Effects of the q profile on toroidal rotation in Alcator C-Mod LHCD plasmas

Rice, J. E.; Gao, C.; Mumgaard, R.; Parker, R.R.; Scott, Steve; Shiraiwa, S.; Wallace, G.; Bonoli, P. T.; Delgado‐Aparicio, L.; Fenzi, C.; Granetz, R.; Greenwald, M.; Hubbard, A.; Hughes, J. W.; Irby, J.; Lee, J.P.; Marmar, E.; Reinke, M.L.; Wolfe, S.

doi:10.1088/0029-5515/56/3/036015

Cited by 14 publications

(10 citation statements)

References 50 publications

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“…Such a phenomenon differs from the observations in other NTM stabilization experiments by ECWs [12,14,33]. Although it is well known that the plasma rotation can be affected by ECRH or other RF wave heating [29][30][31], and the mode frequency can also be affected by the electromagnetic torque due to the eddy currents in the wall [35] and the NTV torque generated by the mode itself [34], the mechanism for the correlation between the frequency decrease and the island width reduction, as well as the observed threshold in the island width for the frequency decrease observed in our experiments, is not yet clear. As the stabilizing efficiency of ECRH/ECCD depends on the island rotation frequency [45,46], and the effect of RF wave heating on plasma rotation is also an important issue in fusion research, future study on the effect of local ECRH at the resonant surface on plasma rotation is still required to understand the underlying physics.…”

Section: Discussion and Summarycontrasting

confidence: 57%

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Tearing mode stabilization by electron cyclotron resonant heating in EAST tokamak experiments

et al. 2021

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Tearing mode stabilization by electron cyclotron waves (ECWs) has been carried out in Experimental advanced superconductiong tokamak (EAST) experiments. The effects of the amount of ECW power and the radial wave deposition location on stabilizing the m/n = 2/1 magnetic island are investigated, where m/n is the poloidal/toroidal mode number. The local heating is found to dominate the mode stabilization in these experiments. The stabilization is more effective when the wave is deposited closer to the radial island location, as expected. With increasing ECW power, however, the tearing modes are not stabilized completely, and the island width saturates at a finite width. Moreover, the island rotation frequency is found to decrease when the ECW deposition is close to the island such that the island width is reduced significantly. Using externally applied, rotating resonant magnetic perturbations to generate slowly rotating magnetic islands, the locked island stabilization by ECW has also been studied, and the island width reduction and nonuniform island rotation are observed when the island’s center passes through the ECW deposition region.

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Section: Discussion and Summarycontrasting

confidence: 57%

“…It is well known that RF heating can change the plasma rotation velocity [29][30][31], i.e. the so-called intrinsic torque [32].…”

Section: Effect Of the Ecw On Mode Rotationmentioning

confidence: 99%

Tearing mode stabilization by electron cyclotron resonant heating in EAST tokamak experiments

et al. 2021

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“…These force density profiles, which mainly show drive in the counter-current direction, are very similar to the LH power deposition profiles. Rotation in the counter-current direction [67][68][69][70][71][72][73] has been observed in LH experiments on C-Mod and Tore Supra. An example of direct rotation drive by LH waves is demonstrated in figure 4, which shows a shot by shot comparison of the time response of the core toroidal rotation velocity to LH wave injection at various power levels for Ohmic L-mode target plasmas in Alcator C-Mod [73].…”

Section: Lower Hybrid Wavesmentioning

confidence: 88%

Experimental observations of driven and intrinsic rotation in tokamak plasmas

Rice¹

2016

Plasma Phys. Control. Fusion

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Experimental observations of driven and intrinsic rotation in tokamak plasmas are reviewed. For momentum sources, there is direct drive from neutral beam injection, lower hybrid and ion cyclotron range of frequencies waves (including mode conversion flow drive), as well as indirect j B × forces from fast ion and electron orbit shifts, and toroidal magnetic field ripple loss. Counteracting rotation drive are sinks, such as from neutral drag and toroidal viscosity. Many of these observations are in agreement with the predictions of neo-classical theory while others are not, and some cases of intrinsic rotation remain puzzling. In contrast to particle and heat fluxes which depend on the relevant diffusivity and convection, there is an additional term in the momentum flux, the residual stress, which can act as the momentum source for intrinsic rotation. This term is independent of the velocity or its gradient, and its divergence constitutes an intrinsic torque. The residual stress, which ultimately responds to the underlying turbulence, depends on the confinement regime and is a complicated function of collisionality, plasma shape, and profiles of density, temperature, pressure and current density. This leads to the rich intrinsic rotation phenomenology. Future areas of study include integration of these many effects, advancement of quantitative explanations for intrinsic rotation and development of strategies for velocity profile control.

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“…The only obvious point here is that the q value and the magnetic shear would be smaller in the gradient region than those at the anchor point. Furthermore, it is not clear yet whether the q 95 dependence of the gradient region and the anchor point in Ohmic plasmas is related to the effects of the q profile investigated by using the injection of lower hybrid (LH) in Alcator C-Mod [33] or not.…”

Section: Analysis Of the Kstar Ohmic Plasma Databasementioning

confidence: 99%

A comprehensive study on rotation reversal in KSTAR: experimental observations and modelling

Angioni

et al. 2017

Nucl. Fusion

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Dedicated experiments have been performed in KSTAR Ohmic plasmas to investigate the detailed physics of the rotation reversal phenomena. Here we adapt the more general definition of rotation reversal, a large change of the intrinsic toroidal rotation gradient produced by minor changes in the control parameters (Camenen et al 2017 Plasma Phys. Control. Fusion 59 034001), which is commonly observed in KSTAR regardless of the operating conditions. The two main phenomenological features of the rotation reversal are the normalized toroidal rotation gradient () change in the gradient region and the existence of an anchor point. For the KSTAR Ohmic plasma database including the experiment results up to the 2016 experimental campaign, both features were investigated. First, the observations show that the locations of the gradient and the anchor point region are dependent on . Second, a strong dependence of on is clearly observed in the gradient region, whereas the dependence on , , and is unclear considering the usual variation of the normalized gradient length in KSTAR. The experimental observations were compared against several theoretical models. The rotation reversal might not occur due to the transition of the dominant turbulence from the trapped electron mode to the ion temperature gradient mode or the neoclassical equilibrium effect in KSTAR. Instead, it seems that the profile shearing effects associated with a finite ballooning tilting well reproduce the experimental observations of both the gradient region and the anchor point; the difference seems to be related to the magnetic shear and the value. Further analysis implies that the increase of in the gradient region with the increase of the collisionality would occur when the reduction of the momentum diffusivity is comparatively larger than the reduction of the residual stress. It is supported by the perturbative analysis of the experiments and the nonlinear gyrokinetic simulations. The absence of the sign change of even when a much lower collisionality is produced by additional electron cyclotron heating brings further experimental support to this interpretation.

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Effects of the q profile on toroidal rotation in Alcator C-Mod LHCD plasmas

Cited by 14 publications

References 50 publications

Tearing mode stabilization by electron cyclotron resonant heating in EAST tokamak experiments

Tearing mode stabilization by electron cyclotron resonant heating in EAST tokamak experiments

Experimental observations of driven and intrinsic rotation in tokamak plasmas

A comprehensive study on rotation reversal in KSTAR: experimental observations and modelling

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