A strategy to identify breakdown location in MITICA test facility: results of high voltage test campaign

The Acceleration Grid Power Supply of the MITICA test facility in Padova (Italy) is currently under commissioning. The power conversion system, the DC generator, and the High Voltage equipment have been individually commissioned, whereas the integration tests are ongoing. It is a challenging process due to the unconventional application, to the variety of different electrical technologies involved and to the complexity of the interfaces. During the integrated tests of the power supplies the achievement of 700kV stable operation has been demonstrated for the first time in a Neutral Beam Injector, but an unexpected event occurred, most likely a breakdown in the HV part, which resulted in a fault of the DC generator. A subsequent test using an auxiliary power supply was performed to check the voltage withstanding capability of the HV plant, but another breakdown occurred at around 1MV. This paper describes the activity performed to identify the location of the breakdowns affecting the integrated tests. A test campaign has been devised with increased diagnostic capabilities and specific strategy conceived to trigger intentional breakdowns in specific locations and collect measurement patterns for different cases. The results of the campaign will be presented and the current understanding of the issue will be described, with a view on future tests and further improvements of diagnostics

Overview of the design of the ITER heating neutral beam injectors

The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7MWof 1 MeVD0 or 0.87 MeVH0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam\uf0a0(NB) injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a realistic design is not possible, whereas the neutralisation ofH 12 andD 12 remains acceptable ( 4856%). The design of a long pulse negative ion based injector is inherently more complicated than that of short pulse positive ion based injectors because: \u2022 negative ions are harder to create so that they can be extracted and accelerated from the ion source; \u2022 electrons can be co-extracted from the ion source along with the negative ions, and their acceleration must be minimised to maintain an acceptable overall accelerator efficiency; \u2022 negative ions are easily lost by collisions with the background gas in the accelerator; \u2022 electrons created in the extractor and accelerator can impinge on the extraction and acceleration grids, leading to high power loads on the grids; \u2022 positive ions are created in the accelerator by ionisation of the background gas by the accelerated negative ions and the positive ions are back-accelerated into the ion source creating a massive power load to the ion source; \u2022 electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on various downstream beamline components. The design of the ITER HNBs is further complicated because ITER is a nuclear installation which will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components have to survive in that harsh environment. Additionally the beamline components and theNBcell, where the beams are housed, will be activated and all maintenance will have to be performed remotely. This paper describes the design of theHNBinjectors, but not the associated power supplies, cooling system, cryogenic system etc, or the high voltage bushingwhich separates the vacuum of the beamline fromthehighpressureSF6 of the high voltage (1MV) transmission line, through which the power, gas and coolingwater are supplied to the beam source. Also themagnetic field reduction system is not described

Correlation analysis for energy losses, waiting times and durations of type I edge-localized modes in the Joint European Torus

Several important ELM control techniques are in large part motivated by the empirically observed inverse relationship between average ELM energy loss and ELM frequency in a plasma. However, to ensure a reliable effect on the energy released by the ELMs, it is important that this relation is verified for individual ELM events. Therefore, in this work the relation between ELM energy loss (W-ELM) and waiting time (Delta t(ELM)) is investigated for individual ELMs in a set of ITER-like wall plasmas in JET. A comparison is made with the results from a set of carbon-wall and nitrogen-seeded ITER-like wall JET plasmas. It is found that the correlation between W-ELM and Delta t(ELM) for individual ELMs varies from strongly positive to zero. Furthermore, the effect of the extended collapse phase often accompanying ELMs from unseeded JET ILW plasmas and referred to as the slow transport event (STE) is studied on the distribution of ELM durations, and on the correlation between W-ELM and Delta t(ELM). A high correlation between W-ELM and Delta t(ELM), comparable to CW plasmas is only found in nitrogen-seeded ILW plasmas. Finally, a regression analysis is performed using plasma engineering parameters as predictors for determining the region of the plasma operational space with a high correlation between W-ELM and Delta t(ELM)

Effect of the relative shift between the electron density and temperature pedestal position on the pedestal stability in JET-ILW and comparison with JET-C

