Novel TCAD oriented definition of the off-state breakdown voltage in Schottky-gate FETs: a 4H SiC MESFET case study

Physics-based breakdown voltage optimization in Schottky-barrier power RF and microwave field-effect transistors as well as in high-speed power-switching diodes is today an important topic in technology computer-aided design (TCAD). OFF-state breakdown threshold criteria based on the magnitude of the Schottky-barrier leakage current can be directly applied to TCAD; however, the results obtained are not accurate due to the large uncertainty in the Schottky-barrier parameters and models arising above all in advanced wide-gap semiconductors and to the need of performing high-temperature simulations to improve the numerical convergence of the model. In this paper, we suggest a novel OFF-state breakdown criterion, based on monitoring the magnitude (at the drain edge of the gate) of the electric field component parallel to the current density. The new condition is shown to be consistent with more conventional definitions and to exhibit a significantly reduced sensitivity with respect to physical parameter variation

Dynamics of plasma blobs in a shear flow

The global dynamic of plasma blobs in a shear flow is investigated in a simple magnetized torus using the spatial Fourier harmonics (k-space) framework. Direct experimental evidence of a linear drift in k space of the density fluctuation energy synchronized with blob events is presented. During this drift, an increase of the fluctuation energy and a production of the kinetic energy associated with blobs are observed. The energy source of the blob is analyzed using an advection-dissipation-type equation that includes blob-flow exchange energy, linear drift in k space, nonlinear processes, and viscous dissipations. We show that blobs tap their energy from the dominant E B vertical background flow during the linear drift stage. The exchange of energy is unidirectional as there is no evidence that blobs return energy to the flow

Variety seeking behavior in the wine domain: A consumers segmentation using big data

This study investigates variety seeking behavior in the wine domain. Since variety seeking depends on brand strategies and consumers’ preferences for different types of vines and denominations, a bi-dimensional perspective is adopted. Two new variety seeking measures are defined, namely the Wine Index of Diversity and Brand Index of Diversity. A finite mixture regression model is implemented to identify and characterize groups of households sharing similar variety seeking behavior in a statistically representative sample of 8,313 Italian households. Four groups are identified based on consumer characteristics and their purchasing behavior. The largest group is “switchers,” which includes consumers showing a relatively higher wine diversity than brand diversity. Estimates reveal the “habitual” group, that lives in the southern Italy and consumes wine less frequently than all other groups. The “loyal” group includes the youngest consumers with an above average income, who reside in the northern regions. Finally, the “variety seekers” are older, have the highest incomes, and live in the central regions. This grouping provides insights into the effects of brand and wine typology on consumers’ choices

Current driven rotating kink mode in a plasma column with a non-line-tied free end

First experimental measurements are presented for the kink instability in a linear plasma column which is insulated from an axial boundary by finite sheath resistivity. Instability threshold below the classical Kruskal-Shafranov threshold, axially asymmetric mode structure and rotation are observed. These are accurately reproduced by a recent kink theory, which includes axial plasma flow and one end of the plasma column that is free to move due to a non-line-tied boundary condition.Comment: 4 pages, 6 figure

Transport equation describing fractional Lévy motion of suprathermal ions in TORPEX

Suprathermal ions, created by fusion reactions or by additional heating, will play an important role in burning plasmas such as the ones in ITER or DEMO. Basic plasma experiments, with easy access for diagnostics and well-controlled plasma scenarios, are particularly suitable to investigate the transport of suprathermal ions in plasma waves and turbulence. Experimental measurements and numerical simulations have revealed that the transport of fast ions in the presence of electrostatic turbulence in the basic plasma toroidal experiment TORPEX is generally non-classical. Namely, the mean-squared radial displacement of the ions does not scale linearly with time, but 〈r2(t)〉∼tγ , with γ �= 1 generally, γ>1 corresponding to superdiffusion and γ<1 to subdiffusion. A generalization of the classical model of diffusion, the so-called fractional L ́ evy motion, which encompasses power-law (L ́ evy) statistics for the displacements and correlated temporal increments, leads to non-classical dynamics such as that observed in the experiments. On a macroscopic scale, this results in fractional differential operators, which are used to model non-Gaussian, non-local anomalous transport in a growing number of applied fields, including plasma physics. In this paper, we show that asymmetric fractional L ́ evy motion can be described by a diffusion equation using spacefractional differential operator with skewness. Numerical simulations of tracers in TORPEX turbulence are performed. The time evolution of the radial particle position distribution is shown to be described by solutions of the fractional diffusion equation corresponding to asymmetric fractional L ́ evy motion in sub- and superdiffusive cases

Kink instabilities in jets from rotating magnetic fields

We have performed 2.5D and 3D simulations of conical jets driven by the rotation of an ordered, large-scale magnetic field in a stratified atmosphere. The simulations cover about three orders of magnitude in distance to capture the centrifugal acceleration as well as the evolution past the Alfven surface. We find that the jets develop kink instabilities, the characteristics of which depend on the velocity profile imposed at the base of the flow. The instabilities are especially pronounced with a rigid rotation profile, which induces a shearless magnetic field. The jet's expansion appears to be limiting the growth of Alfven mode instabilities.Comment: 10 pages, 13 figures, accepted for publication in A&