arXiv subjects

M. Marin

Publications and source records attributed to M. Marin.

3 recordsLinked to original sources

arXiv2025

Far-UVC Field Emission Device at 226 nm and its Sub-Nanometer thick GaN/AlN Quantum Well Anode

We report on unique features of ultra-thin GaN/AlN quantum wells and demonstrate a new field emission device for human-safe disinfection with an external quantum efficiency of 18% and superior reliability, as compared to far-UVC LEDs. We investigate the behavior of a Shockley-Read-Hall recombination via Al vacancies-oxygen complexes in AlN barriers as a function of GaN well thickness and come to the conclusion that direct relaxation of confined states via mid-gap traps is prohibited and the main mechanism limiting the quantum efficiency (QE) is the carrier escape followed by non-radiative SRH recombination in the AlN barriers. As a consequence, the QE is highly dependent on the defect density, QW width and temperature which allowed us to reach a descent emissions at 226 nm wavelength although at wall plug efficiency being low, at 0.02%. We build a complete Light-Current-Voltage model and find that present device performance is limited by the self-heating and by the Child's space charge effect, both limitations can be easily addressed with some additional engineering efforts.

physics.optics↗

arXiv2021

First-principles-based multiple-isotope particle transport modelling at JET

Core turbulent particle transport with multiple isotopes can display observable differences in behaviour between the electron and ion particle channels. Experimental observations at JET with mixed H-D plasmas and varying NBI and gas-puff sources [M. Maslov et al., Nucl. Fusion 7 076022 (2018)] inferred source dominated electron peaking, but transport dominated isotope peaking. In this work, we apply the QuaLiKiz quasilinear gyrokinetic transport model within JINTRAC flux-driven integrated modelling, for core transport validation in this multiple-isotope regime. The experiments are successfully reproduced, predicting self consistently $ j $, $ n_{e} $, $ n_{Be} $, $ T_{e} $, $ T_{i} $, $ω_{tor}$ and the isotope composition. As seen in the experiments, both H and D profiles are predicted to be peaked regardless of the core isotope source. An extensive sensitivity study confirmed that this result does not depend on the specific choices made for the boundary conditions and physics settings. While kinetic profiles and electron density peaking did vary depending on the simulation parameters, the isotope ratio remained nearly invariant, and tied to the electron density profile. These findings have positive ramifications for multiple-isotope fuelling, burn control, and helium ash removal.

physics.plasm-ph↗

arXiv2021

Multiple-isotope pellet cycles captured by turbulent transport modelling in the JET tokamak

For the first time the pellet cycle of a multiple-isotope plasma is successfully reproduced with reduced turbulent transport modelling, within an integrated simulation framework. Future nuclear fusion reactors are likely to be fuelled by cryogenic pellet injection, due to higher penetration and faster response times. Accurate pellet cycle modelling is crucial to assess fuelling efficiency and burn control. In recent JET tokamak experiments, deuterium pellets with reactor-relevant deposition characteristics were injected into a pure hydrogen plasma. Measurements of the isotope ratio profile inferred a Deuterium penetration time comparable to the energy confinement time. The modelling successfully reproduces the plasma thermodynamic profiles and the fast deuterium penetration timescale. The predictions of the reduced turbulence model QuaLiKiz in the presence of a negative density gradient following pellet deposition are compared with GENE linear and nonlinear higher fidelity modelling. The results are encouraging with regard to reactor fuelling capability and burn control.

physics.plasm-ph↗