Global modelling of tungsten impurity transport based on the drift-kinetic equation, Nuclear Fusion

A global kinetic simulation model of collisional impurity transport is developed for evaluating the radial particle flux of tungsten impurity in the edge region of a tokamak plasma. Here, the plasma including the impurity and the background ion is presupposed to be quasi-steady. The simulation model is based on the drift-kinetic equation of the impurity affected by the friction force and the thermal force, which were formulated in the previous study (Homma et al 2016 Nucl. Fusion 56 036009). The model is implemented in a drift-kinetic simulation code. We find that the magnetic drift term in the drift-kinetic equation causes the \u27global effect\u27 on the impurity transport. Here, the global effect means that the solution of the drift-kinetic equation (and also the radial particle flux) on a magnetic flux surface is influenced by the values of the solution all over the edge region

The development of a zero-dimensional collisional-radiative model for interpreting plasma emission in low temperature divertor plasmas in tokamaks

Collisional-radiative models are commonly used to analyse atomic and molecular processes in low temperature plasmas by determining the distribution functions of excited states as functions of various plasma parameters. This paper outlines the improvements to a zero-dimensional collisional-radiative model, developed at Keio University, for purposes relevant to the analysis of emission measurements in low temperature hydrogen plasmas. The extension of this 0D model centres on the inclusion of additional molecular species and reactions, a calculation of emission intensity in order to directly compare with experimental work, and the addition of a simple wall model to allow for a deeper understanding of recycling of atoms and molecules in low temperature plasmas close to plasma facing components in fusion machines. Results from the improved model are then compared with both an existing CR model for benchmarking and experimental emission spectroscopy data from an inductively-coupled plasma device at the University of Liverpool. These results show how the developments to the model have increased the relevance to experimental plasmas, such as those in the power exhaust regions of fusion machines, with the ratio of the Hβ/Hα line intensities outputted from the improved CR model mirroring more closely the emission measured experimentally in the ICP device

Effects of the Plasma Blob Nonlinear Formation/Transport on Impurity Transport in the SOL Regions

The purpose of this study is to make clear the effects of the plasma blob on the impurity transport in the Scrape-Off Layer (SOL) regions. By using the two-dimensional (2D) interchange turbulence model with plasma transport along magnetic field line, we have simulated the plasma blob formation and transport in the SOL regions. We have studied the effects of the plasma blob on the impurity transport by using impurity equations of motion in the trace impurity limit. The results show that the plasma blob transport direction is not only the radial direction but also poloidal direction due to the plasma transport along the magnetic field line. Also, the impurity ions are transported radially outward with the plasma blob transport and the velocity of the impurity ions transport is the same order to the plasma blob velocity radially outward. These results implied that the impurity transport with the plasma blob may possibly be not only diffusion but also convection. Moreover, this motion of the impurity ions seems like eddy motion. As a next step, we study relation between this eddy motion of impurity ions and the plasma blob motion. That is our future work

IMPGYRO: The Full-Orbit Impurity Transport Code for SOL/Divertor and its successful application to tungsten impurities

In future fusion reactors, tungsten (W) is currently regarded as one of the most feasible candidates for the plasma-facing components (PFCs). Once the W impurities sputtered from the PFCs penetrate into the core plasma, the large radiation cooling and fuel dilution, which leads to the deterioration of the core plasma performance, take place. To understand and to control W impurity transport are indispensable for future fusion reactors. In order to understand W transport, we are continuing to develop the kinetic impurity transport code IMPGYRO for SOL/divertor in fusion reactors. The IMPGYRO has obtained following unique features compared to other existing kinetic impurity transport codes through the 15-years development activity; (i) the exact Larmor motion of impurity ions are computed so that the effects of drifts are automatically taken into account, (ii) the Coulomb collision between impurities and background plasma ions are modelled by the Binary Collision Method which kinetically calculates more precise friction and thermal forces, and (iii) the background plasma transport and impurity transport are computed self-consistently by the coupled calculation with SOL/divertor plasma transport code such as SOLPS-ITER. Although the IMPGYRO transport model has significantly improved from the initial development phase, the modelling improvement of the IMPGYRO has never been described in detail. In this paper, (a) the current W generation/transport model, and (b) the coupling strategy between the SOLPS-ITER and the IMPGYRO are summarized. The new results (c) the check of the prompt re-deposition model of the IMPGYRO, and (d) the further extension of the Coulomb collision modelling of the IMPGYRO towards the neoclassical (NC) transport handling capability has been performed. The effects of the NC transport processes on a simple circular tokamak geometry are compared with the anomalous diffusion by means of the extended IMPGYRO to obtain better understanding of cross-field transport process of W. The results show that the NC transport process may become non-negligible compared to the anomalous diffusion at least in this configuration. Based on these recent improvements, the present version of the IMPGYRO is very useful tool for understanding and prediction of W transport in SOL/divertor regions of fusion devices

Effects of Gyro Motion of High-Z Impurity on Transport in the Scrape-Off Layer

従来のSOL領域での不純物輸送解析には不純物のラーマー旋回半径が十分に小さいとして、旋回中心近似が広く用いられていた。近年ダイバータ板材料としてタングステン(W)を用いることが有力視されており、その質量の大きさにより、有限ラーマー旋回効果が無視できないことが指摘されている。本研究ではW不純物を対象とし、不純物の旋回運動まで追跡する完全軌道コードと旋回中心近似コード間の結果の比較を行った。その結果、SOL領域上流にW不純物が対流した場合、ラーマ旋回効果に起因する磁気ドリフトおよび温度遮蔽効果が炉心へのW不純物侵入量に無視できない影響を与えることがわかった。17th International Workshop on Plasma Edge Theory in Fusion Devices (PET17