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Investigations of After Cavity Interaction in Gyrotrons Including the Effect of Non-uniform Magnetic Field
Dynamic after-cavity interaction (ACI) in megawatt-class gyrotrons is investigated that could lead to lower output mode purity and increased level of internal stray radiation. The self-consistent KIT-IHM multi-mode-code SELFT has been modified to extend the simulation domain into the radius up-taper section of the gyrotron cavity where the probability of ACI exists. Studies on four different gyrotron configurations confirm that undesired interactions in the up-taper region can result in additional parasitic oscillations with relative power in the 1%-range.
Modern Antenna Systems
The field of antenna engineering has been advancing at a remarkable pace to support modern communication systems. Recently, significant progress has been made in the development of new antennas and techniques targeted for applications in medical, defense, health care, communication, etc. The motivation of this project is to present cutting-edge research materials in the field of antennas for modern wireless communication.
Design and Experimental Investigation of a Second Harmonic 20 kW Class 28 GHz Gyrotron for Evaluation of New Emitter Technologies
Gyrotrons are high-power mm-wave tubes. Here, the design, construction and experimental investigation of a 20 kW, 28 GHz gyrotron (2nd harmonic) are reported. This tube was designed to evaluate new emitters for future highly efficient and reliable fusion gyrotrons and for material processing applications. Following experimental results have been achieved in CW operation: 22.5 kW output power at 23.4 kV electron beam voltage and 2.23 A beam current with the world record efficiency of 43 %.
Automated Mode Recovery and Electronic Stability Control for Wendelstein 7-X Gyrotrons
Magnetic confinement fusion relies on plasma heating and plasma control using gyrotron oscillators providing at megawatt power levels. The operational reliability decreases when operating at the performance limits due to increasing parasitic mode activity. This work demonstrates for the first time the automated, fast recovery of nominal gyrotron operation during a pulse by exploiting the hysteretic gyrotron behaviour after a mode switch being in use at the Wendelstein 7-X ECRH facility.
Temperature- and Time-Dependent Dielectric Measurements and Modelling on Curing of Polymer Composites
In this book a test set for dielectric measurements at 2.45 GHz during curing of polymer composites is developed. Fast reconstruction is solved using a neural network algorithm. Modeling of the curing process at 2.45 GHz using both dielectric constant and dielectric loss factor results in more accurate model compared to low frequency modelling that only uses the loss factor. Effect of various hardeners and different amount of filler is investigated.
Systematic Study of Key Components for a Coaxial-Cavity Gyrotron for DEMO
The physical design of cavity and magnetron injection gun (MIG) for a realistic, DEMO-compatible, coaxial-cavity 238 GHz 2 MW CW fusion gyrotron is developed in this work, having auxiliary frequencies at 170 GHz and 204 GHz. Novel systematic approaches towards multi-frequency mode selection, magnet requirements, and MIG design are presented. Mode deterioration and voltage depression variation due to insert misalignment versus cavity wall and/or versus electron beam are studied.
The CERN Resonant WISP Search (CROWS)
The subject of this work is the design, implementation and first results of the "CERN Resonant WISP Search" (CROWS), which probes the existence of Axion Like Particles and Hidden Sector Photons (HSPs) using microwave techniques. By exploiting low loss cavity resonators, multiple layers of electromagnetic shielding and a micro-Hz bandwidth detection scheme, new exclusion limits could be set. For HSPs, sensitivity was improved by a factor of 7 compared to previous laboratory experiments.
Energy-efficient, scalable and modular industrial microwave applicator for high temperature alkaline hydrolysis of PET
Microwave-assisted alkaline hydrolysis of PET can be 20 times faster and at lower temperatures. This work presents a novel industrial microwave applicator at 2.45 GHz with homogeneous distribution to support this reaction, which allows an efficient and continuous operation. In addition, an innovative dielectric and calorimetric measurements setup is presented. Furthermore, the modelling of the reaction kinetics based on the measured dielectric parameters is presented.
