Understanding plasma-wall interactions produced by the huge particle and heat fluxes reaching the vessel walls in nuclear fusion devices is of uttermost importance for the next generation of reactors. For example, the divertor of ITER is expected to withstand heat loads of around 10MW m-2 in steady state operation. To recreate these conditions, the linear plasma device Magnum-PSI is currently...
Experimental results in the first campaigns of Wendelstein 7-X (W7-X) have shown that, due to the optimization of the magnetic configuration with respect to neoclassical transport, turbulence is essential to understand and predict the total particle and energy fluxes. This has motivated much work on gyrokinetic modelling in order to interpret the already available experimental results and to...
The excitation of toroidicity induced Alfven eigenmodes (TAEs) using an electromagnetic antenna acting on a confined toroidal plasma is studied. The antenna is described by an electrostatic potential resembling the target TAE mode structure along with its corresponding parallel electromagnetic potential computed from Ohm's law. Stable long-time linear simulations are achieved by integrating...
Axisymmetric modes (i.e. with toroidal mode number n=0) destabilized by fast ions have been observed in recent JET experiments. Motivated by these experimental results, we have reconsidered the dispersion relation of macroscopic n=0 vertical displacements in shaped tokamak plasmas. Vertical displacements are normally stable thanks to a combination of passive and active feedback stabilization....
While the achievement of high confinement regime is ensured through the formation and sustainment of edge transport barriers associated with sheared flows, the effect of non-axisymmetric perturbations of the magnetic field, like non-resonant magnetic perturbations or ripple, on the transition remains an open issue. The underlying loss of axisymmetry is responsible for a toroidal torque,...
An improvement of the boundary conditions scheme of the 3D nonlinear MHD numerical code SpeCyl is presented. Boundary conditions have been shown to play a key role in the helical self-organization both in Reversed Field Pinch and tokamak plasmas. Two different sets of boundary conditions have been extensively tested against ubiquitous relaxation phenomena induced by plasma current in toroidal...
In this work, an implicit scheme for electromagnetic particle-in-cell/Fourier simulations is developed using the v_∥ formula and applied to studies of Alfvén waves in one dimension and in tokamak plasmas on structured meshes. While the “particle enslavement” scheme has been introduced for reducing the degree of freedom of particles in the field-particle system, in this work, we focus on the...
Filaments in the boundary of magnetically confined fusion plasmas lead to enhanced erosion of the main chamber walls. These high-density, coherent structures can be thought of as intermittent fluctuations described by the Filtered Poisson Process (FPP) as a superposition of pulses with a fixed shape and a constant duration. Additionally, these fluctuations have large amplitudes compared to the...
In a tokamak, radio frequency (RF) electromagnetic waves that propagate through low density plasma (n_l) enter the strongly turbulent edge region (n_e) before passing into the fusion plasma (n_p). Whether used for diagnostics or for heating and current drive, it is important to quantify the spectral properties of these waves. The magnetized n_l, n_p and n_e (via homogenization) regions are...
Three-dimensional force-free states describing toroidal plasmas with D-shaped cross section, are constructed. The construction is carried out by perturbing two-dimensional axisymmetric single-Beltrami states with translationally symmetric ones. The perturbation and the unperturbed magnetic field have a common Beltrami parameter λ, thus their superposition still satisfies the Beltrami equation....
H-mode plasma scenarios, with enhanced energy and particle confinement at plasma edge, are a viable option for fusion energy production and represent the core operational regimes for present day and next generation fusion experiments such as ITER. Good confinement however comes at the price of potentially large pressure and current density gradients in the edge region, leading to the so-called...
It has been experimentally observed in both tokamaks and stellarators that peaked density profiles lead to enhanced confinement regimes. The reduction in transport is believed to be related to the stabilization of ion-scale turbulence. In this conference contribution, we perform gyrokinetic simulations with the gyrokinetic code stella focusing on the effect of the density gradient on nonlinear...
Verification and validation of the internal kink instability in tokamak have been performed for both gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1-K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from the same equilibrium reconstruction of the DIII-D shot #141216, these codes exhibit excellent agreements for the growth rate and mode structure of the n=1...
