2 Search Results

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 . Basedmore » 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 .« less

A double-focusing mass spectrograph has been used to photograph the doublets at mass number 25, 26, and 27 formed by doubly charged Cr⁵⁰, Cr⁵², Fe⁵⁴ and singly charged C₂H, C₂H₂, and C₂H₃. Typical C₂H₂—Cr⁵² and C₂H₃—Fe⁵⁴ doublets are shown in Fig. 1. The metallic ions were obtained from a high frequency spark between stainless steel electrodes. Finally, the method by which the hydrocarbon ions were obtained is described below.