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Title: Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U

Abstract

Recently published scenarios for fully non-inductive startup and operation on the National SphericalTorus eXperiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) show ElectronCyclotron Resonance Heating (ECRH) as an important component in preparing a target plasma forefficient High Harmonic Fast Wave and Neutral Beam heating. The modeling of the propagation andabsorption of EC waves in the evolving plasma is required to define the most effective window ofoperation, and to optimize the launcher geometry for maximal heating and current drive during thiswindow. Here, we extend a previous optimization of O1-mode ECRH on NSTX-U to account for thefull time-dependent performance of the ECRH using simulations performed with TRANSP. We findthat the evolution of the density profile has a prominent role in the optimization by defining the timewindow of operation, which in certain cases may be a more important metric to compare launcherperformance than the average power absorption. This feature cannot be captured by analysis on staticprofiles, and should be accounted for when optimizing ECRH on any device that operates near thecutoff density. Additionally, the utility of the electron Bernstein wave (EBW) in driving current andgenerating closed flux surfaces in the early startup phase has been demonstrated on a number ofdevices.more » Using standalone GENRAY simulations, we find that efficient EBW current drive ispossible on NSTX-U if the injection angle is shifted below the midplane and aimed towards the tophalf of the vacuum vessel. However, collisional damping of the EBW is projected to be significant, insome cases accounting for up to 97% of the absorbed EBW power« less

Creator(s)/Author(s):
;
Publication Date:
DOE Contract Number:  
AC02-09CH11466
Product Type:
Dataset
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
U. S. Department of Energy
Keywords:
Electron cyclotron; Startup; Spherical Tokamak; Electron Bernstein wave
OSTI Identifier:
1562054
DOI:
10.11578/1562054

Citation Formats

Lopez, N, and Poli, F. Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U. United States: N. p., 2018. Web. doi:10.11578/1562054.
Lopez, N, & Poli, F. Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U. United States. doi:10.11578/1562054.
Lopez, N, and Poli, F. 2018. "Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U". United States. doi:10.11578/1562054. https://www.osti.gov/servlets/purl/1562054. Pub date:Fri Jun 01 00:00:00 EDT 2018
@article{osti_1562054,
title = {Regarding the optimization of O1-mode ECRH and the feasibility of EBW startup on NSTX-U},
author = {Lopez, N and Poli, F},
abstractNote = {Recently published scenarios for fully non-inductive startup and operation on the National SphericalTorus eXperiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015) show ElectronCyclotron Resonance Heating (ECRH) as an important component in preparing a target plasma forefficient High Harmonic Fast Wave and Neutral Beam heating. The modeling of the propagation andabsorption of EC waves in the evolving plasma is required to define the most effective window ofoperation, and to optimize the launcher geometry for maximal heating and current drive during thiswindow. Here, we extend a previous optimization of O1-mode ECRH on NSTX-U to account for thefull time-dependent performance of the ECRH using simulations performed with TRANSP. We findthat the evolution of the density profile has a prominent role in the optimization by defining the timewindow of operation, which in certain cases may be a more important metric to compare launcherperformance than the average power absorption. This feature cannot be captured by analysis on staticprofiles, and should be accounted for when optimizing ECRH on any device that operates near thecutoff density. Additionally, the utility of the electron Bernstein wave (EBW) in driving current andgenerating closed flux surfaces in the early startup phase has been demonstrated on a number ofdevices. Using standalone GENRAY simulations, we find that efficient EBW current drive ispossible on NSTX-U if the injection angle is shifted below the midplane and aimed towards the tophalf of the vacuum vessel. However, collisional damping of the EBW is projected to be significant, insome cases accounting for up to 97% of the absorbed EBW power},
doi = {10.11578/1562054},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2018},
month = {6}
}

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