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Title: Evidence and modeling of turbulence bifurcation in L-mode confinement transitions on Alcator C-Mod

Abstract

Analysis and modeling of rotation reversal hysteresis experiments show that a single turbulent bifurcation is responsible for the Linear to Saturated Ohmic Confinement (LOC/SOC) transition and concomitant intrinsic rotation reversal on Alcator C-Mod. Plasmas on either side of the reversal exhibit different toroidal rotation profiles and therefore different turbulence characteristics despite the profiles of density and temperature, which are indistinguishable within measurement uncertainty. Elements of this bifurcation are also shown to persist for auxiliary heated L-modes. The deactivation of subdominant (in the linear growth rate and contribution to heat transport) ion temperature gradient and trapped electron mode instabilities is identified as the only possible change in turbulence within a reduced quasilinear transport model across the reversal, which is consistent with the measured profiles and inferred heat and particle fluxes. Experimental constraints on a possible change from strong to weak turbulence, outside the description of the quasilinear model, are also discussed. These results indicate an explanation for the LOC/SOC transition that provides a mechanism for the hysteresis through the dynamics of subdominant modes and changes in their relative populations and does not involve a change in the most linearly unstable ion-scale drift-wave instability.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [1]; ORCiD logo [1];  [1]; ORCiD logo [1];  [1]; ORCiD logo [3]; ORCiD logo [1]
  1. Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
  2. University of California San Diego, San Diego, California 92093, USA
  3. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
Publication Date:
Research Org.:
Univ. of California, San Diego, CA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Contributing Org.:
Alcator C-Mod Team
OSTI Identifier:
1618845
Alternate Identifier(s):
OSTI ID: 1618588
Grant/Contract Number:  
FG02-04ER54738; SC0014264; FC02-99ER54512
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 27; Journal Issue: 5; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; hysteresis; modeling; turbulence; turbulent bifurcation; Alcator C-Mod; plasma; plasma physics; ion temperature gradient; instabilities

Citation Formats

Cao, N. M., Rice, J. E., Diamond, P. H., White, A. E., Chilenski, M. A., Ennever, P. C., Hughes, J. W., Irby, J., Reinke, M. L., and Rodriguez-Fernandez, P. Evidence and modeling of turbulence bifurcation in L-mode confinement transitions on Alcator C-Mod. United States: N. p., 2020. Web. doi:10.1063/1.5144444.
Cao, N. M., Rice, J. E., Diamond, P. H., White, A. E., Chilenski, M. A., Ennever, P. C., Hughes, J. W., Irby, J., Reinke, M. L., & Rodriguez-Fernandez, P. Evidence and modeling of turbulence bifurcation in L-mode confinement transitions on Alcator C-Mod. United States. doi:https://doi.org/10.1063/1.5144444
Cao, N. M., Rice, J. E., Diamond, P. H., White, A. E., Chilenski, M. A., Ennever, P. C., Hughes, J. W., Irby, J., Reinke, M. L., and Rodriguez-Fernandez, P. Thu . "Evidence and modeling of turbulence bifurcation in L-mode confinement transitions on Alcator C-Mod". United States. doi:https://doi.org/10.1063/1.5144444. https://www.osti.gov/servlets/purl/1618845.
@article{osti_1618845,
title = {Evidence and modeling of turbulence bifurcation in L-mode confinement transitions on Alcator C-Mod},
author = {Cao, N. M. and Rice, J. E. and Diamond, P. H. and White, A. E. and Chilenski, M. A. and Ennever, P. C. and Hughes, J. W. and Irby, J. and Reinke, M. L. and Rodriguez-Fernandez, P.},
abstractNote = {Analysis and modeling of rotation reversal hysteresis experiments show that a single turbulent bifurcation is responsible for the Linear to Saturated Ohmic Confinement (LOC/SOC) transition and concomitant intrinsic rotation reversal on Alcator C-Mod. Plasmas on either side of the reversal exhibit different toroidal rotation profiles and therefore different turbulence characteristics despite the profiles of density and temperature, which are indistinguishable within measurement uncertainty. Elements of this bifurcation are also shown to persist for auxiliary heated L-modes. The deactivation of subdominant (in the linear growth rate and contribution to heat transport) ion temperature gradient and trapped electron mode instabilities is identified as the only possible change in turbulence within a reduced quasilinear transport model across the reversal, which is consistent with the measured profiles and inferred heat and particle fluxes. Experimental constraints on a possible change from strong to weak turbulence, outside the description of the quasilinear model, are also discussed. These results indicate an explanation for the LOC/SOC transition that provides a mechanism for the hysteresis through the dynamics of subdominant modes and changes in their relative populations and does not involve a change in the most linearly unstable ion-scale drift-wave instability.},
doi = {10.1063/1.5144444},
journal = {Physics of Plasmas},
number = 5,
volume = 27,
place = {United States},
year = {2020},
month = {5}
}

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