhanced pedestal H-mode at low edge ion collisionality on NSTX". United States. https://doi.org/10.1063/5.0011614.
@article{osti_1643137,
title = {Enhanced pedestal H-mode at low edge ion collisionality on NSTX},
author = {Battaglia, D. J. and Guttenfelder, W. and Bell, R. E. and Diallo, A. and Ferraro, N. and Fredrickson, E. and Gerhardt, S. P. and Kaye, S. M. and Maingi, R. and Smith, D. R.},
abstractNote = {The Enhanced Pedestal (EP) H-mode regime is an attractive wide-pedestal high-βp scenario for the National Spherical Torus Experiment Upgrade (NSTX-U) and next-step devices as it achieves enhanced energy confinement (H98y,2 > 1.5), large normalized pressure (βN > 5), and significant bootstrap fraction (fBS > 0.6) at Ip/BT = 2 MA/T. This regime is realized when the edge ion collisionality becomes sufficiently small that a positive feedback interaction occurs between a reduction in the ion neoclassical energy transport and an increase in the particle transport from pressure-driven edge instabilities. The EP H-mode was most often observed as a transition following a large edge-localized mode in conditions with low edge neutral recycling. It is hypothesized that the onset of pressure-driven instabilities prior to the full recovery of the neutral density leads to a temporary period with an elevated ion temperature gradient that triggers the transition to EP H-mode. Linear CGYRO and M3D-C1 calculations are compared to beam emission spectroscopy and magnetic spectroscopy in order to describe the evolution of the edge particle transport mechanisms during the ELM recovery and the saturated EP H-mode state. The observations are consistent with the hypothesis that the onset of pressure-driven edge instabilities, such as the kinetic ballooning mode and kink-peeling mode, can be responsible for the increased particle transport in EP H-mode.},
doi = {10.1063/5.0011614},
journal = {Physics of Plasmas},
number = 7,
volume = 27,
place = {United States},
year = {Fri Jul 24 00:00:00 EDT 2020},
month = {Fri Jul 24 00:00:00 EDT 2020}
}
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https://doi.org/10.1063/5.0011614
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