RESUMO
The measurements of the magnetic field in tokamaks such as ITER and DEMO will be challenging due to the long pulse duration, high neutron flux, and elevated temperatures. The long duration of the plasma pulse makes standard techniques, such as inductive coils, prone to errors. At the same time, the hostile environment, with repairs possible only on blanket exchange, if at all, requires a robust magnetic sensor. This contribution presents the final design of novel, steady-state, magnetic sensors for ITER. A poloidal array of 60 sensors mounted on the vacuum vessel outer shell contributes to the measurement of the plasma current, plasma-wall clearance, low-frequency MHD modes and will allow for crosscheck with the outer-vessel inductive coils. Each sensor hosts a pair of bismuth Hall probes, themselves an outcome of extensive R&D, including neutron irradiations (to 1023 n/m2), temperature cycling tests (73-473 K) and tests at high magnetic field (to 12 T). A significant effort has been devoted to optimize the sensor housing by design and prototyping. The production version features an indium-filled cell for in situ recalibration of the onboard thermocouple, vital for the interpretation of the Hall sensor measurement.
RESUMO
The WEST tokamak consists of a major upgrade of the superconducting medium size tokamak Tore Supra aiming at testing ITER divertor components. Such modification has required rebuilding a full set of magnetic diagnostics. The project was started in 2013 and completed in 2016. The diagnostic consists of a set of 469 sensors (421 pick-up coils, 36 flux loops, and 12 Rogowski coils) installed in the WEST vacuum vessel. New analog integrators have been developed in order to obtain the magnetic field and flux from the raw signal of the sensors. During the startup phase of WEST, plasma currents of the order of a few kilo amperes were measured despite much larger current of the order of hundreds of kilo amperes flowing in nearby conducting structures. The diagnostic is now fully operational and exhibits a noise level of about 0.5 mT on the magnetic field, and 2.0 mWb on flux loops allowing identifying the plasma boundary with an accuracy of a few millimeters on a 2 ms time cycle.
RESUMO
In recent years there has been a major upgrade of the JET far infrared diagnostic system consisting of a new laser system with the wavelength at 118.8 µm at and more advanced processing electronics for phase counting. This provides a second colour measurement of the electron plasma density on the vertical system. Due to the shorter wavelength, the plasma induced laser beam refraction is reduced by a factor of three alleviating density errors caused by loss of signal (so-called "fringe jumps" [A. Murari et al., Rev. Sci. Instrum. 77, 073505 (2006)]), in particular during high performance plasmas experiments in JET.
RESUMO
On the Tore Supra tokamak, a far infrared polarimeter diagnostic has been routinely used for diagnosing the current density by measuring the Faraday rotation angle. A high precision of measurement is needed to correctly reconstruct the current profile. To reach this precision, electronics used to compute the phase and the amplitude of the detected signals must have a good resilience to the noise in the measurement. In this article, the analogue card's response to the noise coming from the detectors and their impact on the Faraday angle measurements are analyzed, and we present numerical methods to calculate the phase and the amplitude. These validations have been done using real signals acquired by Tore Supra and JET experiments. These methods have been developed to be used in real-time in the future numerical cards that will replace the Tore Supra present analogue ones.
RESUMO
For the Tore Supra interferometer phase measurements, an electronics had been developed electronics using field programmable gate array processors. The embedded algorithm can correct the fringe jumps. For comparison, the electronics ran at JET during the 2009 campaign. The first analysis concluded that the electronics was not correcting all the fringe jumps. An analysis of the failures led to improvements in the algorithm, which was tested during the rest of the campaign. In this article, we evaluate the increases in the performance. From the analysis of the remaining faults, further improvements are discussed for designing future boards that are foreseen for JET using the second wavelength and the CottonMouton effect information.
