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As part of the EUROfusion project, the conceptual design of a 1 MW 236 GHz hollow-cavity gyrotron is ongoing at IHM, KIT for a DEMOnstration Power Plant (DEMO), along with a 2 MW coaxial-cavity design concept. Fast frequency-tunable gyrotrons (tuning within a few seconds) are recommended for plasma stabilization using a non-steerable antenna. In this work, the mode-selection approach for such a frequency-tunable gyrotron is presented and suitable operating modes for fast frequency tunability are suggested. Magnetic field tuning has been studied as an effective technique to tune the gyrotron operating frequency. The step-tunability of the 236 GHz gyrotron within the frequency range of ±10 GHz in steps of 2–3 GHz is demonstrated in numerical simulations. A hybrid-type Quasi-Optical Launcher (QOL) has been designed for a step-frequency tunable gyrotron with sufficiently high Fundamental Gaussian Mode Content (FGMC).

AbstractThe European Union is working toward providing 2-MW, coaxial-cavity, continuous-wave (cw) 170-GHz gyrotrons for ITER. Their design is based on results from an experimental preprototype tube having a pulse length of several milliseconds, in operation at Forschungszentrum Karlsruhe (FZK) for several years now. The first industrial prototype tube was designed for cw operation but, in a first phase, aimed at a pulse length of 1 s at the European Gyrotron Test Facility in Lausanne, Switzerland, as part of a phased testing/development program (1 s, 60 s, cw). The first experimental results of the operation of this prototype gyrotron are reported here. The microwave generation was characterized at very short pulse length (<0.01 s) using a load on loan from FZK, and the highest measured output power was 1.4 MW, at a beam energy significantly lower than the design value (83 kV instead of 90 kV), limited by arcing in the tube. The radio-frequency (rf) beam profile was measured to allow reconstruction of the phase and amplitude profile at the window and to provide the necessary information permitting proper alignment of the compact rf loads prior to pulse extension. Arcs in the tube limited the pulse length extension to a few tens of milliseconds. According to present planning, the tube is going to be opened, inspected, and refurbished, depending on the results of the inspection, to allow testing of an improved version of the mode launcher and replacement of some subassemblies.

Numerical modelling of an electron gun in the space charge limited regime requires determining the current density distribution as well as the electric fields and electron trajectories. This is a rather complicated self-consistent problem, since the space charge influences the electric field, which in turn influences the electron trajectories. Previous simulations of magnetron electron guns using the BFCPIC and BFCRAY codes used a simple emission model (constant current density) that is approximately valid for thermionic emission. The code has been modified to include space charge limited emission. Several different ways of doing this are considered.

Introduction:Accumulating evidence suggests that increased aortic pulse wave velocity (PWVa; gold standard measure of arterial stiffness) is associated with cardiovascular morbidity and mortality. However, there is paucity in the literature documenting optimal PWV cut-off points in asymptomatic patients with carotid atherosclerosis. Accordingly, the objective of the present study was twofold 1) to examine the link between vascular calcification measured as carotid plaque and arterial stiffness, and 2) to find an optimal threshold of PWVa implying vascular calcification.Methods:On a cross sectional design fashion we tested patients who visited our outpatient department by their own initiative for a cardiovascular check-up. Both extracranial carotid systems were screened. The results were considered to be positive for asymptomatic atherosclerosis if > 1 mm echogenic (calcified) plaque was seen and/or > 1.3 mm IMT was measured. Carotid calcification and PWVa were measured via ultrasound (HP Sonos 2000, USA) and a validated oscillometric device (Arteriograph; Hungary), respectively.Results:A total of 643 (F= 365) subjects were evaluated in this study with 16% smokers and 49% displayed carotid atherosclerosis. Subject characteristics were age (M ? SD) 57.2 ? 11.2 yrs, heart rate 71.9 ? 10.7 beats/min, systolic blood pressure (BP) 134.1 ? 17.6 mmHg, diastolic BP 81.6 ? 9.9 mmHg, and PWVa 10.0 ? 2.2 m/sec. Logistic Regression models found that PWVa was an independent positive predictor (P <0.001) of carotid plaque even after controlling for BP and age. To evaluate the model and sensitivity of PWVa for predicting carotid plaque a standard ROC curve was plotted. It was calculated that the optimal threshold of PWVa for predicting vascular calcification proved to be 9.3 m/sec with a sensitivity of 76.5% and a specificity of 65.5%.Conclusions:Results demonstrate that PWVa is associated with vascular calcification measured as carotid plaque. In addition, the ROC calculated cutoff point of PWVa at 9.3 m/sec to detect those patients at risk may have significant clinical implications. Prospective studies aimed at identifying patients at risk using non-invasive PWVa measurements as well as proposing preventive measures in those with high PWVa are warranted.