Effects of Resonant Magnetic Perturbation on Particle Transport in LHD

In this study, the effects of resonant magnetic perturbation (RMP) on particle transport are investigated in Large Helical device (LHD). The magnetic configuration is selected to be the outwardly shifted configuration, for which the magnetic axis position (Rax) is 3.9 m. At Rax = 3.9 m, the main plasma is surrounded by a thick ergodic layer, with width of about 30% of the plasma minor radius. The perturbation mode m/n = 1/1, where m and n are poloidal and toroidal mode numbers, is applied. The resonant layer is around the last closed flux surface. With RMP, a region in which both the connection and Kolmogorov lengths are finite and the magnetic field is ergodic forms; this region extends inside the main plasma. In the low-collisionality regime, where νh* 1), a clear difference in particle transport is found. A clear difference in turbulence is also observed, suggesting that turbulence plays a significant role in particle transport in the high-collisionality regime both with and without RMP

Overview of transport and MHD stability study: focusing on the impact of magnetic field topology in the Large Helical Device

The progress in the understanding of the physics and the concurrent parameter extension in the large helical device since the last IAEA-FEC, in 2012 (Kaneko O et al 2013 Nucl. Fusion 53 095024), is reviewed. Plasma with high ion and electron temperatures (Ti(0) ~ Te(0) ~ 6 keV) with simultaneous ion and electron internal transport barriers is obtained by controlling recycling and heating deposition. A sign flip of the nondiffusive term of impurity/momentum transport (residual stress and convection flow) is observed, which is associated with the formation of a transport barrier. The impact of the topology of three-dimensional magnetic fields (stochastic magnetic fields and magnetic islands) on heat momentum, particle/impurity transport and magnetohydrodynamic stability is also discussed. In the steady state operation, a 48 min discharge with a line-averaged electron density of 1 × 1019 m−3 and with high electron and ion temperatures (Ti(0) ~ Te(0) ~ 2 keV), resulting in 3.36 GJ of input energy, is achieved

Extension of the operational regime of the LHD towards a deuterium experiment

As the finalization of a hydrogen experiment towards the deuterium phase, the exploration of the best performance of hydrogen plasma was intensively performed in the large helical device. High ion and electron temperatures, Ti and Te, of more than 6 keV were simultaneously achieved by superimposing high-power electron cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value $\left\langle \beta \right\rangle$ . The high $\left\langle \beta \right\rangle$ regime around 4% was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with a wide range of edge plasma parameters. The existence of a no impurity accumulation regime, where the high performance plasma is maintained with high power heating  >10 MW, was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region