Investigation of multi-frequency generation in the FEM

The FOM Fusion FEM project involves the construction and operation of a 1-MW, 100 ms pulse, rapid tunable FEM in the 130–250 GHz range for fusion applications. The undulator of the FEM consists of two sections with different strengths and different lengths separated by a gap without undulator field. The design provides arbitrary focussing. Single frequency codes predict a much higher output power for the two-section undulator than for a one-section undulator. However, the different undulator strengths lead to different resonance conditions and therefore, in principle, multiple frequencies can be generated. This problem of multi-frequency generation due to the two-section undulator is under investigation. First results are presented in this paper. The longitudinal mode structure of the FEM is simulated in a multi-pass, multi-frequency code. In this code the electrons are described fully 3D, non-wiggler averaged and in the long pulse limit. AC longitudinal space-charge forces are included. The radiation field is considered to have the known transverse radial dependence of a HE11-mode, due to the rectangular corrugated waveguide of the FEM. A multi-pass calculation in the single-frequency limit is presented, where the field grows into saturation

Spectal dynamics of a collective free electron maser

A study of the nonlinear spectral dynamics of a Free Electron Maser (FEM) is reported. In the FEM for fusion applications [1], the electron beam is modulated by a step-tapered undulator consisting of two sections with different strengths and lengths. The sections have equal periodicities and are separated by a field-free gap. The microwave beam is guided in a rectangular corrugated waveguide. The electron energy is rather low and the current density is large, therefore, the FEM operates in the collective (Raman) regime. The dynamics of the spectrum is calculated with a code that is based on a multifrequency model in the continuous beam limit with a 3D description of the electron beam. Space-charge forces are included. They strongly influence the behaviour of the generated spectrum. In the saturated regime the gain is still relatively high because of the large outcoupled power fraction. It is discussed that quite robust parameter regions exist, where single-peaked frequency spectra are excited

Database of measurements on the offshore wind farm Egmond aan Zee

This paper presents the database of the measurements that have been acquired over the years in the Offshore Wind farm Egmond aan Zee (OWEZ). In addition, two topics are discussed: the analyses on this database that were performed in the past, and the potential for new analyses in the framework of the EU/FP7 project MaRINET. The OWEZ database and the analyses performed on it offer a unique opportunity to study the external conditions of an offshore wind energy site.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin