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Title: H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX

Abstract

High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a {approx}100 {micro}sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges.more » Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value.« less

Authors:
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Publication Date:
Research Org.:
Princeton Plasma Physics Lab., Princeton, NJ (US)
Sponsoring Org.:
USDOE Office of Science (SC) (US)
OSTI Identifier:
836092
Report Number(s):
PPPL-4016
TRN: US0500492
DOE Contract Number:  
AC02-76CH03073
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 28 Oct 2004
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ASPECT RATIO; BOOTSTRAP CURRENT; EDGE LOCALIZED MODES; HEATING; PHYSICS; PLASMA; PLASMA PRESSURE; STORED ENERGY; TURBULENCE; DIVERTORS; EDGE PLASMA; TOKAMAKS, NSTX

Citation Formats

R. Maingi, C.E. Bush, E.D. Fredrickson, D.A. Gates, S.M. Kaye, B.P. LeBlanc, J.E. Menard, H. Meyer, D. Mueller, N. Nishino, A.L. Roquemore, S.A. Sabbagh, K. Tritz, S.J. Zweben, M.G. Bell, R.E. Bell, T. Biewer, J.A. Boedo, D.W. Johnson, R. Kaita, H.W. Kugel, R.J. Maqueda, T. Munsat, R. Raman, V.A. Soukhanovskii, T. Stevenson, and D. Stutman. H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX. United States: N. p., 2004. Web. doi:10.2172/836092.
R. Maingi, C.E. Bush, E.D. Fredrickson, D.A. Gates, S.M. Kaye, B.P. LeBlanc, J.E. Menard, H. Meyer, D. Mueller, N. Nishino, A.L. Roquemore, S.A. Sabbagh, K. Tritz, S.J. Zweben, M.G. Bell, R.E. Bell, T. Biewer, J.A. Boedo, D.W. Johnson, R. Kaita, H.W. Kugel, R.J. Maqueda, T. Munsat, R. Raman, V.A. Soukhanovskii, T. Stevenson, & D. Stutman. H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX. United States. doi:10.2172/836092.
R. Maingi, C.E. Bush, E.D. Fredrickson, D.A. Gates, S.M. Kaye, B.P. LeBlanc, J.E. Menard, H. Meyer, D. Mueller, N. Nishino, A.L. Roquemore, S.A. Sabbagh, K. Tritz, S.J. Zweben, M.G. Bell, R.E. Bell, T. Biewer, J.A. Boedo, D.W. Johnson, R. Kaita, H.W. Kugel, R.J. Maqueda, T. Munsat, R. Raman, V.A. Soukhanovskii, T. Stevenson, and D. Stutman. Thu . "H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX". United States. doi:10.2172/836092. https://www.osti.gov/servlets/purl/836092.
@article{osti_836092,
title = {H-Mode Turbulence, Power Threshold, ELM, and Pedestal Studies in NSTX},
author = {R. Maingi and C.E. Bush and E.D. Fredrickson and D.A. Gates and S.M. Kaye and B.P. LeBlanc and J.E. Menard and H. Meyer and D. Mueller and N. Nishino and A.L. Roquemore and S.A. Sabbagh and K. Tritz and S.J. Zweben and M.G. Bell and R.E. Bell and T. Biewer and J.A. Boedo and D.W. Johnson and R. Kaita and H.W. Kugel and R.J. Maqueda and T. Munsat and R. Raman and V.A. Soukhanovskii and T. Stevenson and D. Stutman},
abstractNote = {High-confinement mode (H-mode) operation plays a crucial role in NSTX [National Spherical Torus Experiment] research, allowing higher beta limits due to reduced plasma pressure peaking, and long-pulse operation due to high bootstrap current fraction. Here, new results are presented in the areas of edge localized modes (ELMs), H-mode pedestal physics, L-H turbulence, and power threshold studies. ELMs of several other types (as observed in conventional aspect ratio tokamaks) are often observed: (1) large, Type I ELMs, (2) ''medium'' Type II/III ELMs, and (3) giant ELMs which can reduce stored energy by up to 30% in certain conditions. In addition, many high-performance discharges in NSTX have tiny ELMs (newly termed Type V), which have some differences as compared with ELM types in the published literature. The H-mode pedestal typically contains between 25-33% of the total stored energy, and the NSTX pedestal energy agrees reasonably well with a recent international multi-machine scaling. We find that the L-H transition occurs on a {approx}100 {micro}sec timescale as viewed by a gas puff imaging diagnostic, and that intermittent quiescent periods precede the final transition. A power threshold identity experiment between NSTX and MAST shows comparable loss power at the L-H transition in balanced double-null discharges. Both machines require more power for the L-H transition as the balance is shifted toward lower single null. High field side gas fueling enables more reliable H-mode access, but does not always lead to a lower power threshold e.g., with a reduction of the duration of early heating. Finally the edge plasma parameters just before the L-H transition were compared with theories of the transition. It was found that while some theories can separate well-developed L- and H-mode data, they have little predictive value.},
doi = {10.2172/836092},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Oct 28 00:00:00 EDT 2004},
month = {Thu Oct 28 00:00:00 EDT 2004}
}

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