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

Abstract

Recent JT-60U experimental results towards the establishment of advanced tokamak (AT) operation are reviewed. We focused on the further expansion of the operational regime of AT plasmas towards higher βN regime with wall stabilization. After the installation of ferritic steel tiles in 2005, the high power heating in a large plasma cross-section in which the wall stabilization is expected has been possible. In 2007, the modification of power supply of NBIs improved the flexibility of the heating profile in long-pulse plasmas. The investigation of key physics issues for the establishment of steady-state AT operation is also in progress using new diagnostics and improved heating systems. In weak magnetic shear plasma, high βN ∼ 3 exceeding the ideal MHD limit without a conducting wall ( ) is sustained for ∼5 s (∼3τR) with RWM stabilization by a toroidal rotation at the q = 2 surface. External current drivers of negative-ion based NB and lower-hybrid waves together with a large bootstrap current fraction (f BS) of 0.5 can sustain the whole plasma current of 0.8 MA for 2 s (1.5τR). In reversed magnetic shear plasma, high βN ∼ 2.7 (βp ∼ 2.3) exceeding with q min ∼ 2.4 (q 95 ∼ 5.3), H H98(y,2) ∼ 1.7 and f BS ∼ 0.9 is obtained with wall stabilization. These plasma parameters almost satisfy the requirement of ITER steady-state scenario. In long-pulse plasmas with positive magnetic shear, a high βN H H98(y,2) of 2.6 with βN ∼ 2.6 and H H98(y,2) ∼ 1 is sustained for 25 s, significantly longer than the current diffusion time (∼14τR) without neoclassical tearing modes (NTMs). A high G-factor, (a major of fusion gain), of 0.54 and a large f BS > 0.43 are suitable for ITER hybrid operation scenario. Based on the plasma for ITER hybrid operation scenario, the high βN of 2.1 with good thermal plasma confinement of H H98(y,2) > 0.85 is sustained for longer than 12 s at and f rad > 0.79. Physics studies for the development of AT plasmas, physics studies of H-mode, pedestal and ELM characteristics and physics studies on impurity transport, SOL/divertor plasmas and plasma–wall interactions are also in progress. The active NTM stabilization system using modulated ECCD, which is synchronized to rotating island, has been developed and the efficiency of modulated ECCD in m/n = 2/1 NTM stabilization has been demonstrated. The intrinsic toroidal rotation driven by the ion pressure gradient and by the ECH is confirmed. The dedicated H-mode and pedestal experiments indicate two scalings, H-factor evaluated for the core plasma as and pedestal width scaling of . New fast diagnostics with high spatial and temporal resolutions reveals the different structures of pedestal pressure between co- and counter-rotating plasma, resulting in different ELM sizes determined by the radial penetration depth of the ELM crash. The tungsten accumulation becomes more significant with increasing toroidal rotation in the counter-direction.

Ballooning theory of the second kind—two dimensional tokamak modes

“…Substituting Eqs. (34) and (35) into Eq. (33) yields the contribution from the jth rational surface to < k…”

“…[32][33][34][35] The spontaneous symmetry breaking induced parallel Reynolds stress is a ubiquitous turbulence driven mechanism for sowing seeds for the intrinsic toroidal rotation. This feature, however, is not unique to ITG and is common to all types of tokamak turbulence because of the 2-D mode structure imposed by the tokamak geometry.…”

A Review of Fusion and Tokamak Research Towards Steady-State Operation: A JAEA Contribution

“…Since then, significant efforts to achieve reactors relevant high temperature plasma and provide a scientific basis for ITER and the SSTR have been made in JT-60 and JT-60U during 23 years of research operation exploring advanced regimes relevant to the steady state operation of tokamaks. The progress and findings in these areas are presented in a topical review of Nuclear Fusion [8], a special issue of Fusion Science and Technology [9], IAEA conferences [10][11][12][13][14][15][16][17][18][19][20][21], American Physical Society meetings [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], European Physical Society meetings [40][41][42][43][44][45][46][47][48][49][50][51][52][53]…”

“…Especially, the establishment of a physics basis for steady state operation has becomes one of main research elements of JT-60U [14][15][16][17][18][19][20][21][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][46][47][48][49][50][51][52][53][54][55].…”

“…On the drift time scale, −A/t term is negligible and we can write E = −. Taking the dot product of the magnetic field B with (13) and (14) and taking the flux surface average, following flux surface averaged momentum and heat flux balance equation are obtained:  B   a   (P //a  P a )b B (21)  B   a   ( //a  a )b B (22) In 1995, a comprehensive review on the experimental evidence for the bootstrap current was given [109]. In this paper, the origin of this velocity space anisotropy is pictorially explained in case of the electron as in Figure 19.…”