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Title: Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas

We demonstrated negative magnetic shear in DIII-D and JT-60U in order to mitigate the confinement degradation typically observed with increasing the electron to ion temperature ratio (T-e/T-i). In recent experiments in DIII-D negative central magnetic shear (NCS) discharges, the thermal transport in the internal transport barrier formed around the radius of the minimum safety factor (q(min)) remained almost constant and modestly increased in the region outside of q(min) compared to the positive shear (PS) case, when T-e/T-i increased from about 0.8 to 1.1 through electron cyclotron heating (ECH). The benefit of NCS extending into the region outside of qmin can be explained by the lower magnetic shear in the NCS plasma over the plasma radius relative to the PS plasma. Reduced confinement degradation at high T-e/T-i with NCS plasmas was commonly observed in DIII-D and JT-60U. Furthermore, the mechanism of the different transport responses between the NCS and PS plasmas has been assessed in terms of fluctuation measurements and gyrokinetic simulations in DIII-D; NCS gave a smaller rise in the low-wavenumber broadband turbulent fluctuations with the increase in T-e/T-i compared with the PS case. This is consistent with gyrokinetic simulations, and this shows a smaller rise in the growth ratesmore » of the ion temperature gradient mode in the NCS plasmas, with increasing T-e/T-i. Gyrokinetic simulations also showed a change in the stability of the electron modes with ECH applied, consistent with higher-wavenumber fluctuation measurements, although more detailed simulations are needed to give a quantitative explanation for the experimental observations. Control of q-profile and magnetic shear will allow confinement improvement in future machines with dominant electron heating.« less
 [1] ;  [2] ;  [3] ; ORCiD logo [4] ;  [5] ;  [6] ;  [6] ;  [7] ;  [8] ;  [8] ;  [8] ;  [9] ;  [9] ;  [10] ;  [9] ;  [11] ;  [9] ; ORCiD logo [4]
  1. National Inst. for Quantum and Radiological Science and Technology, Ibaraki (Japan)
  2. Univ. of Wisconsin, Madison, WI (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. National Inst. for Fusion Sciences, Toki (Japan)
  6. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  7. Graduate Univ. for Advanced Studies (SOKENDAI), Toki (Japan)
  8. Univ. of California, Los Angeles, CA (United States)
  9. General Atomics, San Diego, CA (United States)
  10. Columbia Univ., New York, NY (United States)
  11. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Grant/Contract Number:
FG02-08ER54999; FG02-94ER54084; FG02-08ER54984; AC05-00OR22725; 16K06947; FG02-04ER54761; AC52-07NA27344; FC02-04ER54698; AC02-09C11466
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 5; Journal ID: ISSN 0029-5515
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); USDOE Office of Nuclear Energy (NE)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; thermal transport; electron heating; magnetic shear; rotation shear; asdex upgrade; d discharges; barriers; confinement; weak
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1374821; OSTI ID: 1374874