Investigation of light ion fusion reactions with plasma discharges
T. Schenkel, A. Persaud, H. Wang, P. A. Seidl, R. MacFadyen, C. Nelson, W. L. Waldron, J. -L. Vay, G. Deblonde, B. Wen, Y. -M. Chiang, B. P. MacLeod, Q. Ji
The scaling of reaction yields in light ion fusion to low reaction energies is important for our understanding of stellar fuel chains and the development of future energy technologies. Experiments become progressively more challenging at lower reaction energies due to the exponential drop of fusion cross sections below the Coulomb barrier. We report on experiments where deuterium-deuterium (D-D) fusion reactions are studied in a pulsed plasma in the glow discharge regime using a benchtop apparatus. We model plasma conditions using particle-in-cell codes. Advantages of this approach are relatively high peak ion currents and current densities (0.1 to several A/cm^2) that can be applied to metal wire cathodes for several days. We detect neutrons from D-D reactions with scintillator-based detectors. For palladium targets, we find neutron yields as a function of cathode voltage that are over 100 times higher than yields expected for bare nuclei fusion at ion energies below 2 keV (center of mass frame). A possible explanation is a correction to the ion energy due to an electron screening potential of 1000+/-250 eV, which increases the probability for tunneling through the repulsive Coulomb barrier. Our compact, robust setup enables parametric studies of this effect at relatively low reaction energies.
Discharge structure refers to the morphology of different plasma quantities, such as electron temperature, reaction rate, plasma potential, mass flux, net charge and species density, which are determined by plasma transport mechanism and chemical processes. This morphology is rather difficult to refine in complex electronegative plasma for it is contained in a multiple-physics-field coupled system. Regarding this difficulty, the combination of self-consistent simulation, theory analysis and experimental diagnostic of this system is needed. In the scope of present article, the fluid simulation …
The nonperturbing experimental methods have been described, by means of which the solitary vortex structures in gas-discharge nonneutral electron plasma were detected and investigated. The comparison with the experimental methods used in devices with pure electron plasma was made. The problems of shielding the electrostatic perturbations in nonneutral plasmas were considered.
Dusty plasma crystals have traditionally been observed and studied in radio frequency (RF) discharge plasmas and their formation in a DC glow discharge plasma remains experimentally challenging. We report the first ever observation of a stable dusty plasma Coulomb crystal in the cathode sheath region of a DC glow discharge plasma. The observations are made in the DPEx device where crystals of mono-disperse Melamine Formaldehyde grains are produced in the background of an Argon plasma. The crystalline nature of the structure is confirmed through a host of measurements that includes the radial p…
The plasma-liquid interaction is an important issue in plasma technology. The simulation of discharge in spherical bubbles in the water that produced plasma-activated water (PAW) is investigated using finite element methods (FEM) for a simulated 2D dielectric barrier discharge in three different geometries. The electron density changes with voltage, frequency, dielectric thickness, and bubble radius are investigated in different time duration. The results show that electron density increases linearly by increasing voltage, frequency and bubble radius, while it is vice versa for dielectric thic…
A method of creating plasma channels with controllable depth and transverse profile for the guiding of short, high power laser pulses for efficient electron acceleration is proposed. The plasma channel produced by the hydrogen-filled capillary discharge waveguide is modified by a ns-scale laser pulse, which heats the electrons near the capillary axis. This interaction creates a deeper plasma channel within the capillary discharge that evolves on a ns-time scale, allowing laser beams with smaller spot sizes than would otherwise be possible in the unmodified capillary discharge.
Scaling or smiliarity laws of plasmas are of interest if lab size plasma sources are to be scaled for industrial processes. Ideally, the discharge parameters of the scaled plasmas are predictable and the fundamental physical processes are unaltered. Naturally, there are limitations and ranges of validity. Scaling laws for direct current glow discharges are well known. If a well diagnosed discharge is scaled, the field strength in the positive column, the gas amplification and the normal current density can easily be estimated. For non-stationary high power discharges like high power impulse ma…
The reactivity of water vapor introduced in the flowing post-discharge of an RF atmospheric plasma torch is investigated through electrical characterization, optical emission spectroscopy and mass spectrometry measurements. Due to the technical features of the plasma torch, the post-discharge can be considered as divided into two regions: an inner region (inside the plasma torch device) where the water vapor is injected and an outer region which directly interacts with the ambient air. The main reactions induced by the injection of water vapor are identified as well as those indicative of the …
Parameters of a dense 10^13-10^14cm^-3) multicomponent gas-metal plasma in the pulsed reflex discharge with a moderate power (W \leq 10 MW) have been studied. The dynamics of the plasma density in time, the mass-element composition of the plasma generated, the radial distribution of the electron density in plasma, the rotation velocity and the rotation frequency of a plasma layer with n_p \geq n_crit, the radial electric field strength, and the recombination factor at the stage of plasma density decay in the discharge have been determined. The plasma particle separation factor has been evaluat…
The analysis of experimental investigations of equilibrium, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas during the time much more than the electron-neutral collision time has been carried out. The problem of long confinement of the column of pure electron plasma in Penning-Malmberg trap is considered. The mechanism of stability of long-lived vortex structure in gas-discharge nonneutral electron plasma is investigated. The collapse of electron sheath in gas-discharge nonneutral electron plasma in Penning cell at high pressures of …
Results of experimental investigation of the ECR discharge in a single coil magnetic field as an alternative to RF and helicon discharges for wide-aperture dense plasma fluxes production are presented. A possibility of obtaining wide-aperture high density hydrogen plasma fluxes with homogenous transverse distribution was demonstrated in such a system. The prospects of using this system for obtaining high current ion beams are discussed.
