Particle-in-cell (PIC) simulations of beam instabilities in gyrotrons

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During initial studies of ECRH in the TCV tokamak, non-standard central MHD activities, such as humpbacks and saturated and inverted sawteeth, have been observed while changing the heating location, the ECRH power, the plasma shape and the safety factor. For edge safety factors q(alpha) > 4.5, safety factors on-axis q(0) < 1 and small plasmas, complete sawtooth stabilization was achieved with the present 1 MW gyrotron power, and it is likely that sawtooth stabilization can be achieved for all conditions at.

A dynamical theory of multiphoton transitions in semiconductors is developed using a density matrix approach. It is shown that, in dipole approximation, these transitions require a mixed parity of the basis stales and that band-diagonal coupling's of the electromagnetic field to Bloch electrons have to be included. The general theory is outlined using the simple, but solvable model of a diatomic tight-binding chain. Possible extensions and applications of the approach are discussed.

Global Alfven eigenmodes are studied using fluid and kinetic plasma models to determine how the finite Larmor excursions of the bulk species and the resonant Landau interactions modify the spectrum in the toroidicity Alfven eigenmode (TAE) range of frequencies. A new kinetic Alfven mode conversion mechanism is described taking place away from the resonances through toroidal coupling, when the spatial scales of the fast and the kinetic Alfven waves become comparable. If the Landau damping of the mode convert

This thesis deals with the monolithic integration of long wavelength (1.3-1.55 µm) p-i-n photodiodes with HEMT field effect transistors for the realization of wide bandwidth OEIC receivers for lightwave communication systems. Part of this work was carried out in collaboration with the Laboratory for Electromagnetic Fields and Microwave Electronics (IFH) of the ETH-Zürich. The p-i-n photodiode structure consisting of a n+-InP lower contact layer, a 1 µm undoped InGaAs absorption layer and a 100 nm p+-InGaAs

Particle-in-cell (PIC) simulations of beam instabilities in gyrotrons

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Behaviour of central plasma relaxation oscillations during localized electron cyclotron heating on the TCV tokamak

Dynamical density matrix theory of multiphoton transitions in semiconductors

Kinetic Alfvén eigenmodes in a hot tokamak plasma

Photorécepteurs 1,3-1,55 µm obtenus par intégration monolithique de photodiodes p-i-n et de transistors HEMT