RESUMEN
Remote control of the diagnostic systems is the basic requirement for the high performance plasma operation in a fusion device. This work presents the development of the remote control system for the multichannel Doppler backward scattering (DBS) reflectometers. It includes a remote controlled quasi-optical system and a remote intermediate frequency (IF) amplifier gain control system. The quasi-optical system contains a rotational polarizer, its polarization angle is tunable through a remote controlled motor, and it could combine the microwave beams with a wide frequency range into one focused beam. The remote IF gain control system utilizes the digital microcontroller (MCU) technique to regulate the signal amplitude for each signal channel. The gain parameters of amplifiers are adjustable, and the feedback of working status in the IF system will be sent to MCU in real time for safe operation. The gain parameters could be controlled either by the Ethernet remote way or directly through the local control interface on the system. Preliminary experimental results show the effectiveness of the remote controlled multichannel DBS system.
RESUMEN
A newly upgraded correlation electron cyclotron emission (CECE) diagnostic has been installed on the ASDEX Upgrade tokamak and has begun to perform experimental measurements of electron temperature fluctuations. CECE diagnostics measure small amplitude electron temperature fluctuations by correlating closely spaced heterodyne radiometer channels. This upgrade expanded the system from six channels to thirty, allowing simultaneous measurement of fluctuation level radial profiles without repeat discharges, as well as opening up the possibility of measuring radial turbulent correlation lengths. Newly refined statistical techniques have been developed in order to accurately analyze the fluctuation data collected from the CECE system. This paper presents the hardware upgrades for this system and the analysis techniques used to interpret the raw data, as well as measurements of fluctuation spectra and fluctuation level radial profiles.
RESUMEN
Turbulent temperature fluctuations are measured on the ASDEX Upgrade tokamak using pairs of closely spaced, narrow-band heterodyne radiometer channels and a standard correlation technique. The pre-detection spacing and bandwidth of the radiometer channel pairs is chosen such that they are physically separated less than a turbulent correlation length, but do not overlap. The radiometer has 4 fixed filter frequency channels and two tunable filter channels for added flexibility in the measurement position. Relative temperature fluctuation amplitudes are observed in a helium plasma to be δT/T = (0.76 ± 0.02)%, (0.67 ± 0.02)%, and (0.59 ± 0.03)% at normalised toroidal flux radius of ρtor = 0.82, 0.75, and 0.68, respectively.
RESUMEN
Recent measurements of microwave and x-ray emission during edge localized mode (ELM) activity in tokamak plasmas provide a fresh perspective on ELM physics. It is evident that electron kinetics, which are not incorporated in standard (fluid) models for the instability that drives ELMs, play a key role in the new observations. These effects should be included in future models for ELMs and the ELM cycle. The observed radiative effects paradoxically imply acceleration of electrons parallel to the magnetic field combined with rapid acquisition of perpendicular momentum. It is shown that this paradox can be resolved by the action of the anomalous Doppler instability which enables fast collective radiative relaxation, in the perpendicular direction, of electrons accelerated in the parallel direction by inductive electric fields generated by the initial ELM instability.