H. Eixenberger

Design of a digital multiradian phase detector and its application in fusion plasma interferometry

We discuss the circuit design of a digital multiradian phase detector that measures the phase difference between two 10 kHz square wave TTL signals and provides the result as a binary number. The phase resolution of the circuit is 1/64 period and its dynamic range is 256 periods. This circuit has been developed for fusion plasma interferometry with submillimeter waves on the ASDEX Upgrade tokamak. The results from interferometric density measurement are discussed and compared to those obtained with the previously used phase detectors, especially with respect to the occurrence of phase jumps. It is illustrated that the new phase measurement provides a powerful tool for automatic real-time validation of the measured density, which is important for feedback algorithms that are sensitive to spurious density signals.

Real-time feedback control of the plasma density profile on ASDEX Upgrade

The spatial distribution of density in a fusion experiment is of significant importance as it enters in numerous analyses and contributes to the fusion performance. The reconstruction of the density profile is therefore commonly done in offline data analysis. In this paper, we present an algorithm which allows for density profile reconstruction from the data of the submillimetre interferometer and the magnetic equilibrium in real-time. We compare the obtained results to the profiles yielded by a numerically more complex offline algorithm. Furthermore, we present recent ASDEX Upgrade experiments in which we used the real-time density profile for active feedback control of the shape of the density profile.

Fringe jump analysis and implementation of polarimetry on the ASDEX Upgrade DCN interferometer.

The ASDEX Upgrade tokamak is equipped with a 5-channel DCN interferometer with a probing wavelength of 195 μm. Up to now, phase measurement and density calculation have been accomplished by hard-wired phase counting electronics. Meanwhile, a fast digitizer has been installed which acquires the raw signals. That way, the various causes of counting errors by integer multiples of 2π, so-called fringe jumps, can be analyzed, and phase reconstruction schemes based on digital signal processing can be developed. In addition, a prototype polarimeter setup has been installed on one channel and allows for measurement of the Faraday rotation experienced by the probing beam.

Power inverter design for magnetic perturbation coils in nuclear fusion experiments

An economical, broad-band switched power inverter for supplying electrical current to magnetic perturbation coils in magnetic confinement nuclear fusion devices is designed and tested. The unit uses commercial IGBT blocks for a load current up to 1.3 kA at a DC-link voltage up to 500 V. Current is controlled by means of an embedded PC with real-time patched Linux operating system and commercial I/O boards. H-bridge and neutral point clamped (NPC) topologies are compared, both with standard and phase-shifted pulse width modulation (PWM). DC to 500 Hz bandwidth is demonstrated with good step response at full output current, making the system suitable for the supply of 16 in-vessel saddle coils of the ASDEX Upgrade tokamak. With multi-level topology and phase-shifted PWM the inverter design can also cover a planned additional coil set with DC to 3kHz bandwidth.

Infrared Interferometry with Submicrosecond Time Resolution in Massive Gas Injection Experiments on ASDEX Upgrade

Abstract In this paper, we describe recent measurements with the ASDEX Upgrade two-color CO2/HeNe interferometer in which a time resolution of 200 ns was obtained in the density measurement by digitizing the 40-MHz raw signals of the interferometer at 500 million samples/s and performing density reconstruction by software. It is illustrated that this high resolution is beneficial during massive gas injection for disruption mitigation, as it allows for the discovery of fast density oscillations in the frequency range from 200 kHz to ~ 1 MHz, which shows clear correlation to magnetic measurements.

BUSSARD — The high current high bandwidth multiple-phases inverter for ASDEX upgrade

The generated magnetic field of 16 coils for the control of magneto-hydrodynamic instabilities (1.3 kA each, 500 Hz bandwidth) installed into the nuclear fusion experiment ASDEX Upgrade have to be freely adjustable in space and time. Therefore, a 16-phases, fast-switching IGBT-based inverter system, dubbed BUSSARD, was designed and implemented.

A simple and versatile phase detector for heterodyne interferometers

The measurement of the relative phase of two sinusoidal electrical signals is a frequently encountered task in heterodyne interferometry, but also occurs in many other applications. Especially in interferometry, multi-radian detectors are often required, which track the temporal evolution of the phase difference and are able to register phase changes that exceed 2π. While a large variety of solutions to this problem is already known, we present an alternative approach, which pre-processes the signals with simple analog circuitry and digitizes two resulting voltages with an analog-to-digital converter (ADC), whose sampling frequency can be far below the frequency of the sinusoidal signals. Phase reconstruction is finally carried out by software. The main advantage of this approach is its simplicity, using only few low-cost hardware components and a standard 2-channel ADC with low performance requirements. We present an application on the two-color interferometer of the ASDEX Upgrade tokamak, where the relative phase of 40 MHz sinusoids is measured.

Overview Of The R&D Activities For The ITER Bolometer Diagnostic

Hans Meister∗1, H. Eixenberger1, C. Gliss1, A. Kampke1, M. Kannamüller1, J. Koll1, F. Penzel1, K. Kotrocz2, A. Pataki2, J. Szücs2, G. Veres2, T. Fekete3, L. Tatar3, P. Detemple4, K. Mpoukouvalas4 and S. Schmitt4 1 Max-Planck-Institute for Plasmaphysics, Boltzmannstr. 2, 85748 Garching, Germany 2 Wigner Research Centre for Physics, Konkoly Thege Miklós út 29-33, H-1121 Budapest, Hungary 3 Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, H-1121 Budapest, Hungary 4 Fraunhofer ICT-IMM, Carl-Zeiss-Str. 18-20, 55129 Mainz, Germany E-mail: meister@ipp.mpg.de