Particle transport of electron cyclotron resonant heating plasma in Large Helical Device

Abstract

The particle diffusion coefficient and convection velocity of electron cyclotron resonant heating plasmas have been evaluated using a density modulation experiment in the Large Helical Device. The diffusion coefficients and convection velocities were estimated by a newly developed analysis method. This method combines conventional quasi-Newton optimization and a genetic algorithm (GA). The GA finds the appropriate initial values. By giving the appropriate initial values for the quasi-Newton method, falling into an inappropriate solution which is not applicable for transport physics such as negative diffusion coefficients or extremely high values can be avoided. The diffusion coefficient obtained with the modulation experiment (D mod ) in the core region increases monotonically with the increase of the effective collisionality (n h *). The experimental results of D mod and the convection velocity (V mod ) can reconstruct the density profile at n < 1.5 h * , but they do not reconstruct it at n > 1.5 h * . The values of D mod were from several times to three orders higher than those obtained by neoclassical prediction. On the other hand, V mod was comparable with the neoclassical estimation. Ion-scale microturbulence was measured and compared with D mod and V mod . The comparison suggested possible linkage between the two.

Development of Two-Color Laser Imaging Interferometer Using CO₂Laser and Quantum Cascade Laser in the Large Helical Device

“…In this section, an example of the evaluated radial density profiles in gas-fueled plasma is presented. To evaluate the radial density profiles, we used the Abel inversion with an optimized regularization parameter using GCV [2,25,26]. Compared with FIR laser interferometers, which apply the same optimized Abel inversion [2], the CO 2 /QC laser interferometer has a fine spatial resolution and does not require interpolation between channels [12].…”

“…To evaluate the radial density profiles, we used the Abel inversion with an optimized regularization parameter using GCV [2,25,26]. Compared with FIR laser interferometers, which apply the same optimized Abel inversion [2], the CO 2 /QC laser interferometer has a fine spatial resolution and does not require interpolation between channels [12]. In this schema, the flux surface is determined by the interpolation of a pre-calculated equilibrium database [27].…”

“…In addition, the interferometer provides essential information for physical investigations. For instance, flux surface-averaged radial density profiles evaluated by the Abel inversion of multichannel line-integrated density were used for transport analyses and stability calculations [1,2]. In addition, the fine temporal evolution of electron density can be used to investigate macro-and micro-instabilities [3,4].…”

Effects of core stochastization on particle and momentum transport

“…It should be noted that MHD modes are not observed in the core. The n e profiles shown in figure 2(b) are reconstructed from the line-integrated density n e L obtained with a 13 ch FIR laser interferometer [18,19] by using Tikhonov Phillips regularization and generalized cross-validation [20,21]. The density profile of the ctr-ECCD plasma is hollower than those of the bal-ECCD and the co-ECCD plasmas, indicating that the particle transport of these plasmas is different.…”

“…Here, the diffusion coefficient and the convection velocity evaluated from the modulation experiment are denoted as D mod and V mod . The detailed analysis method for the estimation of D mod and V mod is shown in reference [20].…”