Speaker
Dr
Amanda Hubbard
(Massachusetts Institute of Technology, Plasma Science and Fusion Center)
Description
Significant progress has been made on Alcator C-Mod in expanding the configurations and conditions for which the I-mode regime can be accessed and maintained and understanding the physics which underlies the transport improvement. An important result from multidevice studies is that the power threshold for I-mode has only a weak dependence on BT, while the upper power limit increases with BT, making I-modes more robust at higher field [1]. Experiments in 2015 have extended this trend, achieving clear I-modes at up to 8.0 T. The I-mode regime is naturally stable to ELMs, and combines high tauE with low particle confinement [2]. This has benefits for fusion reactors, eliminating damaging ELM heat pulses and avoiding impurity accumulation.
TauE in I-mode is in the H-mode range and has weak power degradation ~P-0.3. ELITE analysis shows the pedestal to be stable, consistent with this lack of saturation and the absence of ELMs. Nonlinear GYRO simulations show that I-mode core Ti and Te profiles are stiffer than in L-mode, resembling H-mode with regards to marginal ITG stability. I-mode pedestal physics is also advancing, through measurements of fluctuations and flows and using simulations. Both a GAM and a high frequency fluctuation termed the Weakly Coherent Mode are present and strongly interact. Nonlinear BOUT++ simulations agree with many observed features of the WCM.
The C-Mod team has been exploring prospects for extrapolation of I-mode to larger fusion devices. We predict ITER would need about 70 MW to enter I-mode. It should be possible to remain in I-mode and to produce high fusion power, provided that density can be sufficiently increased. Accessibility for compact, high B fusion reactors such as ARC is even more favorable. We are also investigating integration with divertor solutions. Mitigating heat flux using low-Z impurity seeding has been demonstrated, and we have begun to investigate divertor detachment strategies. While robust I-mode operation is typically achieved with ion B×B drift away from the X-point, new experiments show that after the L-I transition, the regime can be maintained in a DN configuration. This may help to reduce peak heat flux. Further I-mode experiments will be a priority in the 2016 campaign.
[1] HUBBARD, A.E. et al, IAEA FEC 2014. [2] WHYTE, D. G., et al, Nucl. Fus. 50 (2010).
Work supported by U.S. DoE.
| Country or International Organization | USA |
|---|---|
| Paper Number | EX/3-1 |
Primary author
Dr
Amanda Hubbard
(Massachusetts Institute of Technology, Plasma Science and Fusion Center)
Co-authors
Prof.
Anne White
(Massachusetts Inst of Tech, Plasma Science and Fusion Center)
Mr
Brandon Sorbom
(Massachusetts Inst of Technology, Plasma Science and Fusion Center)
Dr
Brian LaBombard
(MIT Plasma Science and Fusion Center)
Dr
Dan Brunner
(MIT PSFC)
Prof.
Dennis Whyte
(MIT Plasma Science Fusion Center)
Dr
Earl Marmar
(Mass. Inst. of Technology)
Dr
Eric Edlund
(Massachusetts Institute of Technology)
Dr
Istvan Cziegler
(York Plasma Institute, University of York)
Dr
James Terry
(MIT-PSFC)
Jerry Hughes
(MIT PSFC)
Dr
John Rice
(MIT PSFC)
Dr
John Walk
(Massachusetts Inst of Technology, Plasma Science and Fusion Center)
Dr
Matthew Reinke
(Oak Ridge National Laboratory)
Dr
Stephen Wolfe
(Massachusetts Inst of Tech, Plasma Science and Fusion Center)
Stephen Wukitch
(MIT PSFC)
Xueqiao Xu
(Lawrence Livermore National Laboratory)
Dr
Yijun Lin
(MIT Plasma Science and Fusion Center)
Dr
Zixi Liu
(Institute of Plasma Physics, Chinese Academy of Sciences)
