Observation and evaluation of the alignment of Thomson scattering systems.

Concerning plasma diagnostics based on Thomson scattering (TS), precise adjustment and proper alignment is of great importance in order to provide reliable and accurate measurements. Any misalignment could result in an incorrectly determined plasma density or prevent the measurement with this type of diagnostic altogether. Suitable means of alignment monitoring should be integrated into each TS diagnostic system. Variations of commonly used methods are discussed in this article. Correlation of results from alignment control with performed measurements of vibrations on the COMPASS tokamak is presented. Various techniques of optimization of alignment monitoring are shown. The optimal technique, which could be accommodated during the construction of TS diagnostic systems in future fusion devices, is proposed.

High magnetic field test of the ITER outer vessel steady-state magnetic field Hall sensors at ITER relevant temperature.

The ITER outer vessel steady-state magnetic field sensor diagnostics consist of sixty sensor units. Each sensor unit features a pair of ceramic-metal Hall sensors with a sensing layer made of bismuth. The sensors were tested simultaneously in the magnetic field ranging from -12 T to +12 T at the temperature range from 27 to 127 °C. The Hall coefficient and magnetoresistance of the bismuth layer related to the sensors were identified. In the sensor operating conditions, the Hall coefficient dependence on temperature was fitted with an exponential function with a relative error of less than 0.08%, and the dependence on the magnetic field was fitted with a Gaussian-like function with a relative error of less than 0.11%. An alternative expression based on the physical understanding of the free charge carrier transport in semimetals was derived to describe the dependence of the Hall coefficient on the magnetic field, and its fitting error of 1.2 mT in terms of the magnetic field measurement has met the ITER measurement accuracy requirements.

Low cost alternative of high speed visible light camera for tokamak experiments.

We present design, analysis, and performance evaluation of a new, low cost and high speed visible-light camera diagnostic system for tokamak experiments. The system is based on the camera Casio EX-F1, with the overall price of approximately a thousand USD. The achieved temporal resolution is up to 40 kHz. This new diagnostic was successfully implemented and tested at the university tokamak GOLEM (R = 0.4 m, a = 0.085 m, B(T) < 0.5 T, I(p) < 4 kA). One possible application of this new diagnostic at GOLEM is discussed in detail. This application is tomographic reconstruction for estimation of plasma position and emissivity.

Homogeneously mixed dielectric films as double-layer antireflection coatings.

A two-layer quarter-quarter antireflection coating with a homogeneous mixture of ZnS and MgF(2) as the inner layer and MgF(2) as the outer layer was fabricated. Its transmittance was measured and found to be comparable with that of a less stable CeF(3)-MgF(2) coating. Measured peak transmittance values agree well with theoretical values.

Antireflection coatings effective at two wavelengths simultaneously in the visible region using homogeneously mixed dielectrics.

Double-layer quarter-half AR coatings effective at two wavelengths simultaneously in the visible region have been fabricated by depositing a homogeneous ZnS-MgF(2) mixture as the inner layer and MgF(2) as the outer layer. The results obtained agree well with those predicted theoretically.