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This paper describes two new helical arrays of magnetic coils recently installed inside the TJ-II vacuum vessel. Their main objective is the precise measurement of the spatial periodicity of the magnetohydrodynamic perturbations usually found in the TJ-II plasmas. Given the high probability of coil failures due to the harsh plasma environment and in view of the extremely difficult access to the TJ-II vessel interior for maintenance, the coil system has been divided in two quasi-identical helical arrays. Both arrays consist of 32 triaxial sensors measuring orthogonal components of the local magnetic field along an ideal helical path whose trajectory runs close to the plasma edge. A description of the main characteristics of coils and arrays as well as their nominal positioning along an ideal helical path, inside the vessel, is given. A precise experimental determination of the real spatial orientation of the coils is performed by comparing the signals measured in current ramp-up and ramp-down experiments with calculations based on a filamentary model for the TJ-II magnetic coils. After this fine calibration procedure, it is possible to analyze the dependence of the amplitude of the measured magnetic field and its fluctuations as a function of the coil distance to the last closed flux surface. The study of the phase evolution of the parallel and perpendicular oscillatory components is also enabled. Finally, two examples of mode number determination are shown. One corresponds to a low frequency mode appearing in pure electron cyclotron resonance heating plasma, and the other one shows several modes observed during combined injection of both co and counter neutral beams and identified as shear Alfvén waves. [ABSTRACT FROM AUTHOR]

The need for a steam ingress environmental experiment is very significant to understand the impact of accidental in-vessel coolant leaks at ITER and to study the exposure of optical diagnostics to steam and humid conditions. This could happen as a result of the damage to the cooling pipes due to runaway electrons generated during plasma disruptions in ITER. In order to know the scope of this potential impact, an assessment was carried out to simulate and to study the exposure of optical elements to strong and hostile moisture conditions. After test, different measurements on optical mirrors were performed to characterize the reflectance properties, observed both in the visible and infrared spectral ranges, as well as the analysis of wavefront error, coating adherence test, and X-ray spectroscopy. Modification of properties and fluctuations in the physical behavior of optical materials and components were observed. Substrates and coatings were affected at different levels due to corrosion and oxidative depositions that modify their optical performances. In general, there are large differences in the results obtained for the same material manufactured by different manufacturing processes. Steam and humidity affected, especially substrates and metal coatings. Substrates made of silicon carbide and stainless steel were the least affected by corrosion. Rhodium coating suffered less damage than the molybdenum coating. [ABSTRACT FROM AUTHOR]

A novel magnetic configuration sweep control system for the TJ-II heliac device is described. The system is prepared to establish a reference for plasma, torus or vessel current while the coil configuration currents are swept during a single plasma discharge. It can also be run in a special simulation mode, which does not require powering the TJ-II device, intended for commissioning and experiment preparation purposes. Preliminary tests with the system have shown its ability to perform rotational transform scans while establishing a waveform for torus current independently, despite variable plasma conditions. This opens up new experimental possibilities to study the influence of rotational transform and shear independently. [ABSTRACT FROM AUTHOR]