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1. Classical trajectory Monte Carlo simulation of plasma fueling using magnetic plasma expulsion

   https://doi.org/10.1063/1.5110259  

   Martinez, A.; Ordonez, C_A (July 2019, AIP Advances)

   The possibility of fueling a magnetically confined plasma using particle sources located inside of the plasma is studied by computer simulation. Magnetic plasma expulsion [R. E. Phillips and C. A. Ordonez, Phys. Plasmas 25, 012508 (2018)] would serve to keep the magnetically confined plasma away from the particle sources without adversely affecting plasma confinement. The simulations show how charged particles can be injected into a plasma by using particle sources located directly between two current-carrying wires that create a magnetic expulsion field. Plasma fueling with the average energy of injected particles greater than the average energy of plasma particles may serve for heating the plasma. Also, plasma fueling with positive and negative particles injected at different rates may serve for changing the neutrality of the plasma. Conditions for plasma fueling are investigated using a classical trajectory Monte Carlo simulation. Two types of particle sources are considered, and the fraction of emitted particles that reach (and fuel) the magnetically confined plasma is evaluated for each. 

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2. A hierarchal model for bacterial cell inactivation in solution by direct and indirect treatment using cold atmospheric plasmas

   https://doi.org/10.1088/1361-6463/ad5f3b  

   Polito, Jordyn; Kushner, Mark_J (July 2024, Journal of Physics D: Applied Physics)

   Abstract Cold atmospheric plasma devices have shown promise for a variety of plasma medical applications, including wound healing and bacterial inactivation often performed in liquids. In the latter application, plasma-produced reactive oxygen and nitrogen species (RONS) interact with and damage bacterial cells, though the exact mechanism by which cell damage occurs is unclear. Computational models can help elucidate relationships between plasma-produced RONS and cell killing by enabling direct comparison between dissimilar plasma devices and by examining the effects of changing operating parameters in these devices. In biological applications, computational models of plasma-liquid interactions would be most effective in design and optimization of plasma devices if there is a corresponding prediction of the biological outcome. In this work, we propose a hierarchal model for planktonic bacterial cell inactivation by plasma produced RONS in liquid. A previously developed reaction mechanism for plasma induced modification of cysteine was extended to provide a basis for cell killing by plasma-produced RONS. Results from the model are compared to literature values to provide proof of concept. Differences in time to bacterial inactivation as a function of plasma operating parameters including gas composition and plasma source configuration are discussed. Results indicate that optimizing gas-phase reactive nitrogen species production may be key in the design of plasma devices for disinfection. 

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3. Centrifugal-electrostatic confinement fusion

   https://doi.org/10.1063/5.0161536  

   Ordonez, C A; Weathers, D L (September 2023, Physics of Plasmas)

   A model for plasma confinement is developed and applied for describing an electrically confined thermonuclear plasma. The plasma confinement model includes both an analytical approach that excludes space charge effects and a classical trajectory Monte Carlo simulation that accounts for space charge. The plasma consists of reactant ions that form a non-neutral plasma without electrons. The plasma drifts around a negatively charged electrode. Conditions are predicted for confining a deuterium–tritium plasma using a 460 kV applied electric potential difference. The ion plasma would have a 20 keV temperature, a 1020 m−3 peak density, and a 110 keV average kinetic energy per ion (including drift and thermal portions at a certain point in the plasma). The fusion energy production rate is predicted to be 10 times larger than the energy loss rate, including contributions associated with both plasma loss to electrodes and secondary electron emission. However, an approach for enhancing the fusion power density may have to be employed to realize a practical use for centrifugal-electrostatic confinement fusion. 

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4. Wavelength scaling of electron collision time in plasma for strong field laser-matter interactions in solids

   https://doi.org/10.1038/s42005-021-00600-9  

   Nagar, Garima C.; Dempsey, Dennis; Shim, Bonggu (May 2021, Communications Physics)

   Abstract Although the dielectric constant of plasma depends on electron collision time as well as wavelength and plasma density, experimental studies on the electron collision time and its effects on laser-matter interactions are lacking. Here, we report an anomalous regime of laser-matter interactions generated by wavelength dependence (1.2–2.3 µm) of the electron collision time in plasma for laser filamentation in solids. Our experiments using time-resolved interferometry reveal that electron collision times are small (<1 femtosecond) and decrease as the driver wavelength increases, which creates a previously-unobserved regime of light defocusing in plasma: longer wavelengths have less plasma defocusing. This anomalous plasma defocusing is counterbalanced by light diffraction which is greater at longer wavelengths, resulting in almost constant plasma densities with wavelength. Our wavelength-scaled study suggests that both the plasma density and electron collision time should be systematically investigated for a better understanding of strong field laser-matter interactions in solids. 

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5. Noah Hershkowitz: Experimental plasma physics pioneer

   https://doi.org/10.1063/5.0267508  

   Severn, Greg; Baalrud, Scott_D; Foster, John (July 2025, Physics of Plasmas)

   Over a nearly 50 year career in plasma physics, spanning 1971–2020, Noah Hershkowitz designed many creative experiments that led to important contributions to plasma physics. He lived the mantra that a person who enjoys what they do will never have to work a day in their life. Noah loved plasma science. His interest was broad, encompassing fusion, low temperature, and basic plasma physics. This retrospective review discusses some highlights of his impactful contributions, focusing on diagnostics, sheath physics, and magnetic confinement for both low temperature plasma physics applications (especially cusp configurations) and fusion applications (tandem mirrors, especially axisymmetric configurations). 

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