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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

Abstract

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

Authors:
 [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:
Research Org.:
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 Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE National Nuclear Security Administration (NNSA); USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1353408
Alternate Identifier(s):
OSTI ID: 1374821; OSTI ID: 1374874; OSTI ID: 1779585
Report Number(s):
LLNL-JRNL-752082
Journal ID: ISSN 0029-5515
Grant/Contract Number:  
FG02-08ER54999; FG02-94ER54084; FG02-08ER54984; AC05-00OR22725; 16K06947; FG02-04ER54761; AC52-07NA27344; FC02-04ER54698; AC02-09C11466
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 5; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; thermal transport; electron heating; magnetic shear; rotation shear; asdex upgrade; d discharges; barriers; confinement; weak

Citation Formats

Yoshida, Maiko, McKee, George R., Murakami, Masanori, Grierson, Brian A., Nakata, M., Davis, Evan M., Marinoni, Alessandro, Ono, Makoto, Rhodes, Terry L., Sung, Choongki, Schmitz, Lothar, Petty, Craig C., Ferron, John R., Turco, Francesca, Garofalo, Andrea M., Holcomb, Christopher T., Collins, Cami M., and Solomon, Wayne M.. Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas. United States: N. p., 2017. Web. https://doi.org/10.1088/1741-4326/aa611e.
Yoshida, Maiko, McKee, George R., Murakami, Masanori, Grierson, Brian A., Nakata, M., Davis, Evan M., Marinoni, Alessandro, Ono, Makoto, Rhodes, Terry L., Sung, Choongki, Schmitz, Lothar, Petty, Craig C., Ferron, John R., Turco, Francesca, Garofalo, Andrea M., Holcomb, Christopher T., Collins, Cami M., & Solomon, Wayne M.. Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas. United States. https://doi.org/10.1088/1741-4326/aa611e
Yoshida, Maiko, McKee, George R., Murakami, Masanori, Grierson, Brian A., Nakata, M., Davis, Evan M., Marinoni, Alessandro, Ono, Makoto, Rhodes, Terry L., Sung, Choongki, Schmitz, Lothar, Petty, Craig C., Ferron, John R., Turco, Francesca, Garofalo, Andrea M., Holcomb, Christopher T., Collins, Cami M., and Solomon, Wayne M.. Thu . "Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas". United States. https://doi.org/10.1088/1741-4326/aa611e. https://www.osti.gov/servlets/purl/1353408.
@article{osti_1353408,
title = {Magnetic shear effects on plasma transport and turbulence at high electron to ion temperature ratio in DIII-D and JT-60U plasmas},
author = {Yoshida, Maiko and McKee, George R. and Murakami, Masanori and Grierson, Brian A. and Nakata, M. and Davis, Evan M. and Marinoni, Alessandro and Ono, Makoto and Rhodes, Terry L. and Sung, Choongki and Schmitz, Lothar and Petty, Craig C. and Ferron, John R. and Turco, Francesca and Garofalo, Andrea M. and Holcomb, Christopher T. and Collins, Cami M. and Solomon, Wayne M.},
abstractNote = {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.},
doi = {10.1088/1741-4326/aa611e},
journal = {Nuclear Fusion},
number = 5,
volume = 57,
place = {United States},
year = {2017},
month = {3}
}

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