Sandor Zoletnik

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We describe and demonstrate a two-volume collective scattering system for localized measurements of plasma turbulence. The finite crossfield correlation length of plasma turbulence combined with spatial variations in the magnetic field direction are used to obtain spatially localized turbulence measurements at the Wendelstein 7-AS fusion experiment. By(More)
A 60 kV neutral Li beam is injected into the edge plasma of JET to measure the electron density. The beam observation system has been improved by replacing a Czerny-Turner spectrometer with a high-resolution transmission-grating spectrometer and a fast back-illuminated frame-transfer camera. The larger throughput of the spectrometer, the increased(More)
An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the(More)
In this article measurements of small scale electron density fluctuations in dithering high confinement ~H!-mode plasmas obtained by collective scattering of infrared light are presented. A scan of the fluctuation wavenumber was made in a series of similar discharges in the Wendelstein 7-AS ~W7-AS! stellarator @H. Renner et al., Plasma Phys. Control. Fusion(More)
At certain values of the edge rotational transform ιa , the confinement quality of plasmas in the Wendelstein 7-AS (W7-AS) stellarator is found to react very sensitively to small modifications of the edge rotational transform ιa . As ιa can be reproducibly changed either by external fields or by a small plasma current, these transitions offer a precise way(More)
Fusion energy research has reached a state, where a transition from laboratory scale physics experiments to industrial scale reactors is necessary and possible. Current devices can routinely reach plasma conditions needed for a fusion reactor, but positive energy balance can only be achieved by increasing the machine size by about a factor of two above the(More)
The status of the diagnostic developments for the quasistationary operable stellarator Wendelstein 7-X (maximum pulse length of 30 min at 10 MW ECRH heating at 140 GHz) will be reported on. Significant emphasis is being given to the issue of ECRH stray radiation shielding of in-vessel diagnostic components, which will be critical at high density operation(More)
A novel beam emission spectroscopy observation system was designed, built, and installed onto the Korea Superconducting Tokamak Advanced Research tokamak. The system is designed in a way to be capable of measuring beam emission either from a heating deuterium or from a diagnostic lithium beam. The two beams have somewhat complementary capabilities: edge(More)
Beam emission spectroscopy (BES) system in Korea Superconducting Tokamak Advanced Research (KSTAR) has recently been upgraded. The background intensity was reduced from 30% to 2% by suppressing the stray lights. This allows acquisition of the relative electron density profiles on the plasma edge without background subtraction from the beam power modulation(More)
The beam emission spectroscopy (BES) turbulence diagnostic on MAST is to be upgraded in June 2010 from a one-dimensional trial system to a two-dimensional imaging system (8 radial×4 poloidal channels) based on a newly developed avalanche photodiode array camera. The spatial resolution of the new system is calculated in terms of the point spread function to(More)