Physics Mechanisms of Toroidal Rotation Profile and Properties of Momentum Transport in JT-60U

Abstract

The roles of momentum transport on the toroidal rotation velocity (V t ) profile and the properties of transport coefficients are found by transient momentum transport analysis. The perturbation technique enables us to evaluate the momentum diffusivity (χ φ ) and the convection velocity (V conv ), and to calculate V t profiles driven by external torque input by neutral beams (NBs). The measured V t profiles with and without the external torque input are almost reproduced by χ φ and V conv in low-β (β N < 0.4) plasmas. At higher β, the local pressure gradient plays a role in determining the local value of intrinsic rotation velocity. Concerning the momentum transport, χ φ increases with increasing heating power, and decreases with increasing plasma current (I p ). In H-mode plasmas, χ φ is smaller than that in L-mode plasmas under similar experimental conditions. It is found that χ φ , which is separated from the non-diffusive term increases with increasing heat diffusivity (χ i ), χ φ /χ i ∼ 1-3, and −V conv increases with increasing χ φ , V conv /χ φ ∼ −2.5 to −0.7 m −1 , in H-mode plasmas.

Overview of JT-60U results towards the establishment of advanced tokamak operation

“…The ratio of V conv to χ φ is found to be −2 to −0.5 (m −1 ). The intrinsic rotation driven by the local pressure gradient towards the counter-direction increases with increasing the ion pressure gradient (grad P i ) [19,20]. This dependence is quite robust, since the same dependence is found in different plasma conditions (different I p , L-mode, H-mode, co-V T , counter-V T and no rotation), as shown in figure 16.…”

“…The measured V T in the region of 0.2 < r/a < 0.3 is changed with ECH to the co-direction, while that in the region 0.3 < r/a < 0.6 changed to the counter-direction [20]. This response of V T to ECH is determined by the combination of the momentum transport, the intrinsic rotation by grad P i and the intrinsic rotation by ECH.…”

“…Yokokura, H. Yoshida 5 , Maiko Yoshida, Masafumi Yoshida 19 , N. Yoshida 19 , Z. Yoshida 20 , A. Yoshikawa 23 , J. Zhao 8 , H. Zohm 16 and H. Zushi 19 Japan Atomic Energy Agency 1 Post-Doctoral Fellow 2 Tohoku University, Japan 3 Consorzio RFX 4 National Institute for Fusion Science, Japan 5 Osaka University, Japan 6 Tomsk Polytechnic University, Russia 7 National Nuclear Center Republic of Kazakhstan 8 Institute of Plasma Physics, Chinese Academy of Sciences, China 9 Kyoto University, Japan 10 Staff on loan 11 General Atomics, USA 12 Princeton Plasma Physics Laboratory, USA 13 University of Tsukuba, Japan 14 Hokkaido University, Japan 15 National Institute of Advanced Industrial Science and Technology, Japan 16 Max-Planck-Institut für Plasmaphysik, Germany 17 Australian National University, Australia 18 Tokyo Institute of Technology, Japan 19 Kyushu University, Japan 20 The University of Tokyo, Japan 21 Association EURATOM-CEA 22 Hiroshima Institute of Technology, Japan 23 Shizuoka University, Japan 24 Nagoya University, Japan 25 Euratom/UKAEA Association, UK 26 Kanazawa University, Japan…”

Conference summary: progress in experiments on innovative concepts, confinement and performance

“…Pedestal parameters and confinement have been shown to be improved with co-rotation following the installation of ferritic steel tiles in JT-60U (see also section 4.1), and fast ion losses due to toroidal field ripple are found to induce toroidal rotation in the direction anti-parallel to the plasma current (counter rotation) [24]. The reduction of the radial electric field attributed to the decrease in the fast ion loss with the ferritic steel tiles is believed to slow down the ctr-rotation at the plasma edge, thus enhancing co-rotation and leading to improved energy confinement [25].…”

“…using the F3D OFMC code indicate that the total absorbed power increases by ∼30% at B T < 2 T for the large volume configuration close to the wall, which had so far suffered from the large toroidal field ripple [23], leading to smaller required neutral beam (NB) units for a given normalized beta, β N = β/(I p /aB), better flexibility in neutral beam injection (NBI) combination and better flexibility of the torque profile. In addition, the effects of the installation of the ferritic steel tiles on toroidal rotation and confinement have been clearly observed [24,25]. The reduction of the radial electric field attributed to the decrease in the fast ion loss with the ferritic steel tiles is believed to slow down the ctr-rotation at the plasma edge which so far was characteristic of JT-60U (see also section 4.5.1).…”