The Bontău Volcano, Apuseni Mts. (Romania), source for numerous debris avalanche deposits

<p>The Neogene volcanism in the western part of Romania is confined to the Apuseni Mountains and surrounding areas. The largest volcanic area is mostly developed in the WNW-ESE oriented, ca. 120 km in length Zărand-Brad-Zlatna Basin.</p><p>The Bontău Volcano (Seghedi et al., 2010) is located inside the western part of the Zărand-Brad-Zlatna Basin and it is strongly affected by erosional processes, being crossed in its northern part, from east to west, by the Crișul Alb River.</p><p>The Bontău Volcano is known to be active roughly between 14-10 Ma (according to the available K/Ar data) and it has been characterized as a composite or stratovolcano volcano associated with dome complexes, built by calc-alkaline andesitic lavas and pyroclastic deposits (andesite to basaltic andesite). The long-lasting volcanism developed in the Bontău area has a complex build up stages that we recently have found were interrupted by a series of destructive failure events. Several important volcanic collapses of the volcanic edifice took place producing large volcanic debris avalanches followed by numerous debris flows which produced various secondary volcaniclastic deposits that can be observed in different places all around the Bontău volcano. The debris avalanches deposits have not yet been known up to this study. The distribution of the debris avalanche deposits and associated volcaniclastic deposits is the main target of this study. In order to reconstruct Bontău Volcano activity and reconstruct its original morphology we done field observations and sampled the main lithologies to perform petrographic observations and geochemical and isotopic analyses (for the main lithologies).</p><p>During our field observations we tried to identify the relationships between debris avalanche deposits and older volcanic bodies (lavas, domes, volcaniclastic). One main important remark is related with the presence of several small basins at the margin of the volcano consisting of a succession of thin planar and cross-bedded sandstone in an alternation of coarse and fine layers associated with discontinuous lapilli trains (including pumices); The deposits are poorly to moderately sorted; with low angle cross lamination in lenses or pockets. Such deposits, as closely associate with debris avalanche deposits have been interpreted as small intra-hummocky basins formed after debris avalanche generation; they are mostly situated at the margins of the volcano.</p><p>The presence of multiple debris avalanche deposits can be connected with volcano growing in an extensional environment. We may assume that the long-lived Miocene rift graben system of the Zărand-Brad-Zlatna Basin experienced numerous changes in the fracture propagation and vertical movements that promoted repeated dyke intrusion and facilitated generation of numerous debris avalanches.</p><p>Acknowledgements: This work was supported by a grant of the of Ministry of Research and Innovation, CNCS – UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014, within PNCDI III.</p>

Runaway dynamics in the DT phase of ITER operations in the presence of massive material injection

A runaway avalanche can result in a conversion of the initial plasma current into a relativistic electron beam in high-current tokamak disruptions. We investigate the effect of massive material injection of deuterium–noble gas mixtures on the coupled dynamics of runaway generation, resistive diffusion of the electric field and temperature evolution during disruptions in the deuterium–tritium phase of ITER operations. We explore the dynamics over a wide range of injected concentrations and find substantial runaway currents, unless the current quench time is intolerably long. The reason is that the cooling associated with the injected material leads to high induced electric fields that, in combination with a significant recombination of hydrogen isotopes, leads to a large avalanche generation. Balancing Ohmic heating and radiation losses provides qualitative insights into the dynamics; however, an accurate modelling of the temperature evolution based on energy balance appears crucial for quantitative predictions.

New Insight into Single-Event Radiation Failure Mechanisms in Silicon Carbide Power Schottky Diodes and MOSFETs

Ion-induced leakage current degradation, and single-event burnout may be manifestestations of the same device mechanisms in both silicon carbide power diodes and MOSFETs. In all cases there is a migration of the electrical field from the front body-drain interface to the back epi-drain n+ interface, with a peak exceeding the critical electric field of silicon carbide, causing avalanche generation which enables high short-duration power densities during an approximate 20 psec window after the ion strike. The degradation effect in JBS SiC diodes seems to be independent of the length of the epitaxial region for different voltage-rated diodes.

Effect of Negative Gate Bias on Single Pulse Avalanche Ruggedness of 1.2 kV Silicon Carbide MOSFETs

When power MOSFETs experience a voltage spike initiating avalanche generation, a large amount of power is dissipated at the device junction. This leads to self-heating and lowers the threshold voltage. Some sources indicate that unintended opening of the channel creates a positive feedback, thereby increasing heat generation and leading to thermal runaway. Therefore, keeping MOSFETs off by applying a negative gate bias should improve avalanche ruggedness. In this report, this claim is investigated by comparing single pulse avalanche ruggedness of commercial 1.2 kV, 80 mΩ planar and trench MOSFETs at -10 V and 0 V off-state gate bias. Both planar and trench devices show a small increase in their breakdown voltage with negative gate bias. However, there is no significant difference in avalanche withstanding energy. Even in investigated trench gate devices where the gate oxide is susceptible to interface as well as oxide defects, keeping the gate voltage at VGS = -10 V did not result in improvements in ruggedness.

Existence of Weak Solutions to a Class of Degenerate Semiconductor Equations Modeling Avalanche Generation

We consider the drift-diffusion model with avalanche generation for evolution in time of electron and hole densitiesn,pcoupled with the electrostatic potentialψin a semiconductor device. We also assume that the diffusion term is degenerate. The existence of local weak solutions to this Dirichlet-Neumann mixed boundary value problem is obtained.