Water window emission spectra of two laboratory nitrogen plasma sources were examined with a free standing grating spectrometer (FSGS). The highest line intensities at the wavelength 2.88 nm achievable with the sources were compared. Pulse energies for this line were judged as 0.02 mJ/srad and 0.16 mJ/srad with laser produced plasma system and pinching discharge plasma, respectively. The spectral resolution was found about 0.01 nm at 3rd order of spectral lines around wavelength 2.5 nm.
The results of experimental investigations of inhomogeneities of gas-discharge nonneutral electron plasma obtained by using the nonperturbing experimental methods [N.A. Kervalishvili, arXiv:1502.02516 [physics.plasm-ph] (2015)] have been presented. Inhomogeneities are the dense solitary vortex structures stretched along the magnetic field, the lifetime of which is much greater than the time of electron-neutral collisions. The processes of formation, evolution and dynamics of vortex structures were studied. The periodic sequence of these processes is described for different geometries of discha…
The formation of self-consistent dust crystal and its melting is a well known phenomenon in rf generated plasma but remains challenging in DC glow discharge plasma. Here, we report the melting of a two dimensional dusty plasma crystal, suspended in the cathode sheath of a DC glow discharge plasma. The experiments are carried out in a $Π-$shaped Dusty Plasma Experimental (DPEx) device where a stationary crystal of melamine formaldehyde particles is formed between the confining strips in a background of Argon plasma. The stable structure breaks and leads to a fluid state on reducing the neutral …
The post-discharge of an RF plasma torch supplied with helium and oxygen gases is characterized by mass spectrometry, optical emission spectroscopy and electrical measurements. We have proved the existence of a dc current in the post-discharge (1--20 A), attributed to the Penning ionization of atmospheric nitrogen and oxygenated species. The mechanisms ruling this dc current are investigated through experiments in which we discuss the influence of the O2 flow rate, the He flow rate and the distance separating the plasma torch from a material surface located downstream.
The formation of electron groups is a common phenomenon in gas discharges and space plasmas. We describe similarities between electron kinetics in solar wind, cathode region of glow discharges, and magnetic nozzles. Remarkable resemblances between adiabatic focusing of magnetized electrons and spherical geometry effects for neutral particles escaping planet atmosphere are pointed out. The previously developed kinetic solvers for electrons coupled to Poisson equation for self-consistent simulations of the electric field are used to analyse the formation of electron groups in the cathode region …
The self-excitation of plasma series resonance (PSR) oscillations is a prominent feature in the current of low pressure capacitive radio frequency (RF) discharges. This resonance leads to high frequency oscillations of the charge in the sheaths and enhances electron heating. Up to now, the phenomenon has only been observed in asymmetric discharges. There, the nonlinearity in the voltage balance, which is necessary for the self-excitation of resonance oscillations with frequencies above the applied frequencies, is caused predominantly by the quadratic contribution to the charge-voltage relation…
In this work we report recent results of our experimental and theoretical studies related to plasma conversion of liquid ethanol into hydrogen-enriched syngas in the plasma-liquid system with the electric discharge in a gas channel with liquid wall using available diagnostics and numerical modeling.
