Plasma Rotation Induced by Directed Waves in the Ion-Cyclotron Range of Frequencies

Abstract

Changes of the toroidal plasma rotation induced by directed waves in the ion-cyclotron range of frequencies (ICRF) have been identified experimentally for the first time on the JET tokamak. The momentum carried by the waves is initially absorbed by fast resonating ions, which subsequently transfer it to the bulk plasma. Thus, the results provide evidence for the influence of ICRF heated fast ions on plasma rotation.

Observations of rotation in JET plasmas with electron heating by ion cyclotron resonance heating

“…The momentum input by directed waves has been predicted to affect the rotation, and evidence of this has been obtained previously by comparing plasmas heated with fast magnetosonic waves propagating in the co-and the counter-current directions with modelling [13]; the absorbed wave momentum and the change in the toroidal rotation was in agreement with simulations with the SELFO code [20,21]. However, there are changes in the rotation profiles that cannot adequately be modelled with existing heating codes.…”

“…• phasing (relative phasing of the four straps 0 − π/2 − π − 3π/2), which is consistent with absorption of the momentum of the wave [3,13]. The rotation profile for dipole heating is shown in figure 8 at I p = 2.4 MA, B 0 = 2.4 T, ICRF frequency f = 42 MHz, H concentration n H /n D = 0.03, and off axis heating with the cyclotron resonance intersecting the midplane at about r = 0.4 m on the high-field side.…”

“…It is therefore of interest to investigate alternative methods to generate rotation. Toroidal rotation of the plasma is often seen during ion cyclotron resonance heating (ICRH) even when the momentum inputs by the waves are negligible [1][2][3][4][5][6][7][8][9][10][11][12][13]. In general, the rotation is rather small and caused by several weak mechanisms that are not fully understood.…”

Observation of ion cyclotron range of frequencies mode conversion plasma flow drive on Alcator C-Mod

“…Fast magnetosonic waves (fast wave, or FW) were shown to directly drive toroidal rotation on JET [23], but the observed toroidal rotation was small. Us ICRF mode conversion (MC), some preliminary evidence of poloidal flow drive (≤ 1 km/s at 2 MW rf power) was observed between the mode conversion surface and ion cyclotron (IC) layer on TFTR [24], but no further experiment was conducted.…”

Ion cyclotron resonance heating with consistent finite orbit widths and anisotropic equilibria

“…We use the sign convention that a plus means co-current, a minus counter-current. The motivation is to check the RF-induced particle pinch, which has been observed and described, e.g., in [9,25,26]. Due to wave-particle interactions, one can show that we expect a net inward drift of resonant particles for co-current injection and a net outward drift for counter-current.…”