Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session GO06: Fundamental: Strongly Coupled, Dusty, and Interfacial PlasmasOn Demand
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Chair: Saikat Chakraborty Thakur, Auburn University Room: Rooms 310-311 |
Tuesday, November 9, 2021 9:30AM - 9:42AM |
GO06.00001: Sarkas: A Fast Pure-Python Molecular Dynamics Suite for Non-Ideal Plasmas Luciano G Silvestri, Lucas J Stanek, Gautham Dharuman, Yongjun Choi, Michael S Murillo Molecular Dynamics (MD) is a powerful tool for simulating complex dynamical systems. MD plays a central role in a diverse set of plasma subfields concerned with understanding mi-croscopic particles such as non-ideal dense plasmas. Historically, computational plasma physicists have developed their own codes; more recently, plasma physics models are being implemented in codes originally developed for other purposes. Such strategies require the plasma physicist to be part of the development process or have the skills and time to modify existing codes. Moreover, plasma physics observables are typically not available as post-processing packages. |
Tuesday, November 9, 2021 9:42AM - 9:54AM |
GO06.00002: Application of N-body gravitational algorithm to collective charged particle dynamics Yasutaro Nishimura Conventionally, N-body simulation employs softening parameters to smooth out the singularity of the central force. In this work, the Kepler problem is solved analytically when the distance between two charged particles becomes at an order of Landau length. On top of evaluating charged particle diffusion in the presence of background magnetic field (D. Bohm, The characteristics of electrical discharges in magnetic fields, McGraw-Hill, p.65, 1949), the study is extended to investigate collective motion of plasmas. Having alike charges in the system and Debye shielding, plasma N-body simulation is expected to be less laborious in constructing hierarchies (J. Barnes and P. Hut, Nature 324, 446, 1986). |
Tuesday, November 9, 2021 9:54AM - 10:06AM |
GO06.00003: Rayleigh-Benard Convection in 2D Yukawa Liquids Under An Extreme Temperature Gradient And External Forcing : A Molecular Dynamics Study Pawandeep Kaur, Rajaraman Ganesh Rayleigh-Benard(RB) convection is a widely studied non-equilibrium system, where a fluid confined between horizontal plates shows the formation of RB convection cells(RBCC) when subjected to an external temperarure gradient, ∇T and gravity, g. Formation of such RBCC has recently been observed in strongly coupled Yukawa liquids using 2D molecular dynamics(MD) simulations. Further, the RB system in Yukawa liquids has also been used to perform several interesting numerical experiments such as verification of ECM fluctuation theorem1, generation of parallel flows from RBCC under particle-level velocity perturbations2 and effect of particle mass inhomogeneity on the stability of RBCC3. |
Tuesday, November 9, 2021 10:06AM - 10:18AM |
GO06.00004: Ultracold neutral plasma expansion in a strong uniform magnetic field Robert T Sprenkle, Scott D Bergeson We report spatial density measurements of an expanding ultracold neutral Ca+ plasma in a strong uniform magnetic field. The magnetic field strength ranges from 0 to 0.12 T, corresponding to an electron magnetization parameter ranging from β = ωc / ωp = 0 to 7. Similar to a theoretical prediction for electron kinetics [Tiwari and Baalrud, Physics of Plasmas 25, 013511 (2018)], we observe a reduction in the ion disorder-induced heating temperature by a factor of 2. The magnetic field also reduces the plasma expansion transverse to the field direction. An earlier ultracold neutral plasma experiment [Zhang et al, Physical Review Letters 100, 235002 (2008)] observed ambipolar diffusion across the field lines with a transverse expansion velocity that scaled as B-1/2. In contrast to this observation, the transverse expansion velocity in our experiments depends exponentially on the magnetic field strength. The transverse expansion falls to zero when the Larmor radius is smaller than the average interparticle spacing. The plasma expansion along the magnetic field lines appears to be self-similar, as it is for unmagnetized plasmas. We see some evidence that increasing magnetic field strength leads to increased electron temperature. |
Tuesday, November 9, 2021 10:18AM - 10:30AM |
GO06.00005: Dusty Plasma Physics on the Surface of the Moon Truell W Hyde, Masatoshi Hirabayashi, Uwe Konopka, Lorin S Matthews, Hubertus Thomas The lunar surface consists primarily of dust particles in the micron to nanometer size range. When these particles are exposed to physical forces, their behavior can become quite complex. For example, electrodynamic forces have been shown to ‘loft’ dust particles from the lunar surface. This is thought to explain the ‘lunar horizon glow’ observed in images taken by Surveyor 5, 6 and 7 (1, 2, 3). Dust particles can act as ‘active probes’ providing information about the surrounding lunar environment opening the opportunity to conduct dusty plasma experiments on the lunar surface which examine fundamental physics questions. This provides a strong impetus for the development of an instrument capable of conducting such fundamental physics experiments. The data produced by such an instrument might well answer science questions currently lacking appropriate data, for example the manner in which non-Hamiltonian forces can arise in quasi-bilayer crystals on Earth. This presentation will introduce a proposed experimental platform designed to provide this data within the boundary conditions present on the lunar surface. |
