arXiv subjects

P. C. de Vries

Publications and source records attributed to P. C. de Vries.

5 recordsLinked to original sources

arXiv2026

Self-consistent modelling and qualitative comparison of mildly relativistic runaway electron dynamics with a closed flux surface formation model during tokamak startup

A model for mildly relativistic Runaway Electrons (REs) is developed in a reduced-kinetic form and qualitatively compared with radiation characteristics observed in KSTAR ohmic startup. The mildly relativistic correction not only alleviates runaway current overestimation but also accounts for the partial parallel confinement of the initial runaway seed under an open-field configuration during early burn-through. The model is self-consistently integrated in the state-of-the-art predictive plasma initiation code DYON (Hyun-Tae Kim et al 2022 Nucl. Fusion 62 126012), hereafter referred to as DYON-RE. DYON-RE provides an improved RE confinement model during the transition from an open to a closed magnetic configuration by employing a model-based description of closed flux surface formation validated in multi machines. We show prediction capability of DYON-RE in two representative discharges among KSTAR ohmic startups. DYON-RE reliably predicts key plasma parameters such as plasma current, density, and temperature and also implies the characteristic behavior of the radiative temperature measured by electron cyclotron emission diagnostics in agreement with experimental results. The proposed model offers a framework for designing runaway-free ohmic startup scenarios in CPD and ITER. Future experimental validation will further refine its predictive capabilities and broaden its practical application.

physics.plasm-ph↗

arXiv2025

The role of nonlinear absorption of an ECR beam for fusion plasma pre-ionization

This study investigates the nonlinear interactions between electrons and electron-cyclotron resonance (ECR) heating beams in magnetized, low-temperature fusion plasmas, focusing on enhancing pre-ionization efficiency. We analyse key parameters affecting ECR absorption, including phase angle, temperature inhomogeneity, magnetic field gradients, and beam characteristics like width and frequency. Using 2D simulations for these low temperature plasmas, we demonstrate electrons gain energy through nonlinear trapping in velocity space near the resonance layer, achieving energy levels up to 1 keV under optimal conditions. Notably, narrow beam widths allow electrons to reach higher energy levels more efficiently than broader beams, highlighting the spatial localization of the nonlinear interactions to regions where the field is strong and frequency mismatch is small. Our findings show that in devices with lower-frequency ECR systems, such as TCV (82.7 GHz), electrons can gain up to 800 eV, while higher-frequency devices, like ASDEX-Upgrade (140 GHz) and ITER (170 GHz), achieve lower energy gains (480 eV and 420 eV, respectively) under similar conditions. These insights are directly applicable to improving ECR heating strategies, informing design choices in future fusion devices to optimize energy transfer during plasma breakdown and startup.

physics.plasm-ph↗

arXiv2024

Inelastic collisions facilitating runaway electron generation in weakly-ionized plasmas

Dreicer generation is one of the main mechanisms of runaway electrons generation, in particular during tokamak startup. In fully ionized plasma it is described as a diffusive flow from the Maxwellian core into high energies under the effect of the electric field. In this work we demonstrate a critical role of the non-differential nature of inelastic collisions in weakly ionized plasma during tokamak startup, where some electrons experience virtually no collisions during acceleration to the critical energy. We show that using the Fokker-Planck collisional operator can underestimate the Dreicer generation rate by several orders of magnitude.

physics.plasm-ph↗

arXiv2014

Plasma burn-through simulations using the DYON code and predictions for ITER

This paper will discuss simulations of the full ionization process (i.e. plasma burn-through), fundamental to creating high temperature plasma. By means of an applied electric field, the gas is partially ionized by the electron avalanche process. In order for the electron temperature to increase, the remaining neutrals need to be fully ionized in the plasma burn-through phase, as radiation is the main contribution to the electron power loss. The radiated power loss can be significantly affected by impurities resulting from interaction with the plasma facing components. The DYON code is a plasma burn-through simulator developed at Joint European Torus (JET) [1] [2]. The dynamic evolution of the plasma temperature and plasma densities including impurity content is calculated in a self-consistent way, using plasma wall interaction models. The recent installation of a beryllium wall at JET enabled validation of the plasma burn-through model in the presence of new, metallic plasma facing components. The simulation results of the plasma burn-through phase show consistent good agreement against experiments at JET, and explain differences observed during plasma initiation with the old carbon plasma facing components. In the International Thermonuclear Experimental Reactor (ITER), the allowable toroidal electric field is restricted to 0.35 [V/m], which is significantly lower compared to the typical value (~ 1 [V/m]) used in the present devices. The limitation on toroidal electric field also reduces the range of other operation parameters during plasma formation in ITER. Thus, predictive simulations of plasma burn-through in ITER using validated model is of crucial importance. This paper provides an overview of the DYON code and the validation, together with new predictive simulations for ITER using the DYON code.

physics.plasm-ph↗

arXiv2013

The effect of ITER-like wall on runaway electron generation in JET

This paper investigates the effect of the ITER-like wall (ILW) on runaway electron (RE) generation through a comparative study of similar slow argon injection JET disruptions, performed with different wall materials. In the carbon wall case, a runaway electron plateau is observed, while in the ITER-like wall case, the current quench is slower and the runaway current is negligibly small. The aim of the paper is to shed light on the reason for these differences by detailed numerical modelling to study which factors affected the RE formation. The post-disruption current profile is calculated by a one-dimensional model of electric field, temperature and runaway current taking into account the impurity injection. Scans of various impurity contents are performed and agreement with the experimental scenarios is obtained for reasonable argon- and wall impurity contents. Our modelling shows that the reason for the changed RE dynamics is a complex, combined effect of the differences in plasma parameter profiles, the radiation characteristics of beryllium and carbon, and the difference of the injected argon amount. These together lead to a significantly higher Dreicer generation rate in the carbon wall case, which is less prone to be suppressed by RE loss mechanisms. The results indicate that the differences are greatly reduced above ~50% argon content, suggesting that significant RE current is expected in future massive gas injection experiments on both JET and ITER.

physics.plasm-ph↗