The theoretical properties of electron Bernstein wave (EBW) plasma heating in the TJ-II stellarator are presented in this work. Previous studies carried out in this device have demonstrated that the O–X–B mode conversion at the fundamental electron cyclotron harmonic is the best scenario for plasma heating. This scheme presents high absorbed power for central densities above 1.2 × 1019 m−3 and has no upper density limit. In this paper, the ray tracing code TRUBA has been used in its non-relativistic modality to optimize the power injection position and to design a launching system that provides the optimum theoretical results. The main characteristics of the system, whose final design is based on the former calculations, are described. To explore the importance of relativistic effects and to compare them with the non-relativistic calculations, the weakly relativistic dispersion relation, valid for and thus suitable for EBW at low cyclotron harmonics, has been obtained and included in TRUBA. Although they are of little importance for the optimization calculations, the relativistic effects are shown to be not negligible both in the ray trajectories and in the power absorption estimations for temperatures above 1 keV.

The study of the properties of edge plasma, in particular , the plasma rotation speed, in toroidal traps is associated with the search for ways to increase the efficiency and reliability of the thermonuclear reactor. One of the methods for measuring the rate of poloidal plasma rotation in tokamaks and stellarators is Doppler reflectometry (DR). The Doppler reflectometer is designed to work as part of the experimental L-2M device to measure the rates of its poloidal rotation, as well as to measure the spatial-frequency spectra of plasma density fluctuations [1]. Diagnostics of high-temperature plasma in magnetic confinement systems is associated with a variety of problems and requires atypical engineering solutions. The powerful sources of microwave radiation (gyrotrons) used to heat the plasma [2] interfere with the detection of low-power diagnostic signals. To isolate such signals, it is necessary to provide high suppression at the ECR frequency of heating 75 GHz and to provide low attenuation at the diagnosis frequency of 30-40 GHz. The created system for filtering electromagnetic radiation consists of a band-stop filter based on a Fabry-Perot resonator and three, pin-shaped waveguide filters [3]. The CAD EMPro Keysight Technologies in a three-dimensional geometry of band-stop filter was represented as a few pairs of contiguous mica plates arranged successively at a distance from each other. Simulation of a microwave filter based on a Fabry-Perot resonator for microwave diagnostics of Doppler reflectometry, made it possible to construct an experimental filter sample with characteristics close to the given ones. The report presents the results of the development , modeling and experimental study of a filter based on a Fabry-Perot (FP) resonator. The introduction of the filter system made it possible to successfully carry out experimental measurements of the spectra of DR in the L-2M stellarator with an ECR heating power density of up to 3.4 MW/m 3. The aim of the research was to create conditions for the stable operation of DR in conditions of powerful heating ECR radiation. To reduce the effect of an external signal with a frequency of 75.3 GHz and noise in the range 60-80 GHz, it was necessary to create a new filtering system. In the filtration system we used band-stop filters. The task of these filters is to provide large attenuation (suppression) in a certain frequency range Δf near the central frequency f 0. The system of filters for diagnostics of DR consists of three pin-waveguide filters and filter based on Fabry-Perot resonator made of mica plates. In view of the design features of the diagnostics (in particular, the overall dimensions of the waveguide paths) the installation of additional pin filters, was not possible. It was required to design and manufacture a compact band-stop filter with a central suppression frequency of 75 GHz. A filter was proposed from the sequence of Fabry-Perot resonators. Millimeter and submillimeter filters based on the Fabry-Perot resonator are actively used in various di...

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Abstract.In the present work, we have compared different linear methods to estimate the Electron Bernstein Current Drive (EBCD). The expressions for the current drive efficiency have been plugged to the ray tracing code TRUBA, which was used in previous works for EBW heating studies in the TJ-II stellarator. This device is taken here as an example for this comparison.The driven current is calculated for different densities and temperatures, as well as launching directions of the heating beam, which is a critical issue in the O-X-B mode conversion scenario considered in TJ-II. The range of applicability of each model is discussed. The influence of the Ohkawa, relativistic and frictional trapping effects on the total current generated is studied by comparing the results obtained by pairs of models that include and neglect those effects. The Ohkawa effect has resulted to be the less important. Although the relativistic effects are not negligible, the main disagreement between the results arises from including or not momentum conservation and neglecting frictional trapping effects. The total EBCD current drive efficiency calculated is in all cases greater than the experimental ECCD one, previously measured in TJ-II. The results presented in this work are the guideline for future experiments in this device.