Nonlinear theory of mirror instability near threshold

An asymptotic model based on a reductive perturbative expansion of the drift kinetic and the Maxwell equations is used to demonstrate that, near the instability threshold, the nonlinear dynamics of mirror modes in a magnetized plasma with anisotropic ion temperatures involves a subcritical bifurcation,leading to the formation of small-scale structures with amplitudes comparable with the ambient magnetic field

Erratum: The solar orbiter radio and plasma waves (RPW) instrument (Astronomy and Astrophysics (2020) 642 (A12) DOI: 10.1051/0004-6361/201936214)

The erratum concerns Fig. 9 entitled "Antenna radio-electrical properties" for which some of the parameters are not correct. The new figure with new parameters is provided in Fig. 1 of this corrigendum. Fig. 1. Corrected Antenna radio-electrical properties. (Figure Presented)

On the temperature profile and heat flux in the solar corona: Kinetic simulations

In the solar corona the collisional mean free path λ for a thermal particle (electrons or protons) is of the order of 10-2 to 10-4 times the typical scale of variation H of macroscopic quantities like the density or the temperature. Despite the relative smallness of the ratio $\lambda/H$, an increasingly large number of authors have become convinced that the heat flux in such a plasma cannot be described satisfactorily by theories which suppose that the local particle velocity distribution functions are close to Maxwellian. We address this question through kinetic simulations of the low solar corona by assuming that non thermal velocity distribution functions are present at the base of the corona. In particular, we show that if one assumes that the electron velocity distribution functions at the base of the corona have sufficiently strong suprathermal power law tails, the heat flux may flow upwards, i.e. in the direction of increasing temperature. Using kappa velocity distribution functions as prototypes for non thermal velocity distributions, we find that the heat conduction can be properly described by the classical Spitzer & Härm (1953) law provided the kappa index is $\gtrsim 5$. This value is much smaller than the value previously found by Dorelli & Scudder (1999). In addition we show that, unless extremely strong power law tails are assumed near the base of the corona (i.e. $\kappa < 4$), a local heating mechanism (e.g. waves) is needed to sustain the temperature gradient between the base of the corona and the coronal temperature maximum

Evaluation of FET performance and restrictions by low-frequency measurements

In this paper a characterization technique for the evaluation of transistor performance and restrictions is presented, based on a simple and low-cost measurement system. Experimental examples, carried out on a 0.5 × 1000 μm2GaN HEMT, are reported. The validity of the proposed approach is demonstrated by comparing the results with the ones obtained by means of commonly adopted measurement setups

The Italian perspectives on the application of GaN technology in future SAR and RADAR systems

GaN technology providing at the same time high power density, efficiency, low noise performance combined with the robustness to high RF signals, wideband operation, represents the best solution for the development of very compact and efficient Transmit Receive (TR) Module. For this reason the Italian Space Agency (ASI) has supported the creation of a national team of competences that, starting from the availability of technological processes from the Selex ES Foundry and the experience of Thales Alenia Space Italy on SAR Systems development, promotes a European GaN technology for the next Space missions

PARASITIC EFFECTS OF BUFFER DESIGN ON STATIC AND DYNAMIC PARAMETERS OF ALGAN/GAN HIGH ELECTRON MOBILITY TRANSISTORS

GaN-based HEMTs are excellent candidates for next-generation high-power microwave applications. Nevertheless, due to the spontaneous n-type conductivity of GaN crystals, devices equipped with unintentionally-doped buffer experience detrimental short-channel effects, undermining both the device performances and their long-term stability. Technological solutions involve the introduction of carbon and/or iron compensating species which compensate the unintentional donor species, render the GaN buffer layer semi-insulating, and improve the confinement of electrons in the 2DEG. Nevertheless, the presence of foreign impurities and the related peculiar growth conditions, may give rise to enhanced crystallographic defect density. Within this work, we comprehensively investigate the static and dynamic parasitic effects related to the GaN-buffer design, and we discuss the implications on the rf performance and reliability