HIDPL Articles

Permanent URI for this collectionhttps://hdl.handle.net/2104/5505

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A machine learning-based Bayesian optimization solution to nonlinear responses in dusty plasmas
(IOP PUblishing, 2021-06) Ding, Zhiyue; Matthews, Lorin; Hyde, Truell
Nonlinear frequency response analysis is a widely used method for determining system dynamics in the presence of nonlinearities. In dusty plasmas, the plasma–grain interaction (e.g. grain charging fluctuations) can be characterized by a single-particle non-linear response analysis, while grain–grain non-linear interactions can be determined by a multi-particle non-linear response analysis. Here a machine learning-based method to determine the equation of motion in the non-linear response analysis for dust particles in plasmas is presented. Searching the parameter space in a Bayesian manner allows an efficient optimization of the parameters needed to match simulated non-linear response curves to experimentally measured non-linear response curves.
Dust as probes: Determining confinement and interaction forces
(IOP Publishing, 2020-10) Hartmann, Peter; Rosenberg, Marlene; Juhasz, Z.; Matthews, Lorin; Sanford, Dustin; Vermillion, Katrina; Reyes, Jorge; Hyde, Truell
The PK-4 system is a micro-gravity dusty plasma experiment currently in operation on-board the International Space Station. The experiment utilizes a long DC discharge in neon or argon gases. We apply our 2D particle-in-cell with Monte Carlo collisions discharge simulation to compute local plasma parameters that serve as input data for future dust dynamics models. The simulation includes electrons, Ne+ ions, and Ne^m metastable atoms in neon gas and their collisions at solid surfaces including secondary electron emission and glass wall charging. On the time scale of the on-board optical imaging, the positive column appears stable and homogeneous. On the other hand, our simulations show that on microsecond time scales the positive column is highly inhomogeneous: ionization waves with phase velocities in the range between 500 m s−1 and 1200 m s−1 dominate the structure. In these waves, the electric field and charged particle densities can reach amplitudes up to 10 times of their average value. Our experiments on ground-based PK-4 replica systems fully support the numerical findings. In the experiment, the direction of the DC current can be alternated, which has been found to favor dust particle chain formation. We discuss possible mechanisms for how the highly oscillatory plasma environment contributes to the dust particle chain formation.
Ionization waves in the PK-4 direct current neon discharge
(American Physical Society, 2020-11) Ashrafi, Khandaker; Yousefi, Raziyeh; Chen, Mudi; Matthews, Lorin; Hyde, Truell
Complex plasmas are interesting systems as the charged dust can self-assemble into different types of ordered structures. To understand the mechanisms which govern the transitions from one type of structure to another, it is necessary to know both the dust charge and the confi ning electric fields within the environment, parameters which are difficult to measure independently. As dust is usually confi ned in a plasma sheath where the ions stream from the bulk plasma the negative lower electrode, the problem is further complicated by the ion wake field, which develops downstream of the dust grains in a flowing plasma. The differences in local ion density caused by the wake fi eld change the equilibrium dust charge and shielding distance of the dust grains, and thus affect the interaction between grains. Here we use a molecular dynamics simulation of ion flow past dust grains to investigate the interaction between the dust particles and ions. We consider a long vertical chain of particles confi ned within a glass box placed on the lower electrode of a GEC rf reference cell. We apply the model iteratively to self-consistently determine the dust charge, electric fi eld, and ion density along the length of the chain as well as the ion flow speed. Simulation results indicate that the ion flow speed within the box is subsonic.
Nonlinear mode coupling and internal resonance observed in a dusty plasma
(New Journal of Physics, 2009-10) Ding, Zhiyue; Qiao, Ke; Ernst, N.; Kong, Jie; Chen, M.; Matthews, L.S.; Hyde, T. W.
In this paper, we report the first experimental observation of internal resonance in a dusty plasma, which shows the intrinsic nonlinearities of dust interactions in plasmas. When driving a system of vertically aligned dust particle pairs in the vertical direction, the horizontal motion is found to be excited during onset of internal resonance when the higher-frequency horizontal sloshing mode is nonlinearly coupled to the vertical breathing mode through the 1:2 commensurable relation. A theoretical model of the nonlinear interaction of dust particles in plasma is also provided and the results of the theoretical model are shown to match experimental observations.
