ISBN 9783843910613

978-3-8439-1061-3, Reihe Ingenieurwissenschaften

Andreas Stock
A High-Order Particle-in-Cell Method for Low Density Plasma Flow and the Simulation of Gyrotron Resonator Devices

179 Seiten, Dissertation Universität Stuttgart (2013), Softcover, A5

Zusammenfassung / Abstract

Within this thesis a parallelized, transient, three-dimensional, high-order discontinuous Galerkin Particle-in-Cell solver is developed and used to simulate the resonant cavity of a gyrotron.

The discontinuous Galerkin approach - a Finite-Element type method - provides a fast and efficient algorithm to numerically solve Maxwell's equations. Besides its excellent parallelization capabilities, the discontinuous Galerkin approach easily allows for using unstructured grids, as required to simulate complex-shaped engineering devices. These properties are essential for the efficient numerical treatment of the Vlasov-Maxwell system with the Particle-in-Cell method. This system describes the self-consistent interaction of charged particles and the electromagnetic field.

The gyrotron is a high-power millimeter wave source, used for the electron cyclotron resonance heating of magnetically confined fusion plasma. Compared to state-of-the-art simulation tools used for the design of gyrotron resonators the Particle-in-Cell method does not use any significant physically simplifications. Hence, it is the method of choice for validation of current simulation tools being restricted by these simplifications. Using the presented high-order discontinuous Galerkin Particle-in-Cell scheme on high-performance-computers, this thesis demonstrates for the first time that full-wave and transient research- and design-simulations of gyrotron resonators with high mode-indices can be efficiently performed. The scheme is used to simulate the resonator of the 1 MW, 140 GHz gyrotron, used for plasma heating of the Wendelstein 7-X fusion-reactor.

The presented simulations provide new physical insights to the complex particle-field-interaction appearing in gyrotrons. They can be used to analyse transient phenomena, such as beam-miss-alignment, mode competition or interaction appearing at the end of the resonator, so called after-cavity-interactions. Furthermore, this work demonstrates the ability of the discontinuous Galerkin Particle-in-Cell code to simulate the coupled resonator and quasi-optical antenna (launcher) of a gyrotron. These high-order simulations enable a holistic analysis of the interaction in a gyrotron. Furthermore, they pave the road to a complete simulation of a gyrotron, considering all its components, with a high-order discontinuous Galerkin Particle-in-Cell scheme - as presented here - on future high-performance-computers.