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

Abstract

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 H98y2 ~ 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.

Authors:
 [1];  [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5];  [6];  [7];  [6]; ORCiD logo [3]
  1. National Inst. for Quantum and Radiological Science and Technology, Ibaraki (Japan)
  2. Univ. of Wisconsin, Madison, WI (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  5. National Inst. of for Fusion Sciences, Gifu (Japan)
  6. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  7. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1755224
Grant/Contract Number:  
FC02-04ER54698; FG02-08ER54999; AC02-09CH11466; FG02-08ER54984; SC0016154
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 61; Journal Issue: 1; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Yoshida, M., McKee, G. R., Petty, C. C., Grierson, B. A., Nakata, M., Rost, C., Rhodes, T. L., Ernst, D. R., and Garofalo, A. M.. Magnetic shear effect on plasma transport at T e/T i ~ 1 through electron cyclotron heating in DIII-D plasmas. United States: N. p., 2020. Web. https://doi.org/10.1088/1741-4326/abbfe7.
Yoshida, M., McKee, G. R., Petty, C. C., Grierson, B. A., Nakata, M., Rost, C., Rhodes, T. L., Ernst, D. R., & Garofalo, A. M.. Magnetic shear effect on plasma transport at T e/T i ~ 1 through electron cyclotron heating in DIII-D plasmas. United States. https://doi.org/10.1088/1741-4326/abbfe7
Yoshida, M., McKee, G. R., Petty, C. C., Grierson, B. A., Nakata, M., Rost, C., Rhodes, T. L., Ernst, D. R., and Garofalo, A. M.. Mon . "Magnetic shear effect on plasma transport at T e/T i ~ 1 through electron cyclotron heating in DIII-D plasmas". United States. https://doi.org/10.1088/1741-4326/abbfe7. https://www.osti.gov/servlets/purl/1755224.
@article{osti_1755224,
title = {Magnetic shear effect on plasma transport at T e/T i ~ 1 through electron cyclotron heating in DIII-D plasmas},
author = {Yoshida, M. and McKee, G. R. and Petty, C. C. and Grierson, B. A. and Nakata, M. and Rost, C. and Rhodes, T. L. and Ernst, D. R. and Garofalo, A. M.},
abstractNote = {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 H98y2 ~ 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.},
doi = {10.1088/1741-4326/abbfe7},
journal = {Nuclear Fusion},
number = 1,
volume = 61,
place = {United States},
year = {2020},
month = {11}
}

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