Dust particle pair correlation functions and the non-linear effect of interaction potentials
(IEEE Transactions on Plasma Science, 2019-07) Kong, Jie; Qiao, Ke; Matthews, L.S.; Hyde, T.W.
Dust temperature is a measure of the energy of the stochastic motion of a dust particle, and is a result of the combination of the Brownian motion and the fluctuations in the dust charge and confining electric field. A method using the equilibrium value of the mean square displacement was recently introduced to obtain the dust temperature experimentally. As a follow up, this paper investigates the relationship between the temperature derived from the mean square displacement technique and a technique using the probability distribution of the displacements obtained from random fluctuations of the dust particle. Experimental results indicate that the harmonic confinement potential acting on the dust particle can be obtained by combining the two methods, allowing the non-linear effect of the confining force to be investigated. The thermal expansion in a one-dimensional vertical chain is discussed as a representative application as it is related to the non-linear confinement force, or the asymmetric confinement potential.
Comparison of Plasma Magnetic Field Interactions in a Static and Dynamic Plasma Facility
(Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan, 2016) Dropmann, Michael; Knapp, A.; Eichhorn, C.; Loehle, S.; Laufer, Rene; Herdrich, Georg; Matthews, Lorin Swint.; Hyde, Truell Wayne.; Fasoulas, Stefanos; Roeser, Hans-Peter
Magnetic fields are a principal/widespread/promising tool/instrument in space technology design for the use in advanced propulsion concepts, shielding from radiation or to aid thermal protection during the atmospheric entry of spacecraft. Two experiments have been conducted to investigate the feasibility of using magnetic fields to reduce the heat flux onto a thermal protection system during atmospheric entry. For this purpose a modified heat flux probe with embedded permanent magnets has been exposed to a plasma jet and the structure of the bow shock in front of the probe has been observed using an emission spectroscopy setup. The intensity ratio of ionized argon lines for the experiment with and without magnets has been determined and used to analyze the magnetic field`s impact on the flow. Complementary experiments in a low power capacitively driven plasma have been conducted using micron sized particles as probes to map electric fields in a magnetically perturbed plasma. The results from both experiments are presented and analogies are drawn from both approaches. The experiments have shown that the interactions of the magnetic field with the plasma can create strong electric fields which strongly influence the ions even though the field is too weak to magnetize the ions.
Dust particle pair correlation functions and the non-linear effect of interaction potentials
(IEEE Transactions on Plasma Science, 2019-07) Kong, Jie; Qiao, Ke; Matthews, Lorin Swint.; Hyde, Truell Wayne.
Dust kinetic temperature is a measure of the energy of the stochastic motion of a dust particle and is a result of the combination of the Brownian motion and the fluctuations in the dust charge and confining electric field. A method using the equilibrium value of the mean square displacement was recently introduced to obtain the dust kinetic temperature experimentally. As a follow up, this paper investigates the relationship between the dust kinetic energy derived from the mean square displacement technique and a technique using the probability distribution of the displacements obtained from random fluctuations of the dust particle. The experimental results indicate that the harmonic confinement potential acting on the dust particle can be obtained by combining the two methods, allowing the nonlinear effect of the confining force to be investigated. The thermal expansion in a 1-D vertical chain is discussed as a representative application as it is related to the nonlinear confinement force, or the asymmetric confinement potential.
Nonlinear response of vertical paired structure in complex plasma
(Plasma Physics and Controlled Fusion, 2019-03-21) Ding, Zhiyue; Qiao, Ke; Kong, Jie; Matthews, Lorin Swint.; Hyde, Truell Wayne.
The effect of the ion wake downstream of grains immersed in a flowing plasma is observed experimentally through the apparent non-reciprocal grain–grain interactions. Here we extend amplitude-frequency response analysis to examine the nonlinear components of the interaction of a dust particle pair aligned with the ion flow. The particle pair is modeled as two forced coupled oscillators, and a new coordinate system is introduced in which the breathing and sloshing modes are linearly decoupled. Multiple-scale analysis is used to derive analytical expressions for the response in the vertical direction for each mode in this coordinate system. By fitting the analytical expressions to experimentally measured response curves, the nonlinear part of the wake-modified particle–particle interaction is determined and identified as the source for the coupling between the sloshing and breathing modes. It is found that the restoring force acting on the downstream particle is more linear, thus stabilizing the oscillations of the downstream grain.
