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.
The characteristic behaviour of breathers as well as N-order Rogue wave (RW) solution in homogeneous unmagnetized electron-positron-ion plasmas (consisting of cold ions, and isothermal Maxwellian electrons and positrons) has been studied theoretically. Nonlinear Schrödinger (NLS) equation is derived employing Krylov-Bogoliubov-Mitropolosky (KBM) perturbation technique in solving the concerned problems. The analytical solution of the NLS equation in the forms of breathers such as Akhmediev breather (AB), Kuznetsov-Ma breather (KM) solitons, as well as first-, second-, third-, and fourth-order RWs solution are obtained. The characteristic behaviour of breathers’ and their dependency on the relevant physical parameters are examined. The different orders of RWs are analyzed to obtain the region of existence of ion acoustic (IA) rogue waves (IARWs) with respect to unstable region. The potential profiles concerning different orders of RWs depend on the ratio of positron to electron concentrations ( ρ ) and wave number ( k ). Analysis reveals that the spatial difference between the two adjacent peaks of AB profiles are increasing with the enhancement of transformer physical parameter ( Λ ), while the temporal evolution between the two neighboring peaks of KM profiles decreases with increasing Λ and the amplitudes become large as well. The amplitudes of first-, second-, and third-order RWs profiles are decreasing with increasing ρ while the amplitude of fourth-order RWs profile is increasing. The results obtained in this study may be useful in understanding the propagation of nonlinear waves in optical fibers, Bose-Einstein condensates, plasma physics and atmospheric physics.
Background. The present study considers the main physicochemical parameters included in the optimum removal efficiency of carbon monoxide (CO) using the plasma-driven catalysis reactor. Material and Methods. A nonthermal plasma (NTP) –catalyst process was applied to investigate the removal efficiency of CO. The interaction of proposed factors such as; temperature, space-time, propane concentration, applied voltage, and the current was studied to estimate the optimum conditions of CO removal efficiency. Data analysis of experiments was done using General Linear Model (GLM) analysis in SPSS (version 22.0.) and fit linear regression model in MATLAB R2013a software. Results and Discussion. The results showed the interaction of temperature and space-time play a key role in CO removal (P-value <0.05). This interaction was found significantly positive with a decrease in space-time. The effect of applied voltage and current (i.e., two main parameters of power consumption) was found significant in the interaction model of C3H8/CO ratio with temperature, as well as space-time. Also, the presented regression model of results confirms the meaningful effect of interactions. Reduction of space-time is known as an energy consumption parameter controlled by reactor gap discharge, gas composition, and inner electrode material. The effect of propane presence as a reducer agent in the gas composition was found significant in the interaction model of space-time and temperature. Conclusion. Considering physicochemical parameters in designing NTP- catalyst reactors can influence energy efficiency significantly.
Plasma electromagnetic (EM) kinetic simulation faces two unavoidable difficulties. One arises from the fact that Maxwell equations determine a simultaneity relation between transverse electric field E ⃗ Tr and local growth rates of probability distribution function (PDF) f in Vlasov-Maxwell (V-M) simulation in Eulerian approach, so does that between E Tr and Lagrangian particles’ time-varying rates which refers to displacement of f -element in 6 D phase space in V-M simulation in Lagrangian approach, and macroparticles’ accelerating rates in Particle-in-Cell (PIC) simulation. These simultaneous with E Tr are termed as bottom objects’ growth rates (BOGRs) in this work. Directly solving the BOGRs needs to diagonalize a large full matrix, and hence often be approximated. The other arises from the fact that Lagrangian particles’ time-histories should uniformly converge with respect to the time-step. This severe requirement is difficult to be satisfied and hence some of Lagrangian particles’ time-histories lose fidelity. We propose a strict alternative method free from two difficulties. The initial-value problem of V-M system can be interpreted by 6 D phase space allowed deformation of an initial f -profile. By virtue of a more compact description of f , in which a conditional probability density function (C-PDF) well reflects some macroscopic conservation laws behind the V-M system, we can interpret the initial-value problem of f in terms of 6 D standing-wave oscillation in the C-PDF. A key subtle difference between microscopic scalar field and microscopic vector field can also lead to a similar scheme of particle simulation. PACS: 52.65.-y.
In this study, the influence of the position of a magnetic filter on electron temperature and hence on the negative ion density in helicon oxygen discharge is investigated. This study is performed with the view to improve negative ion density in radio frequency (RF) plasma. RF plasma is produced in the source region of Helicon Plasma Source (HeliPS) and the variation of electron temperature, density, and negative ion density in case of oxygen discharge is studied to determine the optimum position of the magnetic filter relative to the position of the antenna where RF power is applied. It is observed that the RF field can penetrate beyond the magnetic filter and cause additional ionization in the expansion chamber and thereby produce high energy electrons and decrease the negative ion density. Therefore, the position of the magnetic filter should be sufficiently away from the location of the antenna as it influences the formation of negative ions.
