On the toroidal plasma rotations induced by lower hybrid waves

Guan, Xiaoying; Qin, Hong; Liu, Jian; Fisch, Nathaniel J.

doi:10.1063/1.4791666

Cited by 16 publications

(10 citation statements)

References 40 publications

(45 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In fact initially there was some confu sion in the interpretation of results with LHCD since rotation was observed to change in both the cocurrent [12,[23][24][25][26][27] and countercurrent [27][28][29] directions. A large number of mech anisms has been proposed to explain the rotation changes in plasmas with LH wave injection, including: direct momentum input from LH waves [12,30], electron orbit loss [23,25], the trapped electron pinch [31], resonant electron radial drifts [32,33], the turbulent equipartition pinch [26] and the effects of magnetic shear on the turbulence spectrum [34,35]. It's likely that there is a simultaneous contribution from many of these effects, and the competition can lead to a rotation reversal.…”

Section: Introductionmentioning

confidence: 99%

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

Rice¹,

Gao²,

Mumgaard³

et al. 2016

Nucl. Fusion

View full text Add to dashboard Cite

Changes in the core toroidal rotation profiles following injection of lower hybrid (LH) waves have been documented in Alcator C-Mod plasmas. Shot by shot scans of LH input power have been performed at fixed magnetic field and electron density for several plasma currents. For sawtoothing target plasmas, if the input power is low enough that the central safety factor q0 remains below 1, the change in the core rotation is in the countercurrent direction, consistent in sign, magnitude and LH power scaling with direct momentum input from the LH waves. If the power level is high enough that there are significant changes to the q profile, including the termination of sawtooth oscillations, the change in the toroidal rotation is in the co-current direction, consistent with changes in the momentum flux through its dependence on the current density profile. The direction of the rotation changes depends on the whether q0 is below or above unity, and seemingly not on the magnetic shear, nor the Ohmic confinement regime of the target plasma.

show abstract

Section: Introductionmentioning

confidence: 99%

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

Rice¹,

Gao²,

Mumgaard³

et al. 2016

Nucl. Fusion

View full text Add to dashboard Cite

show abstract

“…In plasmas with good core absorption of LH waves, the mechanism for rotation drive is uncertain. Candidates include direct momentum input from the waves [19] (calculated to be low [8]), electron orbit loss [12,14], trapped electron pinch effects [20], resonant electron radial drift [21,22], and less direct causes such as the turbulent equipartition pinch [17] or modification of the q profile. A challenge of these accounts is to explain the direction of the change in rotation.…”

Section: Introductionmentioning

confidence: 99%

Effects of LHRF on toroidal rotation in Alcator C-Mod plasmas

Rice¹,

Podpaly²,

Reinke³

et al. 2013

Nucl. Fusion

View full text Add to dashboard Cite

Application of lower hybrid range of frequencies (LHRF) waves can induce both co-and counter-current directed changes in toroidal rotation in Alcator C-Mod plasmas, depending on the target plasma current, electron density, confinement regime and magnetic shear. For ohmic L-mode discharges with good core LH wave absorption, and significant current drive at a fixed LH power near 0.8 MW, the interior (r/a < 0.5) rotation increments (on a time scale of order the current relaxation time) in the counter-current direction if n e (10 20 m −3) > q 95 /11.5, and in the co-current direction if n e (10 20 m −3) < q 95 /11.5. All discharges with co-current rotation changes have q 0 > 1, indicating a good correlation with driven current fraction, unifying the results observed on various tokamaks. For high density (n e 1.2 × 10 20 m −3) L-mode target discharges, where core LH wave absorption is low, the rotation change is in the co-current direction, but evolves on a shorter momentum transport time scale, and is seen across the entire spatial profile. For H-mode target plasmas, both co-and counter-current direction increments have been observed with LHRF. The H-mode co-rotation is correlated with the pedestal temperature gradient, which itself is enhanced by the LH waves absorbed in the plasma periphery. The H-mode counter-rotation increment, a flattening of the peaked velocity profile in the core, is consistent with a reduction in the momentum pinch correlated with a steepening of the core density profile. Most of these rotation changes must be due to indirect transport effects of LH waves on various parameters, which modify the momentum flux.

show abstract

“…In the parallel direction, there is also a net transfer of momentum equal to hk z times the number of quanta absorbed per unit time (F = k P/ω), but this momentum is passed to the bulk ions on a collisional time scale only. In the perpendicular direction, the momentum is passed to the bulk ions almost instantaneously, on the cyclotron timescale 24,25 (see also appendix A). In this paper, we neglect the force in the parallel direction anyway.…”

Section: Theoretical Framework a Wave Forcing And Ion Momentum Equationmentioning

confidence: 99%

Impact of azimuthal forcing on the Brillouin limit in a collisional two-species Ohkawa filter

Nicolas

2022

Physics of Plasmas

View full text Add to dashboard Cite

This paper investigates the physics of plasma separation in a two species rotating collisional Ohkawa filter, when the source of rotation is an orbital angular momentum carrying wave. The electric field is treated self-consistently with ion and electron radial motion. The injection of angular momentum causes radial currents leading to charge penetration and electric field build up. The electric field varies until an equilibrium with the friction forces is reached. Both collisions with neutrals and Coulomb collisions are considered. In the case where the electric field is driven by the resonant wave, there is no collisional breakdown of the Brillouin limit [Rax et al., Phys. Plasmas 22, 092101 (2015)]; on the contrary, the maximum achievable electric field decreases when the collision frequency is increased. When two species are present, one that undergoes the wave forcing while the second does not interact with the wave, we find the following: the first species is confined, while the second species can be expelled or confined depending on the charge to mass ratio and the collisionalities. Assuming equal charge numbers, if the second species is the heavy one, it is always expelled, which is a standard result. When the second species is the light one, it can also be expelled in the common case where neutral collisions dominate over Coulomb collisions, which constitutes a new result.

show abstract

On the toroidal plasma rotations induced by lower hybrid waves

Cited by 16 publications

References 40 publications

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

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

Effects of LHRF on toroidal rotation in Alcator C-Mod plasmas

Impact of azimuthal forcing on the Brillouin limit in a collisional two-species Ohkawa filter

Contact Info

Product

Resources

About