Tuesday, November 9, 2021 10:30AM - 10:42AM |
GO06.00006: Experimental Investigation of Chondrule Fine-Grained Rim Formation Graeson Griffin, Calvin Carmichael, Parker J Adamson, Jorge Martinez Ortiz, Abbie Terrell, Sara A Rothrock, Almond Sugumalwang, Alyssa Binzley, Jorge Carmona Reyes, Kenneth Ulibarri, Lorin S Matthews, Truell W Hyde There are numerous theories that attempt to explain the processes at play during the formation of a solar system. The majority of these are driven by data collected from meteorites. Inside these time capsules, one can find a snapshot of the conditions present during the protoplanetary disk phase. Interestingly, 80% of these meteorites are composed of centimeter-sized, crystalized pebbles known as chondrules. Surrounding these pebbles are “Fine-Grained Rims” (FGR’s) that in general include different features than does the surrounding matrix. FGR’s are as plentiful as the chondrules themselves and although there is no shortage of theoretical and modeling work on the subject, experimental work is sparse. This talk will cover recent experiments developed at Baylor’s Center for Astrophysics, Space Physics and Engineering Research for simulating the formation of FGR’s over time and a comparison of initial findings to previous numerical modeling results. |
Tuesday, November 9, 2021 10:42AM - 10:54AM |
GO06.00007: Positive charging of dust grains in an afterglow plasma Neeraj Chaubey, John Goree, Steven Lanham, Mark J Kushner In a glow-discharge plasma, a dust grain normally has a negative charge, but it can reverse and become positive in an afterglow. We find that this positive charge, which develops in the first few milliseconds of the afterglow, is enhanced by a dc electric field. An experiment was performed with dust grains that were electrically levitated until abruptly switching off the power that sustained the plasma, causing them to fall. Acceleration measurements yielded the residual charge of grains. The value of the positive charge, which was thousands of elementary charges, increased with the dc electric field. This trend is explained by the grains collecting ions that drift at a mobility-limited velocity, after electrons have vanished. A greater electric field drives ions to a greater kinetic energy, so that they charge grains to a larger positive potential. |
Tuesday, November 9, 2021 10:54AM - 11:06AM |
GO06.00008: How to measure charges in binary dusty plasmas Dietmar Block, Frank Wieben, Micheal Himpel, Lasse Bruhn, Andre Melzer The particle charge determines the interaction in a dusty plasma. Thus, it is of fundamental importance. However, to measure particle charges turns out to be a sophisticated task. In binary systems where the two particle species have different charges and where the charge ratio is an important parameter to describe the system a reliable charge measurement is even more challenging. This contribution reports on two methods, a configurational temperature approach and measured wave disperisons, to resolve this problem. It is shown how these methods can yield the charge ratio as well as the absolute charges of the individual particle species. |
Tuesday, November 9, 2021 11:06AM - 11:18AM |
GO06.00009: Charge measurement of silica nanoparticles in an RF-plasma by IR absorption Andre Melzer, Harald Krüger, Holger Fehske, Franz X Bronold The particle charge is an essential parameter in dusty plasmas. To measure the dust charge on submicron particles, we have performed measurements of the IR absorption of SiO2 nanoparticles confined in an argon radio-frequency plasma discharge using an FTIR spectrometer. By varying the gas pressure of the discharge and duty cycle of the applied radio-frequency voltage we observed a shift of the absorption peak of SiO2. We attribute this shift to charge-dependent absorption features of SiO2. The charge-dependent shift has been calculated for SiO2 particles and from comparisons with the experiment the particle charge has been retrieved. With the two different approaches of changing the gas pressure and altering the duty cycle we are able to deduce a relative change of the particle charge with pressure variations and an absolute estimation of the charge with the duty cycle. |
Tuesday, November 9, 2021 11:18AM - 11:30AM |
GO06.00010: Transition of a 2-D crystal to a non-equilibrium two-phase coexistence state in a dusty plasma Swarnima Singh, Krishan Kumar, M.G. Hariprasad, A. Saravanan, P. Bandyopadhyay, Abhijit Sen The transition of a 2D monolayer dust crystal to a nonequilibrium solid-liquid phase coexistence is investigated in a glow discharge Argon plasma. Initially, a monolayer crystal of MF particles is formed at a discharge voltage of 400 V and neutral gas pressure of 6 Pa. which gets converted to a two-phase coexistence state of a molten liquid at the center surrounded by a crystalline periphery when the gas pressure is reduced below a threshold value. Prior to this transition, the particles exhibit a self-excited horizontal oscillation of frequency ~30 Hz at the center of the monolayer. When the pressure is reduced further below another threshold value, the system shows a multilayer cold liquid-like behavior. Various structural and thermodynamic quantities are seen to differ significantly after a phase transition. The average kinetic energy of the central region increases and the inter-particle distance in both the coexistence phases increases with the decrease in gas pressure. Similar behaviour is seen when the discharge voltage is reduced gradually below a threshold value at a given pressure. The formation of an ion wake resulting in a Schweigert instability may be responsible for the formation of phase coexistence. |