The electron temperature and density pedestals tend to vary in their relative radial positions, as observed in DIII-D (Beurskens et al 2011 Phys. Plasmas 18 056120) and ASDEX Upgrade (Dunne et al 2017 Plasma Phys. Control. Fusion 59 14017). This so-called relative shift has an impact on the pedestal magnetohydrodynamic (MHD) stability and hence on the pedestal height (Osborne et al 2015 Nucl. Fusion 55 063018). The present work studies the effect of the relative shift on pedestal stability of JET ITER-like wall (JET-ILW) baseline low triangularity (\u3b4) unseeded plasmas, and similar JET-C discharges. As shown in this paper, the increase of the pedestal relative shift is correlated with the reduction of the normalized pressure gradient, therefore playing a strong role in pedestal stability. Furthermore, JET-ILW tends to have a larger relative shift compared to JET carbon wall (JET-C), suggesting a possible role of the plasma facing materials in affecting the density profile location. Experimental results are then compared with stability analysis performed in terms of the peeling-ballooning model and with pedestal predictive model EUROPED (Saarelma et al 2017 Plasma Phys. Control. Fusion). Stability analysis is consistent with the experimental findings, showing an improvement of the pedestal stability, when the relative shift is reduced. This has been ascribed mainly to the increase of the edge bootstrap current, and to minor effects related to the increase of the pedestal pressure gradient and narrowing of the pedestal pressure width. Pedestal predictive model EUROPED shows a qualitative agreement with experiment, especially for low values of the relative shift

MAGNET GRID,GRILLE MAGNÉTIQUE,GRIGLIA DI MAGNETI

(EN) The invention is a new arrangement of magnets in the pattern of a geometrically symmetrical grid, lying on a plane or non-plane surface. Said arrangement produces a configuration of magnetic field that is asymmetrical with respect to the surface on which the grid lies. The magnet grid can be provided with openings for the passage of particles, gases or other fluids. The configuration does not require ferromagnetic materials but only permanent magnets or electromagnets. The asymmetry can be modified by varying the geometry of the magnets or their residual induction. (FR) L'invention porte sur un nouvel agencement d'aimants qui forme un motif de grille géométriquement symétrique reposant sur une surface plane ou non plane. Ledit agencement produit une configuration de champ magnétique qui est asymétrique par rapport à la surface sur laquelle la grille repose. La grille magnétique peut être pourvue d'ouvertures destinées au passage de particules, de gaz ou d'autres fluides. La configuration selon l'invention ne nécessite pas de matériaux ferromagnétiques, mais uniquement des aimants permanents ou des électro-aimants. On peut modifier l'asymétrie en variant la géométrie des aimants ou leur induction résiduelle. (IT) Si tratta di una nuova disposizione di magneti a forma di griglia geometricamente simmetrica, giacente su una superficie piana o non piana. Detta disposizione produce una configurazione di campo magnetico 5 dissimmetrica rispetto alla superficie su cui giace la griglia. La griglia di magneti può essere dotata di aperture per il passaggio di particelle, gas o altri fluidi. La configurazione non richiede materiali ferromagnetici, ma solamente magneti permanenti o elettromagneti. La dissimmetria può essere modificata variando la geometria dei magneti o la loro induzione residua

Interaction between molten alloys and electro-magnetic fields: levitation and cold crucible

The physics of the interaction between a liquid metals and an externally applied magnetic field is analysed starting from the basic equations of the phenomena involved: electromagnetic fields, fluid dynamics, viscosity and surface tension. A set of general equations is deduced to describe a levitation melting system. The equations are progressively simplified in order to highlight the most important contributions to the phenomena. The basis criteria for the design and operation of a cold crucible system are then described and together with some of the experimental results obtained

Method for the Identification of the Field Configuration in presence of the localized perturbation observed in RFP toroidal plasma devices

Abstract A method for the identification of the magnetic field configuration inside a RFP plasma, affected by a localized non axisymmetric perturbation, is presented. The knowledge of the magnetic field on a closed surface located around the plasma torus, together with a simplified plasma model, assure a unique solution for this inverse problem

Computation and experimental validation of the transfer functions of the local control coil system in RFX

he transfer functions required for the design of the RFX local control system of the field error at the gap were obtained from the frequency response data of Finite Elements models. Comparisons with experimental data were carried out both in the absence and in the presence of plasma. A quite satisfactory performance was observed during the firts tests of the control system