Parasitic Oscillations in Smooth-Wall Circular Symmetric Gyrotron Beam Ducts

In order to study parasitic oscillation that may occur in a realistic beam duct upstream to the gyrotron cavity, the self-consistent linear and spectral code TWANGlinspec has been modified. The large inhomogeneities in the smooth-wall beam duct geometry or in the magnetic field profile required the implementation of a numerical approach using a hybrid finite element method. The new model permits to characterize a large number of potentially spurious TE modes. Compared to previous studies on gyrotron beam duct instabilities, an extended interaction space including also the gyrotron cavity has been considered. The role of the connecting part between the beam duct and the cavity, called spacer, is highlighted and it is shown that the gyro backward-wave TE modes excited in this region generally have their minimum starting current. The sensitivity of the minimum starting current on electron beam velocity spread is also evaluated

High-efficiency, long-pulse operation of MW-level dual-frequency gyrotron, 84/126GHz, for the TCV Tokamak

The first unit of the dual-frequency gyrotron, 84126GHz/1MW/2s, for the upgrade of the TCV ECH system has been delivered and is presently being commissioned. During a first phase, long-pulse operation (TRF gt 0.5 mathrm{s}) has been achieved and powers in excess of 0.93MW/1.1s and 1MW/1.2s have been measured in the evacuated RF-load at the two frequencies, 84GHz (TE {17,5} mode) and 126GHz (TE {26,7} mode), respectively. Considering the different rf losses in the experimental setup, the power level generated in the gyrotron cavity is in excess of 1.1MW and 1.2MW, with a corresponding electronic efficiency of 35% and 36%. These values are in excellent agreement with the design parameters and would likely lead to a gyrotron total efficiency higher than 50% in case of implementation of a depressed collector. The gyrotron behavior is remarkably reliable and robust with the pulse length extension to 2s presently only limited by external auxiliary systems

Recent progress in the upgrade of the TCV EC-system with two 1MW/2s dual-frequency (84/126GHz) gyrotrons

The upgrade of the EC-system of the TCV tokamak has entered in its realization phase and is part of a broader upgrade of TCV. The MW-class dual-frequency gyrotrons (84 or 126GHz/2s/1MW) are presently being manufactured by Thales Electron Devices with the first gyrotron foreseen to be delivered at SPC by the end of 2017. In parallel to the gyrotron development, for extending the level of operational flexibility of the TCV EC-system the integration of the dual-frequency gyrotrons adds a significant complexity in the evacuated 63.5mm-diameter HE11 transmission line system connected to the various TCV low-field side and top launchers. As discussed in [1], an important part of the present TCV-upgrade consists in inserting a modular closed divertor chamber. This will have an impact on the X3 top-launcher which will have to be reduced in size. For using the new compact launcher we are considering employing a Fast Directional Switch (FADIS), combining the two 1MW/126GHz/2s rf-beams into a single 2MW rf-beam

Etude de faisabilité d’une valorisation de 10 bâtiments de l’Etat du Valais avec de la consommation propre

Apporter des recommandations chiffrées concernant la production d’énergie photovoltaïque sur certains bâtiments de l’Etat du Valais

Evaluation of experimentally measured non-stationary oscillations in gyrotrons using adequate simulation methods

In order to properly simulate cases in which gyrotrons exhibit fast temporally varying oscillations, such as non-stationary oscillations or possible dynamic After-Cavity Interaction (ACI), an adequate model for the beam-wave interaction has to be used. We will show that the commonly used assumption of considering a constant wave-field envelope during the electron transit time has to be abandoned. The appropriate model (reduced 1D Particle-In-Cell (PIC) model) is briefly presented and the implications of using an inadequate model are illustrated. For the case of a 150W/260GHz gyrotron, non-stationary simulations with the new model will be compared to experiment and used in order to investigate the underlying mechanism of these oscillations

Salicylic acid production in response to biotic and abiotic stress depends on isochorismate in Nicotiana benthamiana

Salicylic acid (SA) is an important signal involved in the activation of defence responses against abiotic and biotic stress. In tobacco, benzoic acid or glucosyl benzoate were proposed to be precursors of SA. This is in sharp contrast with studies in Arabidopsis thaliana, where SA derives from isochorismate. We have determined the importance of isochorismate for SA biosynthesis in Nicotiana benthamiana using virus-induced gene silencing of the isochorismate synthase (ICS) gene. Plants with silenced ICS expression do not accumulate SA after exposure to UV or to pathogen stress. Plants with silenced ICS expression also exhibit strongly decreased levels of phylloquinone, a product of isochorismate. Our data provide evidence for an isochorismate-derived synthesis of SA in N. benthamian

Overview on recent progress in magnetron injection gun theory and design for high power gyrotrons

The magnetron injection gun (MIG) is one of the most critical subcomponents in gyrotrons. The electron beam, which has the primary role on the gyrotron operation, is generated and configured at this part of the tube. The electron beam properties determine the excitation mode in the cavity, the power of the generated microwaves and the gyrotron efficiency. The operation of MIGs could be influenced by several factors such as trapped electrons, manufacturing tolerances, roughness of the emitter ring, emitter temperature inhomogeneity, electron beam neutralization effect, etc. The influence of many of these factors on the electron beam quality has been systematically investigated during the last years. Several novelties have been proposed in order to limit the influence of these factors on the gyrotron operation. In particular, new design criteria have been proposed for the suppression of electron trapping mechanisms, a new type of the emitter ring has been proposed to minimize the influence of the manufacturing tolerances and edge effects on the beam quality, alternative MIG design approaches have been proposed, etc. An overview of all these works will be presented here