Tuesday, November 9, 2021 11:30AM - 11:42AM |
GO06.00011: Reflection of a dust acoustic solitary wave in a weakly coupled dusty plasma Krishan Kumar, Swarnima Singh, G. Arora, P. Bandyopadhyay, Abhijit Sen An experimental investigation of the reflection of a dust acoustic solitary wave from a potential barrier in a weakly coupled dusty plasma has been carried out in an inverted pi-shaped Dusty Plasma Experimental (DPEx) device in a DC glow discharge plasma environment. The dust acoustic solitary wave is excited by modulating the plasma with a short negative Gaussian pulse that is superimposed over the discharge voltage. The solitary wave structure is seen to move towards the potential barrier, created by the sheath around a biased wire, and turn back after reflecting off the barrier. The amplitude, width, and velocity of the soliton are recorded as a function of time. The experiment is repeated for different strengths of the potential barrier and different initial amplitudes of the solitary wave. It is found that the distance of the closest approach of the solitary wave increases with the increase of the strength of the potential barrier and with the decrease of the initial wave amplitude. An emissive probe is used to measure the sheath potential and its thickness by measuring the plasma potential profile in the axial direction over a range of resistances connected to the biased wire. Our experimental observations are found to be consistent with fluid theories for the reflection of a dust acoustic solitary wave in a complex plasma. |
Tuesday, November 9, 2021 11:42AM - 11:54AM |
GO06.00012: Hyperuniformity Parameter Measurements for a 2D Strongly Coupled Dusty Plasma Vitaliy Zhuravlyov, John Goree, Jack F Douglas, Paolo Elvati, Angela Violi, Jorge A Berumen Density fluctuations can be found in all kinds of plasmas, even under equilibrium conditions. As an approach for characterizing density fluctuations, we introduce the hyperuniformity parameter $H$. A particularly interesting possibility occurs if long-wavelength density fluctuations are greatly suppressed, as indicated by a small value of $H$. We obtain the value of $H$ from the static structure factor $S(k)$ for a strongly coupled dusty plasma. We analyze $S(k)$ data from several 2D dusty plasma experiments, in which particle positions were recorded under liquid-like conditions that were sustained by laser heating. Preliminary results of our analysis show a trend where $H$ diminishes as the temperature is decreased closer to the melting point. These experimental results are compared to results of a molecular dynamics simulation. |
Tuesday, November 9, 2021 11:54AM - 12:06PM |
GO06.00013: Simulations of ion heating in the presheath due to ion-acoustic instabilities Lucas P Beving, Matthew Hopkins, Scott D Baalrud We find that ion-acoustic instabilities result in significant ion heating near the sheath edge. The heating extends into the presheath since some of the wave power reflects from the sheath. Particle-in-cell simulations were designed to test whether the instability was the source of heating by varying the source electron temperature across the threshold for exciting the ion-acoustic instability. The simulations confirm the instabilities cause heating and demonstrate that the electron-to-ion temperature ratio is locked to the threshold for instability in the unstable region near the sheath edge. The instability heating effect is significant at low pressures, but is eliminated at higher pressures where the instability is damped by ion-neutral collisions. This effect is distinct from the well understood ion heating caused by inelastic collisions with neutrals. Low temperature plasma systems that utilize a presheath for ion acceleration, such as etching and ion beam sources, could experience unwanted and significant ion heating due to this effect. |
Tuesday, November 9, 2021 12:06PM - 12:18PM |
GO06.00014: Tunnel ionization within a one-dimensional, undriven plasma sheath Taylor H Hall, Russell Hooper, Nishant Patel, Jose Pacheco Tunnel ionization of atoms can occur in the presence of strong electric fields, on the order of tens of volts per nanometer, when electrons bound to a neutral atom can tunnel through the potential barrier, resulting in an electron-ion pair. Electric fields of this magnitude are often found in the sheaths of high density, high temperature plasmas of inertial confinement fusion plasmas, or in devices such as field emitter arrays. A simple model of the tunnel ionization process for hydrogen atoms was recently added to Aleph, which is a Particle-in-cell (PIC) Direct Simulation Monte Carlo (DSMC) code developed at Sandia National Labs, thereby expanding its suite of particle-particle and particle-surface interactions to include particle-field interactions. This new functionality has been found to perform well over a large range of electric fields. A tunnel ionization reaction process was applied to a one-dimensional, undriven plasma for which results of the plasma density, plasma potential, and electric fields within the sheath will be presented. Additional simulations which include the effects of warm ions and neutrals, electron-neutral collisions and impact ionization, and the injection of neutral particles were also performed. These simulations show that the addition of electron impact ionization, combined with the injection of additional neutral hydrogen, leads to prolonged sustainment of tunnel ionization reactions in the plasma sheath. |
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