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This content will become publicly available on May 1, 2019

Title: Transport barriers in bootstrap-driven tokamaks

Experiments have demonstrated improved energy confinement due to the spontaneous formation of an internal transport barrier in high bootstrap fraction discharges. Gyro kinetic analysis, and quasilinear predictive modeling, demonstrates that the observed transport barrier is caused by the suppression of turbulence primarily from the large Shafranov shift. It is shown, that the Shafranov shift can produce a bifurcation to improved confinement in regions of positive magnetic shear or a continuous reduction in transport for weak or negative magnetic shear. Operation at high safety factor lowers the pressure gradient threshold for the Shafranov shift driven barrier formation. Two self-organized states of the internal and edge transport barrier are observed. It is shown that these two states are controlled by the interaction of the bootstrap current with magnetic shear, and the kinetic ballooning mode instability boundary. Election scale energy transport is shown to be dominant in inner 60% of the profile. Energetic particle driven instabilities could also be playing a role in the thermal energy transport in this region.
Authors:
ORCiD logo [1] ;  [1] ; ORCiD logo [2] ;  [1] ;  [1] ; ORCiD logo [1]
  1. General Atomics, P.O. Box 85608, San Diego, California 92168-5608, USA
  2. Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
Publication Date:
Grant/Contract Number:
FC02-04ER54698; FG02-95ER54309
Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 5; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Research Org:
U.S. Department of Energy
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
OSTI Identifier:
1459670
Alternate Identifier(s):
OSTI ID: 1438969