Mapping the Plasma Potential in a Glass Box
(IEEE Transactions on Plasma Science, 2019-07) Scott, Lori; Ellis, Naoki; Chen, Mudi; Matthews, Lorin Swint.; Hyde, Truell Wayne.
Modeling the dynamics of charged dust particles, confined in a glass box placed on the lower electrode of a Gaseous Electronics Conference cell, requires that the interactions between the charged dust, plasma, and boundaries need to be accounted for in a self-consistent manner. The charged lower electrode affects the plasma conditions throughout the glass box, altering the electron and ion densities and temperatures within the plasma sheath. These plasma characteristics determine the charge collected on the walls of the surrounding glass box, the electric potential within the glass box, the dust charge, and ultimately the dynamics of the dust. This paper describes the steps taken to build a simple model of the relationship between the plasma conditions and the potential within the box as well as the expected dust charge near the center of the box. The calculated potential and dust charge are used to construct acceleration maps for the dust, which are compared to experimentally measured acceleration of the dust within the box.
Self-diffusion in two-dimensional quasi-magnetized rotating dusty plasmas
(Physical Review E, 2019-01-10) Hartmann, Peter; Reyes, J. C.; Kostadinova, Eva Georgieva, 1992-; Matthews, Lorin Swint.; Hyde, Truell Wayne.; Dzhumagulova, K. N.; Masheyeva, R. U.; Ramazanov, T. S.; Ott, T.; kahlert, H.; Bonitz, M.; Korolov, I.; Donko, Zoltan
The self-diffusion phenomenon in a two-dimensional dusty plasma at extremely strong (effective) magnetic fields is studied experimentally and by means of molecular dynamics simulations. In the experiment the high magnetic field is introduced by rotating the particle cloud and observing the particle trajectories in a corotating frame, which allows reaching effective magnetic fields up to 3000 T. The experimental results confirm the predictions of the simulations: (i) superdiffusive behavior is found at intermediate timescales and (ii) the dependence of the self-diffusion coefficient on the magnetic field is well reproduced.
Simple experiment on the sputtering rate of solids in gas discharges
(Physics of Plasmas, 2017-06) Hartmann, Peter; Carmona-Reyes, Jorge; Korolov, I.; Matthews, Lorin S.; Hyde, Truell W.
We present a very simple and sensitive method to measure the sputtering rate of solid materials in stationary low-pressure gas discharges. The method is based on the balance of the centrifugal force and the confinement electric force acting on a single electrically charged dust particle in a rotating environment. We demonstrate the use and sensitivity of this method in a capacitively coupled radio frequency argon discharge. We were able to detect a reduction of 10 nm in the diameter of a single dust particle.
Using Dust as Probes to Determine Sheath Extent and Structure
(Journal of Plasma Physics, 2016-07) Douglass, Angela Michelle.; Land, Victor; Matthews, Lorin; Hyde, Truell W.
Two in situ experimental methods are presented in which dust particles are used to determine the extent of the sheath and gain information about the time-averaged electric force profile within a radio frequency (RF) plasma sheath. These methods are advantageous because they are not only simple and quick to carry out, but they also can be performed using standard dusty plasma experimental equipment. In the first method, dust particles are tracked as they fall through the plasma towards the lower electrode. These trajectories are then used to determine the electric force on the particle as a function of height as well as the extent of the sheath. In the second method, dust particle levitation height is measured across a wide range of RF voltages. Similarities were observed between the two experiments, but in order to understand the underlying physics behind these observations, the same conditions were replicated using a self-consistent fluid model. Through comparison of the fluid model and experimental results, it is shown that the particles exhibiting a levitation height that is independent of RF voltage indicate the sheath edge – the boundary between the quasineutral bulk plasma and the sheath. Therefore, both of these simple and inexpensive, yet effective, methods can be applied across a wide range of experimental parameters in any ground-based RF plasma chamber to gain useful information regarding the sheath, which is needed for interpretation of dusty plasma experiments.
