Dynamics of three-dimensional radiative structures during RMP assisted detached plasmas on the large helical device and its comparison with EMC3-EIRENE modeling

Abstract

The resonant magnetic perturbation (RMP) island introduced in the stochastic edge of the large helical device (LHD) plasma plays an important role in the stabilization of the plasma detachment (Kobayashi et al 2013 Nucl. Fusion 53 093032). The plasma enters in the sustained detachment phase in the presence of an RMP once the line averaged density exceeds a critical value with a given input power. During detachment the enhanced radiation from the stochastic edge of the LHD undergoes several spatiotemporal changes which are studied quantitatively by an infrared imaging video bolometer (IRVB) diagnostic. The experimental results are compared qualitatively and quantitatively with the radiation predicted by the 3D transport simulation with fluid model, EMC3-EIRENE. A fair amount of qualitative agreement, before and after the detachment, is reported. The issue of overestimated radiation from the model is addressed by changing the free parameters in the EMC3-EIRENE code till the total radiation and the radiation profiles match closely, within a factor of two with the experimental observations. A better quantitative match between the model and the experiment is achieved at higher cross-field impurity diffusion coefficient and lower sputtering coefficient after the detachment. In this article a comparison, the first of its kind, is established between the quantified radiation from the experiments and the synthetic image obtained from the simulation code. This exercise is aimed towards validating the model assumptions against the experimentally measured radiation.

Monte-Carlo fluid approaches to detached plasmas in non-axisymmetric divertor configurations

“…[68]. The simulation results indicate selective cooling at the X-or Opoints of the magnetic island [64,68]. These results show the important role of the magnetic field structure on the evolution of divertor particle flux and radiated power distribution at the detachment transition.…”

“…The latter is attributed to the change of edge radiation distribution with respect to the m/n=1/1 magnetic island, that is, the movement of the radiation peak from the X-point to the O-point, as shown below in the comparison with experiments and also discussed in ref. [68]. The simulation results indicate selective cooling at the X-or Opoints of the magnetic island [64,68].…”

“…Details of the correspondence with the magnetic field structure are described in ref. [68]. In the attached phase, the radiation peaks in the upper right corner, where the X-point of the m/n=1/1 island is located, and the radiation extends along the divertor leg X-point, as shown in Fig.11 (g).…”

“…The IRVB views the plasma from the top of the torus and detects the radiation in the wavelength range of 0.15 ~ 1240 nm. The measured power is integrated over the field of view and plotted as a function of density in figure 10, together with the results from the corresponding synthetic diagnostic of EMC3-EIRENE [68]. In the simulation, the database in the STRAHL module is used to calculate the total carbon radiation.…”

“…Density increases from the top to bottom rows, and the detachment transition occurs after the first row. Adopted from ref [68]…”