Improved plasma performance on Large Helical Device

Since the start of the Large Helical Device (LHD) experiment, various attempts have been made to achieve improved plasma performance in LHD [A. Iiyoshi et al., Nucl. Fusion 39, 1245 (1999)]. Recently, an inward-shifted configuration with a magnetic axis position R_ax of 3.6 m has been found to exhibit much better plasma performance than the standard configuration with R_ax of 3.75 m. A factor of 1.6 enhancement of energy confinement time was achieved over the International Stellarator Scaling 95. This configuration has been predicted to have unfavorable magnetohydrodynamic (MHD) properties, based on linear theory, even though it has significantly better particle-orbit properties, and hence lower neoclassical transport loss. However, no serious confinement degradation due to the MHD activities was observed, resolving favorably the potential conflict between stability and confinement at least up to the realized volume-averaged beta of 2.4%. An improved radial profile of electron temperature was also achieved in the configuration with magnetic islands, minimized by an external perturbation coil system for the Local Island Divertor (LID). The LID has been proposed for remarkable improvement of plasma confinement like the high (H) mode in tokamaks, and the LID function was suggested in limiter experiments

Transition From Ion Root to Electron Root in NBI Heated Plasmas in LHD

Recent Large Helical Device (LHD) experiments revealed that the transition from ion root to electron root occurred for the first in neutral beam heated discharges, where there is no non-thermal electrons exist. The measured values of the radial electric field were found to be in qualitative agreement with those estimated by neoclassical theory. For the configuration with a magnetic axis of 3.75m, where the ion transport loss was comparable to the neoclassical ion loss, a clear reduction of ion therrnal diffusivity was observed after the mode transition from ion root to electron root as predicted by neoclassical theory. On the other hand, for the inward shifted configuration (Rax=3.6m), where the neoclassical ion loss is reduced below the anomalous loss, no change in the ion thermal diffusivity was observed

MHD Characteristics in High-beta Regime of the Large Helical Device

The highest volume averaged beta value beta_t of 2.2% at B_t = 0.75 T (gas puff) and 2.4 % at B_t = 1.3 T (pellet) in all of helical devices have been achieved in the Large Helical Device (LHD). The beta_t dependence of MHD activities has been investigated in NBI plasmas. The n/m = l/2 mode excited in the core region and / = l resonant modes in peripheral region have been observed. Both of the fluctuation amplitudes increase with beta_t and the pressure gradient. The strong n/m = l/2 mode which affects plasma profile have been observed in high-beta_t discharges and the abrupt disappearance of the mode leads to the restoration of T_e profile. Violent instabilities which terminate the plasma and degradation of global energy confmement have not been observed so far

Study of Energetic Ion Transport in the Large Helical Device

"The confinement property of high energy ions and the role of ripple induced transport have been studied in the Large Helical Device (LHD). Tangential beam particles are injected at 90 - 150 kV by negative-ion-based neutral beam injectors, and perpendicular high energy particles are generated by lon Cyclotron Range of Frequency (ICRF) heating. Energy distributions of high energy ions have been measured by fast neutral particle analyzers based on natural diamond detectors, specially developed for this experiment. Time evolution of perpendicular tail temperature in decaying phase after the ICRF termination indicates that the fast particles deeply trapped in helical repples are well confined longer than the collisional relazation time, when n_e > 10^19 m^-3 in the inward shifted configuration (R_ax = 3.6 m). In lower density plasma, however, faster decay than the classical prediction is observed. The tangential energy spectra in a low density steady state plasma of the standard configuration (R_ax=3.75m) also show the deviation from 2D Fokker-Pland simulation. The global 5-D transport simulation code including the ripple induced transport in shows good agreement with measured spectra, and this suggests an important role of ripple induced transport in the standard configuration of LHD.

Energy Confinement and Thermal Transport Characteristics of Net-Current Free Plasmas in Large Helical Device

The energy confinement and thermal transport characteristics of net-current free plasmas in the much smaller gyro-radii and collisionality regimes than before have been investigated in the Large Helical Device (LHD). The inward shifted configuration that is superior from the theoretical aspect of neoclassical transport has revealed a systematic confinement improvement on a standard configuration. The improvement of energy confinement times on the international stellarator scaling 95 occurs with a factor of 1.6 pm 0.2 for an inward shifted configuration. This enhancement is primarily due to the broad temperature profile with a high edge value. A simple dimensional analysis involving LHD and other medium sized heliotrons yields strongly gyro-Bohm dependence (tau_E Omega propto rho^ast-3.8) of energy confinement times. It should be noted that this result is attributed to comprehensive treatment of LHD for systematic confinement enhancement and that the medium sized heliotrons have narrow temperature profiles. The core stored energy still indicates the dependence of tau_E omega propto rho^ast-2.6 when data only from LHD is processed. The local heat transport analysis of dimensionally similar discharges except for rho^ast suggests that the heat conduction coefficient lies between Bohm and gyro-Bohm in the core and changes towards strong gyro-Bohm in the peripheral region. Since the inward shifted configuration has a geometrical feature suppressing the neoclassical transport, confinement improvement can be maintained in the collisionless regime where the ripple transport is important. The stiffness of the pressure profile coincides with enhanced transport in the peaked density profile obtained by pellet injection

Characterization of the Interaction of Hypericin with Protein Kinase C in U-87 MG Human Glioma Cells

A fluorescence imaging technique was used to monitor intracellular localization of protein kinase C (PKC) in U-87 MG human glioma cells in the presence of hypericin (Hyp) and phorbol 12-myristate-13-acetate (PMA). It is shown that PKC localization, which reflects its activity, is influenced by Hyp and this influence is different from that observed for PMA which acts as PKC activator. Fluorescence binding experiments were used to determine the binding constants of Hyp to several isoforms of PKC. The obtained values of K(d)s (approximately 100 nM) suggest that Hyp binds with high affinity to PKC. Finally, molecular modeling was used to compare structural models of the interaction of C1B domain of PKC (PKC isoforms alpha, delta, gamma) with Hyp and our previously published model of the (C1B domain PKCgamma)/PMA complex. The influence of Hyp on PKC translocation in U-87 MG cells in comparison with PMA, colocalization fluorescence pattern of Hyp and PKC, the higher binding affinity of Hyp to PKC in comparison with known binding constants of phorbol esters, as well as the binding mode of Hyp and PMA to the C1B domain of PKC suggested by molecular modeling, support the idea that Hyp and PMA might competitively bind to the regulatory domain of PKC