Magnetic shear effect on plasma transport at T e/T i ~ 1 through electron cyclotron heating in DIII-D plasmas

Yoshida, M.; McKee, G. R.; Petty, C. C.; Grierson, B. A.; Nakata, M.; Rost, C.; Rhodes, T. L.; Ernst, D. R.; Garofalo, A. M.

doi:10.1088/1741-4326/abbfe7

Title: Magnetic shear effect on plasma transport at T _e/T _i ~ 1 through electron cyclotron heating in DIII-D plasmas

Journal Article · Mon Nov 23 00:00:00 EST 2020 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/abbfe7· OSTI ID:1755224

Yoshida, M. ^[1]; McKee, G. R. ^[2];

^[3];

^[4];

^[5]; Rost, C. ^[6]; Rhodes, T. L. ^[7]; Ernst, D. R. ^[6];

^[3]

National Inst. for Quantum and Radiological Science and Technology, Ibaraki (Japan)
Univ. of Wisconsin, Madison, WI (United States)
General Atomics, San Diego, CA (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
National Inst. of for Fusion Sciences, Gifu (Japan)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Univ. of California, Los Angeles, CA (United States)

The effect of magnetic shear on plasma transport for an electron to ion temperature ratio (T _e/T _i) near unity has been explored in DIII-D utilizing electron cyclotron heating (ECH). Previous reports showed that significant confinement degradation occurred at T _e/T _i ~ 1 in positive shear (PS) plasmas in DIII-D, whereas reduced confinement degradation was observed in negative central shear (NCS) plasmas. In this study, plasma transport in weak magnetic shear (WS) plasmas with ECH is investigated and compared with that in NCS and PS plasmas. Here the magnetic shears ($$\hat s$$) are $$\hat s$$ > 0.5, ~0 and <-0.1 in the core region (ρ~ 0.3–0.4) of PS, WS and NCS plasmas, respectively, and flat or negative inside ρ~ 0.4 in the WS and NCS plasmas. Weak magnetic shear is found to be effective in minimizing degradation of ion thermal confinement as T _e/T _i increases through ECH application, and an improved confinement factor of H_98y2 ~ 1.2 is maintained, similar to NCS plasmas. At T _e/T _i ~ 1, the ion thermal diffusivity around an internal transport barrier decreases when changing the magnetic shear from positive to weak or negative shear. Also, reduced local particle and momentum transport was indicated by steeper density and toroidal rotation profiles in the weak and negative shear regimes. Linear gyrokinetic simulations predict little change in growth rates of low-k turbulence with ECH application in the WS and NCS plasmas, which is consistent with the transport and profile analyses.

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Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: FC02-04ER54698; FG02-08ER54999; AC02-09CH11466; FG02-08ER54984; SC0016154

OSTI ID:: 1755224

Journal Information:: Nuclear Fusion, Vol. 61, Issue 1; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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