The plasma parameters such as electron distribution function and electron density of three atmospheric-pressure transient discharges namely filamentary and homogeneous dielectric barrier discharges in air, and the spark discharge of argon plasma coagulation (APC) system are determined. A combination of numerical simulation as well as diagnostic methods including current measurement and optical emission spectroscopy (OES) based on nitrogen emissions is used. The applied methods supplement each other and resolve problems, which arise when these methods are used individually. Nitrogen is used as …
The results of experimental investigations of the ejection of electrons from gas-discharge nonneutral electron plasma at interaction of vortex structures have been given. The periodical approach of vortex structures causes the ejection of electrons both from the vortex structures themselves and from the adjacent regions of electron sheath to the end cathodes of discharge device. The ejection takes place in the form of short and long pulses following each other. The nature of these pulses and the dynamics of interaction of vortex structures at their approach were studied.
Photoelectron emission measurements have been performed using a filament-driven multi-cusp arc discharge volume production H^- ion source (LIISA). It has been found that photoelectron currents obtained with Al, Cu, Mo, Ta and stainless steel (SAE 304) are on the same order of magnitude. The photoelectron currents depend linearly on the discharge power. It is shown experimentally that photoelectron emission is significant only in the short wavelength range of hydrogen spectrum due to the energy dependence of the quantum efficiency. It is estimated from the measured data that the maximum photoel…
The model of gas-discharge nonneutral electron plasma has been considered, in which the electron density is limited by non-linear processes initiated by diocotron instability and it does not depend on the mechanism of electron transport across the magnetic field. The model describes well the characteristics of electron sheath and the current characteristics of discharge both, in magnetron geometry and in the geometry of inversed magnetron, and it allows us to describe quantitatively the influence of anode misalignment on the discharge electron sheath for the first time. The scope of applicabil…
The detail structure of energy output and the dynamic characteristics of electric spark discharge process have been studied to calculate the energy of electric spark induced plasma under different discharge condition accurately. A series of electric spark discharge experiments were conducted with the capacitor stored energy in the range of 10J 100J and 1000J respectively. And the resistance of wire, switch and plasma between electrodes were evaluated by different methods. An optimized method for electric resistance evaluation of the full discharge circuit, three poles switch and electric spark…
The results of experimental investigations of electron ejection from gas-discharge nonneutral electron plasma at the formation and radial oscillations of vortex structure have been presented. The electrons are injected from the vortex structure and the adjacent region of electron sheath in the form of pulses the duration and periodicity of which are determined by the processes of evolution and dynamics of this structure. The possible mechanisms of pulse ejection of electrons are considered. The influence of electron ejection on other processes in discharge electron sheath is analyzed.
It is shown that under the definite regime of interaction of the acoustic waves with low-temperature, partially ionized plasma it is possible to change the intensity of some spectral lines of atomic argon. It is shown also, that the dependence of the intensities of these spectral lines on the intensity of the acoustic wave has a hysteresis behavior.
The comparative analysis of the results of experimental investigations of the processes of formation, interaction and dynamics of vortex structures in pure electron and gas-discharge electron nonneutral plasmas taking place for the period of time much less than the electron-neutral collision time has been given. The general processes of formation and behavior of vortex structures in these two plasmas were considered. The phenomena, taking place only in one of these plasmas were also considered. It is shown that the existing difference in behavior of vortex structures is caused by different ini…
In the paper, the functional definition of a plasma for-injector of separable material is presented, and the requirements to it are formulated. The version of a device for the material separation into elements based on the beam-plasma discharge is under consideration. The dimensions of a pilot separating device are determined. The following quantities are estimated: the particle concentration per unit length of the separating device, effective length of the beam-plasma interaction (BPI) within the separating device, dynamics of a plasma density increase for metallic uranium, and thermal charac…
A technique to generate jets of pure Titanium plasma is presented. A Ti wire is exploded in an Alumina capillary sealed with 1atm. of air inside. The generated plasma emerges from the capillary (to a high-vacuum environment) by ripping a thin Ti foil that seals one of the capillary ends. The generated plasma jets have a velocity of up to $4.5\pm0.5mm/μs$, an electron temperature of $1.5\pm0.5eV$ and a ion density of $2.7\pm1\times10^{17}/cc$. The plasma source was designed for a capillary discharge extreme ultraviolet laser experiment, but might also be useful to other application such as a ta…
The discharge structure of inductively coupled plasma is studied via fluid simulation and analytic theory collaboration. At low pressure, the discharge is stratified by the double layer, which is modelled as dipole moment. The parabolic profile is formed in the discharge core when recombination loss is negligible and both the electron and anions are the Boltzmann balanced. At increasing the pressure, the main characteristics, i.e., parabolic, elliptic and flat-topped profile, are experienced, predicted by the simulation and analytics. Self-coagulation is accompanied at all considered pressures…
Plasma kinetics of molecular hydrogen in the electrical discharge in Ar/CH3OH/H2O mixture is theoretically investigated for the first time. It is researched the dependence of [H2] on the breakdown field, the discharge power, solution compound and the argon pumping rate through the interelectrode gap. The highest hydrogen concentration is reached with the 20% methanol fraction in the solution. It is shown that [H2] grows as the linear function of the discharge power and decreases with the gas volume velocity increase.