The objective of this study is to analyse instabilities and growth rate in unmagnetized dense non-relativistic collisionless quantum plasma under the impact of dynamics of ions. Model of quantum hydrodynamics is used to observe the streaming instabilities in highly dense inhomogeneous unmagnetized quantum plasma at low temperature. The model includes continuity and momentum equations for degenerate electrons and nondegenerate ions which interact with each other due to electrostatic field. Using normal mode analysis and linearization, perturbed potential is obtained in terms of unperturbed parameters with the help of first order perturbation in densities and velocities of electrons and ions while neglecting higher order perturbations. Variation in growth rates for detected instabilities is observed by using appropriate quantum plasma parameters.
We experimentally demonstrate nonlinear demagnification ( DM ) in plasma-based charged particle optics. The nonlinearity originates from the non-uniform penetration of electric fields through the plasma sheath region, when the object beam size ( d P ) is reduced to below the Debye length ( λ d ). The strength of nonlinearity depends upon d P and λ d , as confirmed from experimental results and a theoretical model. Nonlinear DM is unique to optics of classical Maxwell-Boltzmann systems and unrealized in conventional liquid metal sources where the Fermi Debye length ≪ d P . The realization of plasma sheaths being able to control DM can greatly enhance the performance of charged particle optical systems.
This is a Reply to the Comment of Dozias S., Pouvesle J.-M. and Robert E. on the paper ‘Mapping the electric field vector of guided ionization waves at atmospheric pressure’. The criticism in the Comment, namely that the measurements and the subsequent interpretations are wrong, seems to be invalid. Additional information will be detailed to discuss the point of view of the authors. However, the criticism raises an interesting comparison of two data sets presented in a normalized color scale. The resulting figure clearly supports the argument that the plasma-induced electric field measurements are consistent and validates the experimental investigation.
Time-varying diamagnetism in laser-produced plasma moving across a transverse magnetic field for different field strengths has been studied using fast imaging and magnetic probe. The emphasis of the present work is on the development of suitable B-dot probe, quantitative analysis of induced diamagnetic field in an expanding plasma plume and its effect on the applied magnetic field profiles. A Helmholtz coil with pulsed power system is used to produce uniform magnetic field varying from 0.13 T to 0.57 T. Helmholtz coil allows the plume imaging along the magnetic field lines, which gives the direct structural information of the induced diamagnetic cavity. A high frequency three-axis B-dot probe has been developed to measure the transient magnetic field. Different experimental approaches have been used to test the response, sensitivity and calibration of the developed probe. It has been observed that induced magnetic field displaced the external magnetic field that is plasma plume shows the diamagnetic behaviour for considered magnetic field range. The probe signals in directions orthogonal to the applied/induced magnetic lines are correlated with the distortion in applied magnetic field in three dimensional space, which is consistent with recently simulated topology of external magnetic field in similar experimental conditions [Patel et al, 2021 Plasma Phys. Control. Fusion 63 115020 ].
In the present work, we study the physicochemical changes that arise in water named plasma processed water (PPW) when it is exposed to the downstream low-pressure discharge of ammonia (NH3) gas. Optical emission spectroscopy and voltage-current characteristics of NH3 plasma are studied to identify species formed in NH3 plasma along with plasma characterization. A three-way full factorial design of experiment is performed to study the effect of process parameters named applied voltage, post-discharge gas-water interaction time, and NH3 gas pressure on physicochemical properties of PPW. The obtained results are analyzed using analysis of variance, standardized effect estimation, regression analysis, and response surfaces. The optimum values of these properties and PPW process parameters are estimated using MATLAB fmincon solver with experimental constraints. The emission spectrum of NH3 plasma showed strong intensity N2 + lines along with weak intensity N2, NH, and N+ lines. The obtained results showed the post-discharge gas-water interaction time and applied voltage had a significant impact on physicochemical properties and ammonium ions concentration in PPW. The obtained optimum value of voltage and time is 550 V and 15 min with given experimental constraints.
An atmospheric-pressure argon plasma jet featuring a novel integrated resonator-based multi-frequency impedance matching is presented and briefly characterized. Two narrow RF frequency bands can be chosen for operation or used simultaneously. This includes a mode with the higher frequency value being exactly five times the lower one. Phase-resolved optical emission spectroscopy measurements show a distinct influence of the input frequency combination on the discharge dynamics. Measurements of the dissipated electrical power and the emission spectrum for each operating mode complete the basic characterization of the device. Although it is constructively much simpler and more compact than dual-frequency discharges using a conventional impedance matching system, the presented device shows an excellent performance in dual-frequency operation.
This paper presents an analytical and simulation study of terahertz (THz) radiation generation using short, circularly polarized laser pulses propagating in plasma embedded in arbitrarily oriented magnetic field. Perturbation technique is used to obtain generated electric and magnetic wakefields within and behind the laser pulse. Coupling of components of the obliquely applied magnetic field with transverse and axial plasma electron velocities leads to the generation of linearly as well as elliptically polarized transverse electromagnetic radiation oscillating at THz frequency, under appropriate conditions. The amplitude of these fields and ellipticity of the elliptically polarized THz radiation can be varied with the help of the obliqueness of the external magnetic field. Analytical results are validated using VSim PIC simulation code.
