Electron cyclotron heating and core intrinsic rotation reversal in DIII-D

Abstract

Abstract. The effect of electron cyclotron heating (ECH) on the intrinsic rotation profile in DIII-D is shown experimentally. Former DIII-D experiments have shown that ECH tends to cause an interior reduction in the normally co-Ip directed intrinsic rotation profile, and this core rotation can be fully reversed to the opposite direction. This effect is due to a turbulent rearrangement of the interior rotation profile. Here, we show results that there is more than one mechanism causing this. We compare two low density L-mode discharges where the only operational difference is the location of the ECH deposition. At low ECH power, comparable to the Ohmic power, the primary change is in the q-profile accompanied by a reversal of the core intrinsic rotation direction for the more off-axis deposition. The change in the shear of the q-profile fits well with a recent theoretical prediction for this rotation reversal. At higher ECH power, the primary change is in the core electron temperature, Te, accompanied by a hollowing of the rotation profile near the magnetic axis. This effect appears to be due to the change in electron collisionality, consistent with another theoretical, gyrokinetic prediction. The variety of phenomena that could allow ECH to modify the intrinsic rotation profile give some expectation that regions of large velocity shear in the interior could be generated, with the possibility of triggering internal transport barriers.

Experimental observations of driven and intrinsic rotation in tokamak plasmas

“…A common observation is that ECH H-modes exhibit co-current toroidal rotation in the edge regions [205,206,234] and a scaling with stored energy [206] similar to that seen in Ohmic (section 5.1.1) and ICRF (section 5.1.2) enhanced confinement plasmas [229]. A different characteristic feature of some ECH H-mode plasmas is the counter-current toroidal rotation observed in the core regions [205,206,236], an effect which depends on the ECH power deposition location. Off-axis power deposition leads to cocurrent rotation in the core [206].…”

“…Modifications to the velocity profile due to changes in the q profile through ECH resonance location scans have been observed in DIII-D L-mode plasmas [236]. Rotation changes due to induced magnetic islands have been documented in J-TEXT discharges [164], and the effects of sawteeth on the velocity profile have been described for TCV plasmas [259], indicating other manifestations of q profile effects.…”

“…The toroidal rotation profile has been examined in L-mode target discharges with ECH [205,206,230,[233][234][235][236], some of which entered H-mode. A common observation is that ECH H-modes exhibit co-current toroidal rotation in the edge regions [205,206,234] and a scaling with stored energy [206] similar to that seen in Ohmic (section 5.1.1) and ICRF (section 5.1.2) enhanced confinement plasmas [229].…”

“…For co-rotating NBI plasmas, addition of ECH leads to a countercur rent velocity increment while in counter-rotating NBI target plasmas the velocity change is in the co-current direction [235]. Another important variable in determining the rotation response to ECH is the effect of the q profile [236,241].…”