This paper reports on experimental work related to a technology development project that had to be abandoned in the wake of the COVID-19 pandemic. Recognizing that the window of opportunity for timely exploitation of this technology is no longer open and also taking into account the likely future commercial value of the downstream innovations, it was decided to partially release proprietary experimental information which is of current scientific interest to the plasma focus community. This information pertains to the replacement of the traditional plasma initiation method using a sliding disch…
We conducted experimental studies and computer simulations of standing striations in capacitive coupled plasma in Argon gas. Standing striations were observed at frequencies 3.6, 8.4 and 19.0 MHz, in a pressure range 0.05-10 Torr, tube radius R=1.1 cm, for a certain range of discharge currents (plasma densities). Numerical simulations revealed similar nature of standing striations in CCP and moving striations in DC discharges under similar discharge conditions. Comparison of computer simulations with experimental observations helped clarify the nature of these striations. The non-linear depend…
The electron sheath formation in a DC magnetised plasma of modified hollow cathode source is studied. The discharge consists of two plane parallel cathodes and a small cubical anode placed off axis at the center. The argon plasma is produced and the properties of the plasma in response to the sheath formation near the anode are studied using electrical and optical diagnostics. In particular, the effect of pressure, magnetic field on discharge parameters such as discharge current, plasma potential, plasma density and electron temperature is studied. The discharge showed an onset of anode glow a…
Transition from chaotic to ordered state has been observed during the initial stage of a discharge in a cylindrical dc glow discharge plasma. Initially it shows a chaotic behavior but increasing the discharge voltage changes the characteristics of the discharge glow and shows a period substraction of order 7 period $\to$ 5 period $\to$3 period $\to$1 period i.e. the system goes to single mode through odd cycle subtraction. On further increasing the discharge voltage, the system goes through period doubling, like 1 period $\to$ 2 period $\to$ 4 period. On further increasing the voltage, the sys…
A method for the asymmetric focusing of electron bunches, based on the active plasma lensing technique is proposed. This method takes advantage of the strong inhomogeneous magnetic field generated inside the capillary discharge plasma to focus the ultrarelativistic electrons. The plasma and magnetic field parameters inside the capillary discharge are described theoretically and modeled with dissipative magnetohydrodynamic computer simulations enabling analysis of the capillaries of rectangle cross-sections. Large aspect ratio rectangular capillaries might be used to transport electron beams wi…
In order to break the limitation of plasma nitriding technology,which can be applied to a few nonmetallic gaseous elements, the "Double Glow Discharge Phenomenon" was found and then invented the "Double Glow Plasma Surface Metallurgy Technology". This double glow plasma surface metallurgy technology can use any element in the periodic table of chemical elements for surface alloying of metal materials. Countless surface alloys with special physical and chemical properties have been produced on the surfaces of conductive materials.By using double glow discharge phenomenon,a series of new plasma …
The complex theoretical and experimental investigation of plasma kinetics of the electric discharge in the mixture of air and ethanol-water vapors is carried out. The discharge was burning in the cavity, formed by air jets pumping between electrodes, placed in aqueous ethanol solution. It is found out that the hydrogen yield from the discharge is maximal in the case when ethanol and water in the solution are in equal amounts. It is shown that the hydrogen production increases with the discharge power and reaches the saturation at high value. The concentrations of the main stable gas-phase comp…
The influence of charge trap states in the dielectric boundary material on capacitively coupled radio frequency plasma discharge is investigated with theory and Particle in cell/Monte Carlo Collision simulation. It is found that the trap states of the wall material manipulated discharge properties mainly through the varying ion induced secondary electron emission (SEE) coefficient in response to dynamic surface charges accumulated within solid boundary. A comprehensive SEE model considering surface charging is established first, which incorporates the valence band electron distribution, electr…
Pin-to-liquid discharges are investigated for the activation of liquids dedicated to agriculture applications. They are characterized through their electrical and optical properties, with a particular attention paid to their filaments and self-organized patterns occurring at the liquid interface. We show how modulating their interaction with ambient air can promote the production of reactive species in liquids such as H2O2, NO2- and NO3-. The effects of the resulting plasma activated media are reported on lentils seeds.
