Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas
[4];
[4]
- National Inst. for Quantum and Radiological Science and Technology, Ibaraki (Japan)
- Univ. of Wisconsin, Madison, WI (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
- National Inst. for Fusion Sciences, Toki (Japan)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Graduate Univ. for Advanced Studies (SOKENDAI), Toki (Japan)
- Univ. of California, Los Angeles, CA (United States)
- General Atomics, San Diego, CA (United States)
- Columbia Univ., New York, NY (United States)
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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 rates 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.
- Research Organization:
- Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE National Nuclear Security Administration (NNSA); USDOE Office of Nuclear Energy (NE)
- Grant/Contract Number:
- FG02-08ER54999; FG02-94ER54084; FG02-08ER54984; AC05-00OR22725; 16K06947; FG02-04ER54761; AC52-07NA27344; FC02-04ER54698; AC02-09C11466
- OSTI ID:
- 1353408
- Alternate ID(s):
- OSTI ID: 1374821; OSTI ID: 1374874; OSTI ID: 1779585
- Report Number(s):
- LLNL-JRNL-752082
- Journal Information:
- Nuclear Fusion, Vol. 57, Issue 5; ISSN 0029-5515
- Publisher:
- IOP ScienceCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Internal transport barrier in tokamak and helical plasmas
|
journal | January 2018 |
Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations
|
journal | February 2019 |
| Subdominant modes and optimization trends of DIII-D reverse magnetic shear configurations | text | January 2019 |
Similar Records
Physics of advanced tokamaks
Reduced electron thermal transport in low collisionality H-mode plasmas in DIII-D and the importance of TEM/ETG-scale turbulence