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Specific oscillations within a range of 20 kHz (“20 kHz-mode”) were investigated on the T-10 and TEXT tokamaks using Heavy Ion Beam Probe (HIBP) diagnostic. Regimes with ohmic heating on both machines, and with off-axis ECRH in T-10 were studied. It was shown that “20 kHz-modes are mainly the potential oscillations. The power spectrum of the oscillations has the form of a solitary quasi-monochromatic peak with a contrast range of (3–5). They are the manifestation of torsional plasma oscillations with poloidal wavenumber m = 0, called zonal flows. It was shown that in TEXT the radial electric field oscillations exist in a limited radial range of 0.65 > ρ < 0.95. The frequency of “20 kHz-mode” is varied in the region of observation; it diminishes to the plasma edge. In T-10, after ECRH switch-on, the frequency increases, correlating with the growth of the electron temperature Te. In both machines the frequency of the “20 kHz-mode” varies with local Te: f ∼ Te1/2, which is consistent with theoretical scaling for geodesic acoustic modes (GAM): fGAM ∼ cs/R ∼ Te1/2, where cs is the speed of sound. The absolute frequencies are close to GAM values within a factor of unity.

For the investigation of the plasma density and potential in the TJ-1 tokamak, we applied the heavy ion beam probe (HIBP) diagnostics with the beam energy up to 100 keV. The geometry of the experiment allows us to observe the whole plasma cross section and to catch the primary beam for direct calibration. HIBP on TJ-1 operates in two modes: shot-by-shot measurements which allow us to obtain the time evolution of the plasma parameters at every desired point of the detector grid, and scanning along the detector line (generally passing through the center) in the single shot which allows us to get a few profiles of the plasma parameters. When scanning we varied the injection angle with a period less than 2 ms. The spatial resolution of measurements was 2–5 mm. The bandwidth used (≈20 kHz) allows us to see the slow oscillations of the potential and density. The measurements were performed in the regimes with the magnetic fieldB=1.1–1.4 T, current I=26–32 kA, and the shot duration up to 25 ms. HIBP on TJ-1 enables us to measure simultaneously the time-spatial evolution of the potential and density; that makes HIBP a powerful tool for direct investigation of the transport processes in the plasma driven by the radial electric field.

We discuss the specific features of the application of heavy ion beam probe (HIBP) systems to tight aspect ratio tokamaks. We present and compare the HIBP projects for the TUMAN-3, GLOBUS, and COMPASS, where the inner part of the plasma is not available for regular chord diagnostics, so the HIBP becomes very desirable. All existing tight aspect ratio facilities and projects have a low (less than 1.9 T) toroidal field that requires a comparatively low beam energy range. The natural elongation and triangularity in tight aspect ratio tokamaks require an accurate calculation of the three-dimensional magnetic field for probing optimization. In comparison with traditional tokamaks, the detector grids have a wider energy interval. In general, the trajectories and detector grids for tight aspect ratio tokamaks become similar to the stellarator ones. Traditional and new probing schemes are suggested and discussed.

A heavy ion beam probe diagnostic was installed on T‐10 tokamak. Cs+ and Tl+ beams with the energy 100–280 keV and intensity about a few dozen μA 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 ω=0°–90° for B=1.5 T and Cs+ ions. High‐voltage stabilizers keep the analyzer and accelerator voltage drift on the level ΔU/U∼10−5. 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.