Articles
Publication Date: 2025
Plasma Physics and Controlled Fusion (13616587)67(10)
The linear stability of microtearing modes (MTMs) is investigated using a combination of analytical theory and gyrokinetic simulations with the gyrokinetic electromagnetic numerical experiment code. This study covers both the plasma core and pedestal regions, aiming to identify the dominant parameters affecting MTM growth rates and frequencies. Theoretical predictions and simulation results are found to be in qualitative agreement, although discrepancies appear in the collisionless limit due to factors such as the neglect of magnetic drift effects. A systematic parameter scan reveals strong dependences on collisionality, electron temperature gradients (ETGs), magnetic shear, and the Shafranov shift. Trapped particles play a dual role—destabilizing MTMs at intermediate collisionalities but reducing growth at higher values. In the pedestal, strong gradients and unfavorable magnetic geometry amplify MTM activity by nearly an order of magnitude compared to the core. While the ETG significantly increases the growth rate in the pedestal, the ion temperature gradient has only a weak stabilizing influence. These results improve the physical understanding of MTMs in realistic tokamak conditions and suggest pathways for stabilization relevant to both conventional and spherical devices. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Publication Date: 2023
Radiation Physics and Chemistry (18790895)212
FLASH radiotherapy (or FLASH-RT) is a novel radiotherapy technology consisting of radiation delivery at dose rates several orders of magnitude higher (≥40Gy/s) than the currently used in conventional clinical radiotherapy. Many recent in-vivo preclinical studies indicate that FLASH-RT can greatly spare healthy tissues while maintaining unchanged tumour control. The generally acknowledged, though not entirely substantiated, explanation for the FLASH effect relates to the oxygen depletion that occurs after the radiation passage. On the other hand, oxygen depletion or, more in general, oxygen-related effects are still not fully clarified. Different research groups carried out the Monte Carlo simulations of electron and proton irradiations in oxygenated water to evaluate the oxygen-concentration-related effects at the cell-scale level. We analysed and compared the simulation results of the oxygen effect under the FLASH condition (considering the time-dependent G-values and the oxygen enhancement ratio-weighted dose) we obtained with GEANT4-DNA against TRAX-CHEM code results in the literature. Our results indicate that oxygen depletion has a negligible effect on radiosensitivity via oxygen enhancement, showing a close agreement with the TRAX-CHEM code. The conclusion is that the Geant4-DNA toolkit can be a valid instrument to study the FLASH effect. © 2023 Elsevier Ltd
Publication Date: 2023
Scientific Reports (20452322)13(1)
A particle-in-cell simulation is modeled and run on a dusty plasma to determine the effect of the magnetic field on the process of dust-particle charging through electron–ion plasma. The electric field is solved through the Poisson equation, and the electron-neutral elastic scattering, excitation, and ionization processes are modeled through Monte Carlo collision method. The effects observed from the initial density of the plasma, the initial temperature of the electrons, and the changing magnetic field are included in this simulation model. In the dust particle charging process, saturation time and saturation charge are compared. An increase in the magnetic field does not reduce time to reach the saturation state. Determining the magnetic field boundaries which depend on the physical properties of the plasma, can be contributive in some areas of dusty(complex) plasma. The applications of the results obtained here for fusion plasma conditions and space and laboratory plasmas are discussed. The results here can be applied in future simulation models with a focus on the dust particle movement and their effect on plasma, leading to the modeling of different astrophysical plasmas thorough laboratory experiments. © 2023, The Author(s).
Publication Date: 2022
IEEE Transactions on Plasma Science (00933813)50(6)pp. 1814-1822
Graphite samples, used in first-wall and divertor of nuclear fusion reactors like tokamaks, were irradiated using hydrogen and argon ions produced in an MTPF-2 plasma focus device in 20 shots to study radiation damages. Ion energy spectra are dNH (E H)/dEH E H-2.8 with a minimum energy of 120 keV to a maximum of 1 MeV for hydrogen ions and dN Ar (E Ar) dE Ar E Ar-3.5 with a minimum energy of 200 keV and a maximum energy of 2 MeV for argon ions. Based on the results of the SRIM code, the maximum destruction of hydrogen ions is at a depth of 900 nm, and a rate of 0.025 DPA/shot and highest hydrogen density is 0.5% at 920 nm. Conversely, the highest degradation of argon ions is at a depth of 120 nm and 0.23 DPA/shot, and the highest density of argon ions at a depth of 200 nm is 0.07%. Different maximum degradation locations and the maximum density of argon ions are due to their heavy mass compared to hydrogen. SEM micrographs show holes with high population density and some sublimated areas on hydrogen-irradiated surfaces. The predominant phenomenon due to argon ion irradiation is physical sputtering, leading to cavities with a depth of several micrometers. Based on the X-ray diffraction (XRD) spectrum, the location and intensity of peaks are changed, and irradiation reduces graphitization and increases the size of the graphite crystal. © 1973-2012 IEEE.
Publication Date: 2021
IEEE Transactions on Plasma Science (00933813)49(6)pp. 1871-1876
Kinetic particle-in-cell (PIC) method is a reliable technique for the laser-plasma interactions simulation based on particles' statistical behavior. This method can be applied in simulating physical phenomena involved in optical diagnostics tools, such as the interferometry-polarimetry (IP) system. IP is one of the significant laser diagnostic methods suggested in the large tokamaks, such as international thermonuclear experimental reactor (ITER), as to improve the accuracy of density and magnetic field measurements. In this article, two separate simulations of the poloidal IP system are run by applying a 2-D/3-V XOOPIC code to observe the phase-shift and Faraday effect in a magnetized plasma with input density and poloidal magnetic field of ne =3.00× 1019 m-3 and Bp=1.00 T, respectively. For this purpose, a gaseous (CO2) linear-polarized far-infrared laser beam of λ i=118μ m wavelength, and about 30W m2 intensity is passed through the plasma, parallel to the magnetic field. The density and poloidal magnetic field are computed from laser phase-shift and Faraday rotation theories, at ne, com=2.99× 1019 m-3 and Bp, com=0.99 T, which correspond to the input values of these simulations. The obtained results indicate the competence and potency of the PIC method in simulating role-playing phenomena in ITER diagnostic devices like the IP system. © 1973-2012 IEEE.
