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Title: A predictive model for the tokamak density limit

Abstract

We reproduce the Greenwald density limit, in all tokamak experiments by using a phenomenologically correct model with parameters in the range of experiments. A simple model of equilibrium evolution and local power balance inside the island has been implemented to calculate the radiation-driven thermo-resistive tearing mode growth and explain the density limit. Strong destabilization of the tearing mode due to an imbalance of local Ohmic heating and radiative cooling in the island predicts the density limit within a few percent. Furthermore, we found the density limit and it is a local edge limit and weakly dependent on impurity densities. Our results are robust to a substantial variation in model parameters within the range of experiments.

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1]; ORCiD logo [1];  [1]; ORCiD logo [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1335462
Grant/Contract Number:
AC02-09CH11466; SC0004125
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 10; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; density limit; tearing mode; impurity radiation

Citation Formats

Teng, Q., Brennan, D. P., Delgado-Aparicio, L., Gates, D. A., Swerdlow, J., and White, R. B. A predictive model for the tokamak density limit. United States: N. p., 2016. Web. doi:10.1088/0029-5515/56/10/106001.
Teng, Q., Brennan, D. P., Delgado-Aparicio, L., Gates, D. A., Swerdlow, J., & White, R. B. A predictive model for the tokamak density limit. United States. doi:10.1088/0029-5515/56/10/106001.
Teng, Q., Brennan, D. P., Delgado-Aparicio, L., Gates, D. A., Swerdlow, J., and White, R. B. 2016. "A predictive model for the tokamak density limit". United States. doi:10.1088/0029-5515/56/10/106001. https://www.osti.gov/servlets/purl/1335462.
@article{osti_1335462,
title = {A predictive model for the tokamak density limit},
author = {Teng, Q. and Brennan, D. P. and Delgado-Aparicio, L. and Gates, D. A. and Swerdlow, J. and White, R. B.},
abstractNote = {We reproduce the Greenwald density limit, in all tokamak experiments by using a phenomenologically correct model with parameters in the range of experiments. A simple model of equilibrium evolution and local power balance inside the island has been implemented to calculate the radiation-driven thermo-resistive tearing mode growth and explain the density limit. Strong destabilization of the tearing mode due to an imbalance of local Ohmic heating and radiative cooling in the island predicts the density limit within a few percent. Furthermore, we found the density limit and it is a local edge limit and weakly dependent on impurity densities. Our results are robust to a substantial variation in model parameters within the range of experiments.},
doi = {10.1088/0029-5515/56/10/106001},
journal = {Nuclear Fusion},
number = 10,
volume = 56,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
Free Publicly Available Full Text
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  • Several series of model problem calculations have been performed to investigate the predicted effect of pumping, divertor configuration and fueling on the maximum achievable density in diverted tokamaks. Density limitations due to thermal instabilities (confinement degradation and multifaceted axisymmetric radiation from the edge) and to divertor choking are considered. For gas fueling the maximum achievable density is relatively insensitive to pumping (on or off), to the divertor configuration (open or closed), or to the location of the gas injection, although the gas fueling rate required to achieve this maximum achievable density is quite sensitive to these choices. Thermal instabilities aremore » predicted to limit the density at lower values than divertor choking. Higher-density limits are predicted for pellet injection than for gas fueling.« less
  • A drift wave transport model, recently developed by Ottaviani, Horton and Erba (OHE) [Ottaviani {ital et al.}, Plasma Phys. Controlled Fusion {bold 39}, 1461 (1997)], has been implemented and tested in a time-dependent predictive transport code. This OHE model assumes that anomalous transport is due to turbulence driven by ion temperature gradients and that the fully developed turbulence will extend into linearly stable regions, as described in the reference cited above. A multiplicative elongation factor is introduced in the OHE model and simulations are carried out for 12 discharges from major tokamak experiments, including both L- and H-modes (low- andmore » high-confinement modes) and both circular and elongated discharges. Good agreement is found between the OHE model predictions and experiment. This OHE model is also used to describe the performance of the International Thermonuclear Experimental Reactor (ITER) [Putvinski {ital et al.}, in {ital Proceedings of the 16th IAEA Fusion Energy Conference}, Montr{acute e}al, Canada, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 2, p. 737.] A second version of the OHE model, in which the turbulent transport is not allowed to penetrate into linearly stable regions, has also been implemented and tested. In simulations utilizing this version of the model, the linear stability of the plasma core eliminates the anomalous thermal transport near the magnetic axis, resulting in an increase in the core temperatures to well above the experimental values. {copyright} {ital 1998 American Institute of Physics.}« less
  • The stabilization of both the ({ital m}=2, {ital n}=1) tearing mode and a detached plasma has been obtained with the use of the ergodic divertor in Tore Supra Ohmically heated discharges at the density limit and for low plasma pressure. This has allowed us, for the first time, to define and to check a discharge piloting strategy to prevent density-limit disruptions and to create a stable edge-radiating layer that dissipates 100% of the input power.
  • A Comment on the Letter by D. L. Brower {ital et} {ital al}., Phys. Rev. Lett. 67, 200 (1991).