Thermophoresis is a tool often applied in complex plasma experiments. One of the usual stated benefits over other experimental tools is that changes induced by thermophoresis neither directly depend on, nor directly influence, the plasma parameters. From electronic data, plasma emission profiles in the sheath, and Langmuir probe data in the plasma bulk, we conclude that this assumption does not hold. An important effect on the levitation of dust particles in argon plasma is observed as well. The reason behind the changes in plasma parameters seems to be the change in neutral atom density accom…
An alternative explanation to the mechanism behind self-sustained oscillations of ions in direct current (DC) glow discharges is provided. Such description is distinguished from the one provided by the fluid models, where oscillations are attributed to the positive feedback mechanism associated with photoionization of particles and photoemission of electrons from the cathode. Here, oscillations arise as consequence of interaction between an ion and the surface charges induced by it at the bounding electrodes. Such mechanism provides an elegant explanation to why self-sustained oscillations occ…
The crucial role that Ions Energy Distribution Function (IEDF) at the electrodes plays in plasma processing of semiconductor materials demands that this quantity be predicted with high accuracy and with low noise levels in any plasma simulator. In this work, an efficient Particle-in-cell/Monte-Carlo (PIC/MC) simulator is developed to model IEDF at the electrodes of electronegative plasma discharges. The simulator uses an effective method to increase the number of MC particles in regions of low particle density by splitting the particles and by adjusting their statistical weight. This statistic…
Plasma properties inside a hydrogen-filled capillary discharge waveguide were modeled with dissipative magnetohydrodynamic simulations to enable analysis of capillaries of circular and square cross-sections implying that square capillaries can be used to guide circularly-symmetric laser beams. When the quasistationary stage of the discharge is reached, the plasma and temperature in the vicinity of the capillary axis has almost the same profile for both the circular and square capillaries. The effect of cross-section on the electron beam focusing properties were studied using the simulation-der…
Interaction of an intense electron beam with a finite-length, inhomogeneous plasma is investigated numerically. The plasma density profile is maximal in the middle and decays towards the plasma edges. Two regimes of the two-stream instability are observed. In one regime, the frequency of the instability is the plasma frequency at the density maximum and plasma waves are excited in the middle of the plasma. In the other regime, the frequency of the instability matches the local plasma frequency near the edges of the plasma and the intense plasma oscillations occur near plasma boundaries. The la…
The effects of nanosecond pulsed non-equilibrium plasma discharges on ignition characteristics and low-temperature chemistry or LTC of DME/O2/Ar mixtures are numerically investigated in a plane-to-plane geometry at a reduced pressure of 76 Torr. Detailed numerical investigations of the two-stage ignition process in different temperature regimes of DME have been created through a high-fidelity one-dimensional, multi-timescale plasma-discharge model. Two different initial temperatures are set for comparison: 550K, the negative temperature coefficient regime, where LTC plays a dominate role; 800K…
The results of a detailed kinetic study of the main plasma chemical processes in non-equilibrium ethanol/argon plasma are presented. It is shown that at the beginning of the discharge the molecular hydrogen is mainly generated in the reaction of ethanol H-abstraction. Later hydrogen is formed from active H, CH2OH and CH3CHOH and formaldehyde. Comparison with experimental data has shown that the used kinetic mechanism predicts well the concentrations of main species at the reactor outlet.
The use of dielectric barrier discharge (DBD) plasmas has become a practical way to carry out surface treatment and one seeks to do it in a more efficient way, which requires to have control of the plasma parameters like rotational and vibrational temperatures (T_rot and T_vib). Since the T_vib of an atmospheric pressure plasma jet is an important parameter related to improvement of surface treatments, in this work it was analyzed two methods to increase the values of T_vib in the DBD plasma. One of the methods is to reduce the exit size of the DBD reactor, and the other is to change the gas f…
An experimental investigation on the periodic and chaotic oscillations in a reflex plasma source in presence of magnetic field is presented. The experiment is conducted in a reflex plasma source, consisting of two cathodes and a ring anode. A penning type DC glow discharge in an uniform axial magnetic field is initiated in the background of argon gas. The current-voltage characteristics near the breakdown voltage show a hysteresis with two distinct discharge current regimes. The effect of magnetic field on the discharge current and floating potential oscillations is studied when the discharge …
This paper presents the results of a theoretical and experimental study of plasma-assisted reforming of ethanol into molecular hydrogen in a new modification of the "tornado" type electrical discharge. Numerical modeling clarifies the nature of the non-thermal conversion and explains the kinetic mechanism of nonequilibrium plasma-chemical transformations in the gas-liquid system and the evolution of hydrogen during the reforming as a function of discharge parameters and ethanol-to-water ratio in the mixture. We also propose a scheme of chemical reactions for plasma kinetics description. It is …