Temperature Measurements of a Dust Particle
(Journal of Plasma Physics, 2016-09) Kong, Jie; Qiao, Ke; Matthews, Lorin; Hyde, Truell W.
The thermal motion of a dust particle levitated in a plasma chamber is similar to that described by Brownian motion in many ways. The primary difference between a dust particle in a plasma system and a free Brownian particle is that in addition to the random collisions between the dust particle and the neutral gas atoms, there are electric field fluctuations, dust charge fluctuations, and correlated motions from the unwanted continuous signals originating within the plasma system itself. This last contribution does not include random motion and is therefore separable from the random motion in a ‘normal’ temperature measurement. In this paper, we discuss how to separate random and coherent motions of a dust particle confined in a glass box in a Gaseous Electronic Conference (GEC) radio-frequency (RF) reference cell employing experimentally determined dust particle fluctuation data analysed using the mean square displacement technique.
Ion-wake Field inside a Glass Box
(Physical Review E, 2016-09) Chen, Mudi; Dropmann, Michael; Matthews, Lorin; Hyde, Truell W.
The confinement provided by a glass box is proving ideal for the formation of vertically aligned structures and a convenient method for controlling the number of dust particles comprising these dust structures as well as their sizes and shapes. In this paper, the electronic confinement of the glass box is mapped, and the particle interactions between the particle pairs inside the glass box are measured. The ion-wake field is shown to exist within the glass box, and its vertical and horizontal extents are measured.
Mapping of force field in a capacitively driven rf plasma discharge
(Journal of Plasma Physics, 2016-07) Dropmann, Michael; Chen, Mudi; Sabo, Hannah; Laufer, Rene; Herdrich, Georg; Matthews, Lorin; Hyde, Truell W.
In this paper a method is described that allows mapping of the forces acting on dust particles in a GEC reference cell. Monodisperse particles are dropped into the plasma environment and their trajectories are tracked using a high-speed camera system to determine local accelerations and respective forces. Collecting data from a large number of particle drops allows the identification of three-dimensional vector fields for the acting forces. The procedure is described and multiple examples in which the method has been applied are given. These examples include a simple plasma sheath, plasmas perturbed by a horizontal and vertical dipole magnet, an array of multiple magnets mimicking the fields found at a lunar swirl, and the fields inside a glass box used for particle confinement. Further applicability in other plasma environments will be discussed shortly.
Analysis of Magnetic Field Plasma Interactions Using Micro Particles as Probes
(American Physics Society/ Physical Review E, 2015-08-26) Dropmann, Michael; Laufer, Rene; Herdrich, Georg; Matthews, Lorin Swint; Hyde, T. W.
The interaction between a magnetic field and plasma close to a nonconductive surface is of interest for both science and technology. In space, crustal magnetic fields on celestial bodies without atmosphere can interact with the solar wind. In advanced technologies such as those used in fusion or spaceflight, magnetic fields can be used to either control a plasma or protect surfaces exposed to the high heat loads produced by plasma. In this paper, a method will be discussed for investigating magnetic field plasma interactions close to a nonconductive surface inside a Gaseous Electronics Conference reference cell employing dust particles as probes. To accomplish this, a magnet covered by a glass plate was exposed to a low power argon plasma. The magnetic field was strong enough to magnetize the electrons, while not directly impacting the dynamics of the ions or the dust particles used for diagnostics. In order to investigate the interaction of the plasma with the magnetic field and the nonconductive surface, micron-sized dust particles were introduced into the plasma and their trajectories were recorded with a high-speed camera. Based on the resulting particle trajectories, the accelerations of the dust particles were determined and acceleration maps over the field of view were generated which are representative of the forces acting on the particles. The results show that the magnetic field is responsible for the development of strong electric fields in the plasma, in both horizontal and vertical directions, leading to complex motion of the dust particles.
Dusty plasma cavities: Probe-induced and natural
(American Physical Society, 2015-06-22) Harris, Brandon Joseph.; Matthews, Lorin Swint.; Hyde, Truell Wayne.
