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We first describe the improved receiving system of the diagnostic experiment of millimeter-wave collective Thomson scattering being run on the Frascati Tokamak Upgrade (FTU), and then discuss some peculiar problems and new operating procedures related to the investigation of strong anomalous spectra of nonthermal origin, many-orders-of-magnitude stronger than the ion thermal feature merged in them, systematically observed in the experimentation, and finally ascribed to a perturbation of the gyrotron that generates the probing beam. Arguments in favor of a more general valence of the solutions actuated for the specific case of FTU are finally given. [ABSTRACT FROM AUTHOR]

Focuses on the electron cyclotron emission diagnostic of high temperature electron cyclotron resonance heated plasmas on Frascati tokamak upgrade. Accuracy of the electron temperature measurements; Comparison the accomplished measurements with Thomson scattering and observations of x-ray spectra from highly stripped molybdenum ions.

Abstract: The external walls of the Tokamak building, made of thick concrete, provide the nuclear shielding for operators working in adjacent buildings and for the environment. There are a series of openings to these external walls, devoted to ducts or pipes for ventilation, waveguides and transmission lines for heating systems and diagnostics, cooling pipes, cable trays or busbars. The shielding properties of the wall shall be preserved by adequate design of the openings in order not to affect the radiological zoning in adjacent areas. For some of them, shielding properties of the wall are not affected because the size of the network is quite small or the source is far from the opening. But for most of the openings, specific features shall be considered. Even if the approach is the same and the ways to shield can be standardized, specific analysis is requested in any case because the constraints are different. [Copyright &y& Elsevier]

Abstract: The challenge of developing the conceptual design of the ECH Upper Launcher system for MHD control in the ITER plasmas has been tackled by team of European Associations together with the European Domestic Agency (“F4E”). The launcher system has to meet the following requirements: (a) a mm-wave system extending from the interface to the transmission line up to the target absorption zone in the plasma and performing as an intelligent antenna; (b) a structural system integrating the mm-wave system and ensuring sufficient thermal and nuclear shielding; (c) port plug remote handling and testing capability ensuring high port plug system availability. The paper describes the reference launcher design. The mm-wave system is composed of waveguide and quasi-optical sections with a front steering system. An automated feedback control system is developed as a concept based on an assimilation procedure between predicted and diagnosed absorption location. The structural system consists of the blanket shield module, the port plug frame, and the internal shield for appropriate neutron shielding towards the launcher back-end. The specific advantages of a double walled structure are discussed with respect to adequate baking, to rigidity towards launcher deflection under plasma-generated loads and to removal of thermal loads, including nuclear ones. Basic studies of remote handling (RH) to validate design development are initiated using a virtual reality simulation backed by experimental validation, for which a launcher handling test facility (LHT) is set up as a full scale experimental site allowing furthermore thermohydraulic studies with ITER blanket water parameters. [Copyright &y& Elsevier]

Abstract: Suppression of plasma instabilities is a key issue to improve the confinement time of controlled thermonuclear fusion with tokamaks. Radiofrequency sources are currently used to stabilize the sawteeth and Neoclassic Tearing Modes instabilities that degrade the plasma performance. In particular, Electron Cyclotron Radiofrequency Heating (ECRH) is a suitable way to control the growth of instabilities. With this technique, in fact, it is possible to drive a localized current exactly in the narrow region of the plasma where the instabilities occur. The theory has shown the feasibility of a control strategy by means of a real-time system based on ECRH, that reduces the growth of non-linear tearing magnetic surfaces that develop into rotating island topology. This paper will show that a real-time instability control system based on the application of Electron Cyclotron Current Drive has been installed on Frascati Tokamak Upgrade (FTU) (8T magnetic field, 1.6MA plasma current), and the first tests will be presented. A typical architecture of an ECRH system devoted to the control of instabilities includes: the real-time detection of the instabilities by proper plasma diagnostics and an actively steered actuator that injects EC beams towards their target during the plasma discharge. To solve the hard real-time requirements of the actuator system, a homemade system based on a PXI embedded controller has been realized to be completely integrated into the main control system of the FTU tokamak. The system acts via the Digital Waveform Reference of the Electron Cyclotron gyrotrons and it is hardware driven by an external clock, triggers, and gates coming from a controller process of a feedback loop. [Copyright &y& Elsevier]

• Design validation of components for EC-assisted breakdown of ITER first plasma. • Updated design of the mirrors to reduce the beams envelope at the dump entrance. • Multi-bounces ray-tracing model developed for the design and assessment of the dump. • Modeling of the thermal load on the plates and the fraction of escaping power. • Study of effects of misalignment of beams and variations in the absorber thickness. First plasma operation in ITER will start after completing the assembly of the tokamak vessel and the installation of the main sub-systems, but prior to the installation of the blanket modules and the divertor cassettes. Utilization of temporary limiters and divertor replacement structures will provide a poloidal and toroidal reference side position to the plasma edge to protect the vacuum vessel and other components already installed during operations. An additional set of mirrors is required to reflect the power injected from the upper launcher towards the plasma resonance for EC-assisted breakdown of the plasma up to a beam dump needed to trap and absorb the power of the beams after crossing the plasma in order to reduce the stray radiation escaping back into the vacuum chamber down to less than 10% of the total power. The quasi-optical system has been designed, with shape and size of the mirrors compliant with the requirements provided by ITER for their installation, realization and plasma performances, resulting in two standard focussing mirrors and one grating mirror. The beam dump consists of a box with five metal plates, the first providing a spreading of the high incident power and the others coated with absorbing material with thickness distribution studied to gradually reduce the power during the multiple reflections inside the box, avoiding damages to the coating itself. This work focuses on the validation of the quasi-optical design of the mirrors and the assessment of the dump performances, based on a multi-bounces model developed ad-hoc for this purpose. The study includes a tolerance analysis for the beam dump to include the effect of uncertainties in the thickness of the absorbing coating and misalignments of the mirrors, to verify the performances of the dump also when operating in different conditions with respect to the nominal ones. [ABSTRACT FROM AUTHOR]