Numerical simulation of the effect of pellet injection on ELMs

Abstract

We report on numerical simulation studies of the dynamical behavior of edge localized modes (ELMs) under the influence of repetitive injection of pellets. In our nonlinear 2-fluid model the ELMs are excited by introducing a particle source in the confinement region and a particle sink in the edge region. The injection of pellets is simulated by periodically raising the edge density in a pulsed manner. We find that when the edge density is raised to twice the normal edge density with a duty cycle (on time:off time) of 1:2, the ELMs are generated on an average at a faster rate and with reduced amplitudes. These changes lead to significant improvements in the plasma beta indicative of an improvement in the energy confinement due to pellet injection. Concurrently, the plasma density and temperature profiles also get significantly modified. A comparative study is made of the nature of ELM dynamics for different magnitudes of edge density enhancements. We also discuss the relative impact on ELMs from resonant magnetic perturbations (RMPs) compared to pellet injection in terms of changes in the plasma temperature, density, location of the ELMs and the nonlinear spectral transfer of energies.

A nonlinear simulation study of the effect of toroidal rotation on RMP control of ELMs

“…The particle, energy and momentum sources are modelled with relatively simple model profiles. Thus, the equilibrium and the turbulence are co-evolved with essentially the same assumptions as used in our earlier works dealing with ELMs [19][20][21]. Likewise, the prescriptions for the RMP and flows are schematic and are not intended to be quantitatively accurate.…”

“…The model equations for our simulations, as used in CUTIE, have been described in details in the past [17][18][19]21]. For the sake of completeness and to make the paper self-contained we list them below.…”

“…CUTIE is capable of simulating multiple edge relaxation periods and has in the past also successfully modelled the L-H transition behaviour in COMPASS-D [19]. More recently CUTIE has been used to study ELM dynamics in the presence of RMPs [20] as well as pellet injection [21].…”

Bifurcation behaviour of resonant magnetic perturbation control of edge localized modes in tokamaks: nonlinear simulation results

“…Recent works [10][11][12][13][14][15][16] have tackled the challenge of explaining the mechanism of resonant magnetic perturbation (RMP) control (by mitigation/suppression) of type-I ELMs observed in several experiments [17][18][19][20][21]. The simulations presented in this article were carried out using the Culham Transporter of Ions and Electrons (CUTIE) [8,12,[22][23][24][25] -a two-fluid electromagnetic nonlinear global code. The full details related to ELM simulations without and with RMPs are available in [8,12].…”

“…[ 8 , 12 ] that ELMs are two-fluid versions of the PBMs of MHD that occur due to the pressure gradients created by a particle source in the plasma and a simulated scrape off layer (SOL) using a sink exterior to the plasma. CUTIE is capable of simulating multiple ELM relaxation periods in COMPASS-D [ 8 ], as well as ELM dynamics in the presence of RMPs [ 24 , 25 ]. In this article, we aim to address some important bifurcation phenomena observed in recent experiments with RMP control of ELMs in tokamaks.…”