First plasmas have been successfully achieved in the TJ-II stellarator using electron cyclotron resonance heating (f = 53.2 GHz, P ECRH = 250 kW). Initial experiments have explored the TJ-II flexibility in a wide range of plasma volumes, different rotational transform and magnetic well values. In this paper, the main results of this campaign are presented and, in particular, the influence of plasma wall interaction phenomena on TJ-II operation is discussed briefly.

A heavy ion beam probe diagnostic was installed on T-10 tokamak. Cs+ and Tl+ beams with the energy loo-280 keV and intensity about a few dozen ,uA were used. The diagnostic is able to make two-dimensional measurements of plasma parameters along the detector line, The detector grid covered the first quadrant of the plasma cross section. The measurements are possible with r/a=0.3-1, and o=O"-90" for B=lS T and Cs+ ions. High-voltage stabilizers keep the analyzer and accelerator voltage drift on the level A U/U-10m5. An absolute in situ calibration of the energy analyzer, using He target will allow to make a more accurate absolute referencing of the potential. The time dependence of the local plasma parameters was obtained. A scan along the detector line by variation of injection angle and obtaining the whole profile during one pulse is possible. The diagnostic is also sensitive to poloidal magnetic field. 0 1995 American Institute of Physics.

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...

We study Alfvén eigenmodes (AEs) in the TJ-II heliac in hydrogen plasmas heated by hydrogen co-field neutral beam injector. Taking advantage of the unique TJ-II flexibility in a varying plasma current, we have observed strong variation of the AE frequency from fAE ∼ 30 to ∼220 kHz for selected modes. An advanced heavy-ion beam probe diagnostic determines the spatial location and internal amplitudes of the modes. The modes satisfy a local AE dispersion relation including the geodesic acoustic frequency that represents the lowest frequency of the mode. Linear MHD modeling with STELLGAP and FAR3D codes shows that the calculated temporal evolution of the mode frequency reproduces the observed maxima and minima at the same time intervals with a similar frequency range, and the radial profile peaks near the outer edge of the observed one.