1,721,029 research outputs found
RFX first wall thermal power handling: 3D numerical models and experimental validations
No full textOne of the emerging issues for future thermonuclear devices is the non-uniform power deposition on the first wall or divertor surfaces. The localized peaks of power are detrimental both for the lifetime of the plasma facing components and for plasma heating and confinement. The thermal monitoring of the first wall can be done with temperature measurements acquired during the experiments by means of thermocouples and/or infrared camera images. If the measurement system is integrated with analytical or numerical models, it is possible to estimate the applied thermal loads and to obtain a thorough knowledge of the thermal behaviour of the first wall and vacuum vessel system. The numerical model developed for the RFX machine is hereby described and validated by means of comparisons with IR camera and thermocouple temperature measurements
Distribution of the background gas in the MITICA accelerator
No full textMITICA is the ITER neutral beam test facility to be built in Padova for the generation of a 40A D- ion beam with a 16×5×16 array of 1280 beamlets accelerated to 1MV. The background gas pressure distribution and the particle flows inside MITICA accelerator are critical aspects for stripping losses, generation of secondary particles and beam non-uniformities. To keep the stripping losses in the extraction and acceleration stages reasonably low, the source pressure should be 0.3 Pa or less. The gas flow in MITICA accelerator is being studied using a 3D Finite Element code, named Avocado. The gas-wall interaction model is based on the cosine law, and the whole vacuum system geometry is represented by a view factor matrix based on surface discretization and gas property definitions. Pressure distribution and mutual fluxes are then solved linearly. In this paper the result of a numerical simulation is presented, showing the steady-state pressure distribution inside the accelerator when gas enters the system at room temperature. The accelerator model is limited to a horizontal slice 400 mm high (14 of the accelerator height). The pressure profile at solid walls and through the beamlet axis is obtained, allowing the evaluation and the discussion of the background gas distribution and nonuniformity. The particle flux at the inlet and outlet boundaries (namely the grounded grid apertures and the lateral conductances respectively) will be discuss
Ricerca e sviluppo di diagnostiche magnetiche per ITER
No full textE' attualmente in fase di progettazione e sviluppo a Padova una parte rilevante del sistema di diagnostiche magnetiche da installare nel reattore sperimentale a fusione ITER. Tale sistema di misura sarà usato per il controllo della forma e della posizione del plasma e dovrà garantire adeguata precisione ed affidabilità anche in esperimenti di durata molto lunga (fino a 1 ora).
I sensori di tale sistema, in particolar modo quelli più vicini al plasma (sensori “in-vessel”), devono funzionare in ambiente particolarmente ostile per il vuoto, l'alta temperatura, l'alto flusso di radiazioni neutroniche che producono ulteriore riscaldamento e anche trasmutazione dei materiali. Per tale ragione si usano sensori magnetici tipo induttivo (detti "pick-up coils"), che sono gli unici in grado di resistere a tale ambiente. Tuttavia le forze elettromotrici di origine termoelettrica o nucleare che si possono manifestare nei conduttori che costituiscono i sensori [1,2,3] in possono pesantemente inficiare la precisione delle misure. Infatti la presenza di pur deboli forze elettromotrici spurie nel sensore provoca una inevitabile deriva nella misura del campo magnetico, che viene ottenuta integrando nel tempo il segnale di uscita del sensore stesso. Per ridurre quanto più possibile le forze elettromotrici spurie, sono stati studiati e proposti dei sensori di campo magnetico a basso gradiente termico, il cui avvolgimento è realizzato utilizzando dei cavi flessibili ad isolamento ceramico aventi un diametro di 0.55mm. Tale avvolgimento è inoltre impregnato con della ceramica liquida (successivamente solidificata mediante un opportuno processo di riscaldamento) per garantire una adeguata trasmissione del calore.L’attività di R&D prevede le seguenti attività:
1. progettazione e sviluppo di un sistema di impregnazione
2. verifica delle proprietà elettriche dei conduttori (si tratta infatti di conduttori molto delicati, per l’esiguo spessore dell’isolamento ceramico flessibile ≈ 0.01 mm).
3. test sui provini per evidenziare i punti critici e migliorare il processo di impregnazione mediante:
• prove di stress termico e meccanico, sezionamento dei provini.
• prove termiche per verificare la conduttanza termica dell’insieme dell'avvolgimento.
• prove magnetiche per verificare la sensibilità del sensore, la banda passante e l'immunità ai campi trasversali
Lo sviluppo dei prototipi dei sensori è tuttora in corso ed in fase di affinamento
Development and Testing of in-Vessel Equilibrium Pick-up Coils for ITER
No full textA new concept of magnetic pick‐up coil has been developed, aimed at reducing radiation induced thermoelectric effects which could affect the quality of the signals of the magnetic diagnostic for ITER. A winding made of a ceramic‐coated conductor and impregnated with ceramic filler is proposed as an alternative to the Mineral Insulated Cable, presently indicated in ITER reference design. Some prototypes of the new in‐vessel pick‐up coils have been designed, built and tested, to assess the thermoelectric characteristics of the coils
Colangite sclerosante primitiva: imaging CT e RM morfo-funzionale con mezzi di contrasto epatobiliari
No full textDevelopment of an image recognition system for RFX first wall maintenance
No full textSince the beginning of the machine operation a remote handling system (RHS) has been used to carry out maintenance tasks inside the RFX vacuum vessel, such as tile replacement, first wall inspection and graphite fragment removal. In order to speed up the tile replacement operations and to increase their reliability and safety, it was envisaged to develop a monoscopic vision system capable of recognizing the tile clamping system components on which the end-effector must act to dismount/mount the tiles. The vision system has now been realized and it is described in the paper along with end-effector modifications and executed tests
Design of a new toroidal shell and support structure for RFX
No full textThe physics results obtained from RFP experiments at high current (0.8–1 MA) indicate the need for a better control of the plasma MHD modes, which grow rapidly and lock to the wall during the pulse. The modifications planned for the RFX machine have been designed to guarantee both a passive and an active control of these modes. The present 65 mm thick aluminium shell will be replaced by a 3 mm thick copper shell which is assembled on the vacuum vessel, closer to the plasma edge. In addition 192 saddle coils will be installed to actively control the main mode spectrum of RFX. As a result of these modifications, a new toroidal support structure will be required, which carries out the mechanical functions of the previous shell and supports the new saddle coils. This paper deals with the design of the thin shell and toroidal structure. The solutions which guarantee the required safety level, from a mechanical and thermal point of view, and the technological details of the electrical insulation systems for the various components are highlighted
- …
