Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

Journal Article · Mon May 04 00:00:00 UTC 2015 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.4919395 · OSTI ID:1253129

Lu, Z. X. ^[1]; Wang, W. X. ^[2]; Diamond, P. H. ^[3]; Tynan, G. ^[4]; Ethier, S. ^[2]; Gao, C. ^[5]; Rice, J. ^[6]

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1. Univ. of California, San Diego, CA (United States). Center for Energy Research, Department of Mechanical and Aerospace Engineering, Center for Momentum Transport and Flow Organization, and Center for Astrophysics and Science; OSTI
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
3. Univ. of California, San Diego, CA (United States). Center for Momentum Transport and Flow Organization and Center for Astrophysics and Space Science
4. Univ. of California, San Diego, CA (United States). Center for Energy Research, Department of Mechanical and Aerospace Engineering, Center for Momentum Transport and Flow Organization, and Center for Astrophysics and Science
5. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
6. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

We report that intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. Here we focus on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (sˆ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak sˆ . Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak sˆ discharges and that the value of sˆ _crit is consistent with the experimental results sˆ ^exp_crit [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. In conclusion, the consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive sˆ .

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States); Univ. of California, San Diego, CA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 1253129
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 22; ISSN PHPAEN; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English