As human innovation continuously expands the knowledge base for life beyond Earth, the need for self-sufficient spacecraft is essential. With that, space crop production facilities are ever expanding for research and development. A current area of key interest is seed sanitation before transport from ground to the International Space Station (ISS). Sanitation practices are performed to mitigate any potential biohazard and to ensure the viability of the seed. Conventional methods involve fumigation of seeds or chemical processes but are not effective with all seed types. Therefore, plasma technology was implemented in this research to explore low-temperature plasmas as an alternative means for seed sanitation without the need for chemicals. This project investigated the viability of plasma as a means for sanitation by incorporating three different plasma types within the study. For the treatment of Cherry Belle radish seeds, the optimal system was a radio frequency (RF) sub-atmospheric plasma chamber. Treatments of 100 W for 10 min or longer with the Diener system consistently reduced microbial loads by 90% or more. While 20-min treatments caused reductions in germination rate, a treatment of 15 min with the Diener system at 100 W consistently resulted in germination rates above 80% after 1 month of seed storage. For the 5 and 10 min treatments at a pressure of 187 mTorr and power of 100 W, growth was also accelerated. Additionally, plasma provided 90% reduction of Escherichia coli and Bacillus pumilis and a 99% reduction of Fusarium ozysporum on inoculated seeds. Overall, the plasma systems show promising potential but require further exploration.
We describe a procedure to obtain the plasma parameters from the I-V Langmuir curve by using the Druyvesteyn equation. We propose to include two new parameters, q and r , to the usual plasma parameters: plasma potential ( V p ), floating potential ( V f ), electron density ( n ), and electron temperature ( T ). These new parameters can be particularly useful to represent non-Maxwellian distributions. The procedure is based on the fit of the I-V Langmuir curve with the q -Weibull distribution function, and is motivated by recent works which use the q -exponential distribution function derived from Tsallis statistics. We obtain the usual plasma parameters employing three techniques: the numerical differentiation using Savitzky Golay (SG) filters, the q -exponential distribution function, and the q -Weibull distribution function. We explain the limitations of the q -exponential function, where the experimental data V > V p needs to be trimmed beforehand, and this results in a lower accuracy compared to the numerical differentiation with SG. To overcome this difficulty, the q -Weibull function is introduced as a natural generalization to the q -exponential distribution, and it has greater flexibility in order to represent the concavity change around V p . We apply this procedure to analyze the measurements corresponding to a nitrogen N 2 cold plasma obtained by using a single Langmuir probe located at different heights from the cathode. We show that the q parameter has a very stable numerical value with the height. This work may contribute to clarify some advantages and limitations of the use of non-extensive statistics in plasma diagnostics, but the physical interpretation of the non-extensive parameters in plasma physics remains not fully clarified, and requires further research.
The solitonic and quasiperiodic structures of dust acoustic (DA) waves are investigated in a three components quantum dusty plasma composed of mobile negative dust grains, ions, and inertialess electrons. The reductive perturbation method is employed to derive A deformed Korteweg–de Vries (dKdV) equation in planar and nonplanar geometries, and its numerical solutions are obtained using the two level finite difference approximation method. The influence of geometries on DA solitons is discussed. It is observed that in nonplanar geometries, DA solitons travel at different speeds in comparison to one-dimensional planar ones. Furthermore, in the planar geometry, the bifurcation of DA traveling waves has been analyzed on the framework of the dKdV equation. By adding an external periodic force to the derived dKdV equation, the quasiperiodic behaviors of DA waves are presented.
Plasma discharges can be transient and randomly distributed where a few investigations have been carried out using laser-induced fluorescence to capture snapshots of plasma-produced radicals in the near vicinity of the discharge. Radical distribution dynamics, however, are challenging to study in situ with high spatial and temporal resolution to fully capture the interactions between the discharge and the gas. We here demonstrate a planar laser-induced fluorescence method that can capture molecular distributions of ground state hydroxyl radicals in a discharge plasma and follow how the distribution develops in time with a repetition rate of 27 kHz. The technique is demonstrated by monitoring, in real-time, how the tube-like distribution of ground state OH radicals, surrounding a gliding arc plasma, is affected by flow dynamics and how it develops as the high voltage is turned off at atmospheric pressure. The method presented here is an essential tool for capturing radical-distribution dynamics in situ of chemically active environments which is the active region of the plasma induced chemistry.
An analytical formalism to understand the impact of various parameters on evolving instabilities in inhomogeneous collisional dusty plasmas is presented here under the effect of recombination. The basic fluid dynamics for electrons and singly charged cold ions is carried out including recombination and collision at constant rate at the surface of dust particles. Dust particles are considered to be static with unperturbed density. Normal mode analysis method has been used along with linear approximation to get perturbed densities (n i1, n e1) which are used along with quasi-neutrality condition to get perturbed potential (φ1), using Poisson’s equation to obtain dispersion relation. While other authors have detected instabilities in unmagnetized plasmas, here this method has been successfully realized in presence of static magnetic field at various propagation angle and allowed the straightforward calculation of growth rates of observed instability. An extensive study of the unstable modes has been done which are well discriminated and plotted with respect to different plasma parameters like dust charge, dust density, propagation angle, magnetic field, electrostatic potential along with plasma oscillation wavelength to Debye wavelength ratio. We have observed in the said model that the presence of dust particles and propagation angle of applied magnetic field are affecting significantly the growth rate of instability as compared to magnetic field and recombination.
