Search results for "Inventio"

Multi-pulse characterization of trapping/detrapping mechanisms in AlGaN/GaN high electromobility transistors

2019

GaN high-electro mobility transistors (HEMTs) are among the most promising candidates for use in high-power, high-frequency, and high-temperature electronics owing to their high electrical breakdown threshold and their high saturation electron velocity. The applications of these AlGaN/GaN HEMTs in power converters are limited by the surface trapping effects of drain-current collapse. Charge-trapping mechanisms affect the dynamic performance of all GaN HEMTs used in power switching applications. This study analyzes the dynamic resistance of GaN HEMTs and finds that the effects of dynamic resistance can be suppressed by controlling switching conditions and on-off cycles.

Crystalline phase detection in glass ceramics by EPR spectroscopy

2018

The advances of EPR spectroscopy for the detection of activators as well as determining their local structure in the crystalline phase of glass ceramics is considered. The feasibility of d-element (Mn2+, Cu2+) and f-element (Gd3+, Eu2+) ion probes for the investigation of glass ceramics is discussed. In the case of Mn2+, the information is obtained from the EPR spectrum superhyperfine structure, for Gd3+ and Eu2+ probes – from the EPR spectrum fine structure, whereas for Cu2+ ions the changes in the EPR spectrum shape could be useful. The examples of EPR spectra of the above-mentioned probes in oxyfluoride glass ceramics are illustrated. ----/ / /---- This is the preprint version of the fol…

Power efficiency improvements with the radio frequency H− ion source

2016

CW 13.56 MHz radio frequency-driven H(-) ion source is under development at the University of Jyväskylä for replacing an existing filament-driven ion source at the MCC30/15 cyclotron. Previously, production of 1 mA H(-) beam, which is the target intensity of the ion source, has been reported at 3 kW of RF power. The original ion source front plate with an adjustable electromagnet based filter field has been replaced with a new front plate with permanent magnet filter field. The new structure is more open and enables a higher flux of ro-vibrationally excited molecules towards the plasma electrode and provides a better control of the potential near the extraction due to a stronger separation …

New progress of high current gasdynamic ion source (invited).

2016

The experimental and theoretical research carried out at the Institute of Applied Physics resulted in development of a new type of electron cyclotron resonance ion sources (ECRISs)—the gasdynamic ECRIS. The gasdynamic ECRIS features a confinement mechanism in a magnetic trap that is different from Geller’s ECRIS confinement, i.e., the quasi-gasdynamic one similar to that in fusion mirror traps. Experimental studies of gasdynamic ECRIS were performed at Simple Mirror Ion Source (SMIS) 37 facility. The plasma was created by 37.5 and 75 GHz gyrotron radiation with power up to 100 kW. High frequency microwaves allowed to create and sustain plasma with significant density (up to 8 × 1013 cm−3 ) …

2020

Time-resolved photoemission with ultrafast pump and probe pulses is an emerging technique with wide application potential. Real-time recording of nonequilibrium electronic processes, transient states in chemical reactions, or the interplay of electronic and structural dynamics offers fascinating opportunities for future research. Combining valence-band and core-level spectroscopy with photoelectron diffraction for electronic, chemical, and structural analyses requires few 10 fs soft X-ray pulses with some 10 meV spectral resolution, which are currently available at high repetition rate free-electron lasers. We have constructed and optimized a versatile setup commissioned at FLASH/PG2 that c…

Atomic, electronic and magnetic structure of an oxygen interstitial in neutron-irradiated Al2O3 single crystals

2020

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under Grant Agreement No. 633053 and Enabling Research project: ENR-MFE19.ISSP-UL-02 “Advanced experimental and theoretical analysis of defect evolution and structural disordering in optical and dielectric materials for fusion application”. The views and opinions expressed herein do not necessarily reflect those of the European Commission. In addition, the research leading to these results has received funding from the Estonian Research Council grant (PUT PRG619).

A New Multipactor Effect Model for Dielectric-Loaded Rectangular Waveguides

2019

Multipactor is an electron discharge that may appear in particle accelerators and microwave devices such as filters, multiplexers, and RF satellite payloads in satellite on-board equipment under vacuum conditions. When some resonance conditions are satisfied, secondary electrons get synchronized with the RF fields, and the electron population inside the device grows exponentially leading to a multipactor discharge. This multipactor discharge has some negative effects that degrade the device performance: increase of signal noise and reflected power, heating of the device walls, outgassing, detuning of resonant cavities, and even the partial or total destruction of the component. The main aim…

Comparative study of the luminescence properties of macro- and nanocrystalline MgO using synchrotron radiation

2013

MgO nano-powder with an average crystallite size of nanoparticles ranging 10-15 nm was synthesized using the extractive-pyrolytic method and was studied by room temperature VUV spectroscopy under synchrotron radiation excitation. Comparative analysis of their luminescent properties with that of mac- rocrystalline powder analogues and an MgO single crystal, grown by the arc-fusion method, has been per- formed under excitation by pulsed VUV synchrotron radiation. Special attention was paid to VUV spectral range, which is not reachable with commonly used lamp and laser sources. A considerable blue shift of about 0.3 eV in the excitation spectra of 2.95 eV emission band, was revealed in nanocry…

Creation and thermal annealing of structural defects in neutron-irradiated MgAl 2 O 4 single crystals

2018

Abstract Several novel hole-type defects (a hole localized at a regular oxygen ion near a negatively charged structural defect) have been revealed in fast neutron irradiated MgAl2O4 crystals using the EPR method. The pulse annealing of the EPR signal of these centers was compared to that of radiation induced optical absorption in the same crystals. Taking into account the determined models of V1, V2 and V22 paramagnetic centers, the tentative scenario of the thermal annealing process of neutron-induced defects (hole-type and complementary electron F-type ones) is proposed. In addition, one more paramagnetic hole center consisting of an Al|Mg as-grown antisite defect near an aluminum vacancy…

EPR and optical spectroscopy of neutron-irradiated Gd3Ga5O12 single crystals

2020

Abstract In this paper, we have performed comparative analysis of EPR, optical absorption (OA) and luminescence spectra for a series of Gd3Ga5O12 (GGG) single crystals irradiated with fast neutrons with fluencies varied from 1016 to 1020n/cm2. In a crystal irradiated with the maximum neutron fluence, the EPR spectra demonstrated the formation of several paramagnetic defects. In particular, EPR spectrum shows a strong resonance at (effective) g ≈ 1.4 with practically isotropic behavior in the crystal rotation around the [1 1 1] direction (magnetic field being perpendicular to [1 1 1]) and several weaker lines in the g ≈ 1.1–2.6 region, which show more pronounced angular dependences. While th…