7 research outputs found
Simulations of Kinetic Electrostatic Electron Nonlinear (KEEN) Waves with Variable Velocity Resolution Grids and High-Order Time-Splitting
KEEN waves are nonlinear, non-stationary, self-organized asymptotic states in
Vlasov plasmas outside the scope or purview of linear theory constructs such as
electron plasma waves or ion acoustic waves. Nonlinear stationary mode theories
such as those leading to BGK modes also do not apply. The range in velocity
that is strongly perturbed by KEEN waves depends on the amplitude and duration
of the ponderomotive force used to drive them. Smaller amplitude drives create
highly localized structures attempting to coalesce into KEEN waves. These cases
have much more chaotic and intricate time histories than strongly driven ones.
The narrow range in which one must maintain adequate velocity resolution in the
weakly driven cases challenges xed grid numerical schemes. What is missing
there is the capability of resolving locally in velocity while maintaining a
coarse grid outside the highly perturbed region of phase space. We here report
on a new Semi-Lagrangian Vlasov-Poisson solver based on conservative
non-uniform cubic splines in velocity that tackles this problem head on. An
additional feature of our approach is the use of a new high-order
time-splitting scheme which allows much longer simulations per computational e
ort. This is needed for low amplitude runs which take a long time to set up
KEEN waves, if they are able to do so at all. The new code's performance is
compared to uniform grid simulations and the advantages quanti ed. The birth
pains associated with KEEN waves which are weakly driven is captured in these
simulations. These techniques allow the e cient simulation of KEEN waves in
multiple dimensions which will be tackled next as well as generalizations to
Vlasov-Maxwell codes which are essential to understanding the impact of KEEN
waves in practice
A semi-Lagrangian code for nonlinear global simulations of electrostatic drift-kinetic ITG modes
A semi-Lagrangian code for the solution of the electrostatic drift-kinetic equations in straight cylinder configuration is presented. The code, CYGNE, is part of a project with the long term aim of studying microturbulence in fusion devices. The code has been constructed in such a way as to preserve a good control of the constants of motion, possessed by the drift-kinetic equations, until the nonlinear saturation of the ion-temperature-gadient modes occurs. Studies of convergence with phase space resolution and time-step are presented and discussed. The code is benchmarked against electrostatic Particle-in-Cell codes. (C) 2004 Elsevier B.V. All rights reserved
A semi-Lagrangian code for nonlinear global simulations of electrostatic drift-kinetic ITG modes
A semi-Lagrangian code for the solution of the electrostatic drift-kinetic equations in straight cylinder configuration is presented. The code, CYGNE, is part of a project with the long term aim of studying microturbulence in fusion devices. The code has been constructed in such a way as to preserve a good control of the constants of motion, possessed by the drift-kinetic equations, until the nonlinear saturation of the ion-temperature-gradient modes occurs. Studies of convergence with phase space resolution and time-step are presented and discussed. The code is benchmarked against electrostatic Particle-in-Cell codes
A drift-kinetic Semi-Lagrangian 4D code for ion turbulence simulation
A new code is presented here, named Gyrokinetic SEmi-LAgragian (GYSELA) code, which solves 4D drift-kinetic equations for ion temperature gradient driven turbulence in a cylinder (r, theta, z). The code validation is performed with the slab ITG mode that only depends on the parallel velocity. This code uses a semi-Lagrangian numerical scheme, which exhibits good properties of energy conservation in non-linear regime as well as an accurate description of fine spatial scales. The code has been validated in the linear and non-linear regimes. The GYSELA code is found to be stable over long simulation times (more than 20 times the linear growth rate of the most unstable mode), including for cases with a high resolution mesh (delta r similar to 0.1 Larmor radius, delta z similar to 10 Larmor radius). (c) 2006 Elsevier Inc. All rights reserved