A comprehensive exploration of regional dust evacuation in complex plasma crystals is presented.Voids created in three-dimensional crystals on the International Space Station have provided a rich foundation for experiments, but cavities in dust crystals formed in ground-based experiments have not received as much attention. Inside a modified Gaseous Electronics Conference rf cell, a powered vertical probe was used to clear the central area of a dust crystal, producing a cavity with high cylindrical symmetry. Cavities generated by three mechanisms are examined. First, repulsion of micrometer-sized particles by a negatively charged probe is investigated. A model of this effect developed for a dc plasma is modified and applied to explain experimental data in rf plasma. Second, the formation of natural cavities is surveyed; a radial ion drag proposed to occur due to a curved sheath is considered in conjunction with thermophoresis and a flattened confinement potential above the center of the electrode. Finally, cavity formation upon increasing the probe potential above the plasma floating potential is justified by a combination of ion drag and sheath edge modification. The cavities produced by these methods appear similar, but each is shown to be facilitated by fundamentally different processes.
Electrical Conductivity of the Thermal Dusty Plasma under the Conditions of a Hybrid Plasma Environment Simulation Facility
(New Journal of Physcis, 2015-05-27) Zhukhovitskii, D.; Petrov, O.; Hyde, Truell Wayne.; Herdrich, Georg; Laufer, Rene; Dropmann, Michael; Matthews, Lorin Swint.
We discuss the inductively heated plasma generator (IPG) facility in application to the generation of the thermal dusty plasma formed by the positively charged dust particles and the electrons emitted by them. We develop a theoretical model for the calculation of plasma electrical conductivity under typical conditions of the IPG. We show that the electrical conductivity of dusty plasma is defined by collisions with the neutral gas molecules and by the electron number density. The latter is calculated in the approximations of an ideal and strongly coupled particle system and in the regime of weak and strong screening of the particle charge. The maximum attainable electron number density and corresponding maximum plasma electrical conductivity prove to be independent of the particle emissivity. Analysis of available experiments is performed, in particular, of our recent experiment with plasma formed by the combustion products of a propane–air mixture and the CeO2 particles injected into it. A good correlation between the theory and experimental data points to the adequacy of our approach. Our main conclusion is that a level of the electrical conductivity due to the thermal ionization of the dust particles is sufficiently high to compete with that of the potassium-doped plasmas.
Mode couplings and resonance instabilities in finite dust chains
(American Physical Society, 2015-05-08) Qiao, Ke; Kong, Jie; Matthews, Lorin Swint.; Hyde, Truell Wayne.
Employing a numerical simulation, the normal modes are investigated for finite, one-dimensional horizontal dust chains in complex plasma. Mode couplings induced by the ion flow within the sheath are identified in the mode spectra and the coupling rules are determined. Two types of resonance-induced instabilities are observed, one bidirectional and one unidirectional. Bidirectional instability is found to cause melting of the chain with the melting proceeding via a two-step process which obeys the Lindemann criterion. The relationship between the normal mode spectra observed in finite systems and the wave dispersion relations seen in larger systems was also examined using a dust chain model. For this case, the dispersion relation was obtained through multiplication of the mode spectra matrix by a transition matrix. The resulting dispersion relations exhibit both the general features observed in larger crystals as well as several characteristics unique to finite systems, such as discontinuities and strong energy-density fluctuations.
Mode coupling and resonance instabilities in quasi-two-dimensional dust clusters in complex plasmas
(American Physical Society, 2014-09-16) Qiao, Ke; Kong, Jie; Carmona-Reyes, Jorge; Matthews, Lorin Swint.; Hyde, Truell Wayne.
Small quasi-two-dimensional dust clusters consisting of three to eleven particles are formed in an argon plasma under varying rf power. Their normal modes are investigated through their mode spectra obtained from tracking the particles’ thermal motion. Detailed coupling patterns between their horizontal and vertical modes are detected for particle numbers up to 7 and discrete instabilities are found for dust clusters with particle number 9, as predicted in previous theory on ion-flow induced mode coupling in small clusters. The instabilities are proven to be induced by resonance between coupled horizontal and vertical normal modes.

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