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Title: Enhanced Pedestal H-mode at low edge ion collisionality on NSTX

Abstract

The Enhanced Pedestal (EP) H-mode regime is an attractive wide-pedestal ELM-free high-betap scenario for NSTX-U and next-step devices as it achieves enhanced energy confinement (H98y,2 > 1.5), large normalized pressure (betaN > 5) and significant bootstrap fraction (f_BS > 0.6) at I_p/B_T = 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. EP H-mode was most often observed as a transition following a large ELM 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 elevated ion temperature gradient that triggers the transition to EP H-mode. Linear CGYRO and M3D-C1 calculations are compared to beam emission spectroscopy (BES) 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 KBM and kink-peeling, can be responsible for themore » increased particle transport in EP H-mode.« less

Authors:
; ; ; ; ; ; ; ;
Publication Date:
DOE Contract Number:  
AC02-09CH11466
Product Type:
Dataset
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
Keywords:
spherical tokamaks; magnetic plasma confinement; turbulence and transport; edge and boundary physics; NSTX; H-mode
OSTI Identifier:
1661168
DOI:
https://doi.org/10.11578/1661168

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:10.11578/1661168.
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. doi:https://doi.org/10.11578/1661168
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. 2020. "Enhanced Pedestal H-mode at low edge ion collisionality on NSTX". United States. doi:https://doi.org/10.11578/1661168. https://www.osti.gov/servlets/purl/1661168. Pub date:Wed Jul 08 00:00:00 EDT 2020
@article{osti_1661168,
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 ELM-free high-betap scenario for NSTX-U and next-step devices as it achieves enhanced energy confinement (H98y,2 > 1.5), large normalized pressure (betaN > 5) and significant bootstrap fraction (f_BS > 0.6) at I_p/B_T = 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. EP H-mode was most often observed as a transition following a large ELM 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 elevated ion temperature gradient that triggers the transition to EP H-mode. Linear CGYRO and M3D-C1 calculations are compared to beam emission spectroscopy (BES) 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 KBM and kink-peeling, can be responsible for the increased particle transport in EP H-mode.},
doi = {10.11578/1661168},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2020},
month = {7}
}