Spontaneous Toroidal Rotation, Flow Reversal, and Flow Sustainment inNon-Inductive Steady State Tokamak Plasma on QUEST
H. Zushi, K. Mishra a, T. Onchi, A. Kuzmin, H. Idei and the QUEST Group
Advanced Fusion Research Center, RIAM Kyushu University,6-1 Kasuga, 816-8560, Japana
AEES Kyushu University,6-1 Kasuga, 816-8560, Japanzushi@triam.kyushu-u.ac.jp

Intrinsic toroidal rotation Vin fully non-inductive tokamak plasma driven by electron
cyclotron waves(ECW) has been investigated. Doppler shift of line emissions from intrinsic
impurities (CIII) and bulk ions (HeII) have been measured with a visible spectroscopy attachedwith a 25 channel fiber array viewing a plasma tangentially on the mid-plane. ECWs at 8.2GHz(<100kW) are injected from the low field side and are used to start-up and drive thenon-inductive plasma current [1]. In this paper rotation measurements performed in a plasma,characterized by the natural divertor configuration with an inboard polloidal field null (IPN),
will be presented. Typical plasma parameters are as follows; line density < 0.1-1.2 ×1018m-2,
Te ~ 50- 600 eV, Ip~10- 20 kA, Bt0=0.14T at R=0.6m, and p~1. Since the vertical fieldBz(~10 % of Bt) was kept constant during the start-up and whole plasma duration, Ware pinch
mechanism is excluded and there is no external momentum input. In order to interpret theobserved line of sight profile <Va Gauss fitting procedure is used for the spectrum
integrated the local Gaussian spectra locally determined by emissivity(intensity), Vshift,and ion temperature(width) along a line of sight.
Spontaneous toroidal rotation V was clearly found during the current ramping-up phase(Ip~1-2 kA), namely in the open magnetic field configuration. The direction of rotation is onlydetermined by the sign of Bz, which decides the direction of Ip. In this sense the rotation is in theco-current direction. The velocity increases with increasing Bz. In other magnetic
configurations, for example, ohmic induction plasma at high Bz/Bt >10 % and non-inductive
inboard limiter plasma at low Bz/Bt < 1 %, zero or small counter-current flow was seen.
Topological effects of the magnetic field configuration on acceleration mechanisms for ions inco-direction will be discussed.
Co-current toroidal angular frequency  (~30 krad/s) could be sustained during thewhole plasma duration. In order to investigate the flow reversal mechanisms with respect to thedensity, intense puff was injected from the inboard side towards the null point. As the density
increases up to 1.2 ×1018m-2 within 15 msec, it decays within 0.1 sec quickly and then 0.2-0.4
×1018m-2 is decreased gradually. During this phase the flow is reversed in the counter currentdirection near the inboard edge, but within 0.1-0.2 sec it is recovered in the co-direction. Basedon the details of (R,t)and SOL flows plausible mechanisms will be discussed.
It is an important task to sustain the intrinsic rotation in steady state. This wasdemonstrated in steady state IPN plasma lasting for 600 sec. The plasma current (~16 kA) anddensity 2 ×1017m-2could be feedback controlled by repetition of pulse puff to keep therecycling flux constant. It could be demonstrated that co-current <Vof 20 km/s near theplasma center and poloidal rotation of ~1km/s in the ion-diamagnetic direction are sustained.
The effects of particle fueling on the rotation profile will be discussed.
[1] S. Tashima, et al., Nucl. Fusion 54 (2014) 023010,