Enhanced post-pulse electric field reversals of Ar, Xe, and XeAr mixture gases in capacitively coupled nanosecond discharges are investigated with Particle-In-Cell simulations in the context of maximizing electron density. The electric field reversal occurs at the falling edge of the voltage pulse and induces electron oscillatory movement in the plasma bulk region. The amplitude of field reversals is affected by driven voltage and the ratio of bulk length to gap distance. Exploiting the field reversal with a so called Plasma frequency dependent Square Wave (PSW) in an optimal gas mixture leads to the highest electron density. Specifically, for a 250 V PSW XeAr mixture case, the electron density is 2.2 times higher compared to a 1 kV DC pure Xe case even if the driven voltage is 4 times less than DC voltage. In 250 V PSW cases, XeAr mixture plasma has 1.2 times higher average electron density and 1.2 times electron temperature in the sheath region than a pure Xe plasma. With a narrower bulk region, the XeAr plasma has an enhanced field reversal and this leads to higher and faster growing electron density and electron temperature than a Xe plasma. For applications using Xe plasmas, XeAr mixture plasmas with PSW can be exploited for high electron density and temperature at reduced costs.
A common problem in many complex physical systems is the determination of pulsation modes from irregularly sampled time-series, and there is a wealth of signal processing techniques that are being applied to post-pulse and real-time data analysis in such complex systems. The aim of this report is studying the problem of detecting discrete spatial periodicities in the spectrum of magnetic fluctuations in tokamaks, for which the optimization of the algorithm performance is essential, particularly when multiple sensors are used with different measurement uncertainties, and some of the processed output signals are then used in real-time for discharge control. The main tool used hereafter will be the SparSpec algorithm, initially devised for astrophysical purposes and already applied to the analysis of magnetic fluctuations in various tokamaks. In its baseline version, dubbed SS-H2, the SparSpec algorithm runs in currently or previously operating tokamaks (JET, TCV and Alcator C-mod), and is foreseen to be deployed for data analysis in tokamak under construction (ITER, DTT). For JET, SS-H2 regularly runs also in real-time on a 1ms clock for detecting Alfvén Eigenmodes using synchronously-measured magnetic perturbations. On JET and TCV, it was noted that often a reduced set of sensors had to be used as the measurement uncertainties were not the same for all available sensors, somewhat deteriorating the overall performance of the algorithm. Hence, as part of a major update of the SparSpec algorithm, specifically intended for accelerating the real-time performance, use of the measurement uncertainties to weight the data, the spectral window and the ensuing penalization criterion was introduced. The behaviour of this new version of the SparSpec algorithm under a variety of simulated circumstances is analysed. It is found that the implementation of SparSpec using such error weighting produces superior results to those obtained with SS-H2, both in terms of the speed and the accuracy of the calculations. A test on actual data from the JET tokamak also shows a clear improvement in the performance of the algorithm.
Studies were carried out on the hybrid X-pinch (HXP) configuration for several wire materials using a 40 ns risetime, 300-kA pulsed-power generator with the goal of optimizing the HXP x-ray burst parameters for different applications. The gap distance between the conical electrodes of the hybrid X-pinch was varied from 0.5 to 5 mm for Al, Ag, Ti, and Mo using different wire diameters to maintain a consistent mass per unit length from one material to the next. It was found that 0.5–1 mm gap spacing was optimal to obtain a single x-ray burst, while the number of x-ray bursts increased with gap spacing for all materials at a rate of 1–2/mm. Time consistency studies of the first x-ray burst were carried out for Ti wire by changing the gap distance and wire diameter while observing the time of occurrence of the x-ray bursts. It was found that a 40 μ m Ti wire load with a 3 mm electrode gap spacing had the highest probability to have the first x-ray burst reproducibly within a 2 ns time window. Time-resolved and time-integrated diagnostics provided information about the source size, time of occurrence, intensity, and the number of the x-ray bursts.
In the present study, a series of experiments were performed to study collisions of runaway electrons in the Damavand tokamak by imaging hard x-ray radiations, as one of the secondary effects of these electrons, using radiochromic films. For these experiments, GAFCHROMIC™EBT2 dosimetry films were selected due to their high resolution imaging capability. These instruments were installed in two strip and screen structures for one- and two-dimensional imaging in high-dose areas of the Damavand tokamak, and after irradiation on the device, the recorded data were extracted using a flatbed scanner. The results showed that in runaway discharges of the Damavand tokamak, if active plasma position control system is off, predominant collision of the runaway electrons column occurs with outer wall of the vacuum chamber. Also, the recorded images indicated that dimensions of temporary sources of hard x-rays in the Damavand tokamak are about 10 cm × 10 cm. Two-dimensional imaging in these experiments showed that toroidal field coils are exposed to significant hard x-ray radiations, making the use of radiation-sensitive diagnostic systems in this area questionable. The results obtained from measurements also indicated that the highest radiation dose in the Damavand tokamak is in the limiter region and reaches up to 300 mSv shot−1.
