Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session TI02: Fundamental/Low Temperature PlasmasLive Streamed
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Chair: Zhehui Wang, LANL Room: Ballroom 100 B |
Thursday, October 20, 2022 9:30AM - 10:00AM |
TI02.00001: Liquid Crystal Properties of Microgravity Dusty Plasma Invited Speaker: Eva G Kostadinova In this work we demonstrate that microgravity dusty plasmas exhibit various properties of the liquid crystalline state of matter, such as alignment along common director axis, layering transitions, and pattern formation. This study combines analysis of data from the Plasmakristall-4 (PK-4) facility on board the International Space Station (ISS) with predictions from many-body simulations and analytical calculations. Previous ISS experiments have shown that microgravity dusty plasmas can undergo a transition from homogeneous liquid to a filamentary solid, reminiscent of the one occurring in electrorheological colloidal suspensions. However, our analysis suggests that the filamentary dusty plasmas in PK-4 transition to a mesophase intermediate between liquid and solid, i.e., a liquid crystalline phase. Specifically, we demonstrate that the coupling between dust particles within filaments is crystal-like, while the coupling across filaments is liquid-like. In addition to a common orientation along a director axis (nematic behavior), the dust filaments also appear to align in large-scale nested structures, or shells (smectic behavior). Finally, the dust filaments are found to arrange in hexagonal patterns in the plane perpendicular to their director axis, suggesting the possibility of a smectic-B or smectic-C state. Based on these findings, we discuss how microgravity filamentary dusty plasmas can be used to study fundamental open questions related to universality of phase transitions, pattern formation, and defect propagation in liquid crystals. |
Thursday, October 20, 2022 10:00AM - 10:30AM |
TI02.00002: From a charged particle to basic thermodynamics Invited Speaker: Dietmar Block It's almost 30 years ago that plasma crystals have been discovered. Since then the field of dusty plasma has made significant progress and many fundamental processes in strongly coupled systems have been observed and analyzed. During the past few years a number of new and powerful diagnostics have been developed which enable measurements on a new level with respect to precision and thus allow us to tackle problems which where inaccessible before. This talk starts with an introduction to light scattering at a single particle and how this can be utilized to determine particle size, particle charge and other particle properties [1]. It thus addresses an old but still unsolved problem in plasma physics: floating objects in a non-collisionless flowing plasma environment. The second part of the talk will focus on many particles systems and how thermodynamic approaches like configurational temperature [2] and thermal motion can be used for advanced diagnostics. It is shown that even entropy can be measured directly [3,4,5]. |
Thursday, October 20, 2022 10:30AM - 11:00AM |
TI02.00003: Coherent microwave scattering for diagnostics of small-size plasma objects Invited Speaker: Alexey Shashurin Measurements of electron number density in small-size plasmas are very challenging as many traditional diagnostic approaches cannot be used. The coherent microwave scattering (CMS) offers a convenient diagnostic solution for such small plasmas. It is based on measurement of the total number of electrons present in a small plasma object using the constructive coherent elastic scattering of microwaves. Scattered radiation can be detected and attributed to the absolute electron count in the plasma after appropriate system calibration with dielectric scatterers. |
Thursday, October 20, 2022 11:00AM - 11:30AM |
TI02.00004: How sheath properties change with gas pressure: modeling and simulation Invited Speaker: Lucas P Beving Sheaths regulate how plasma affects material surfaces, making properties of sheaths important in applications like etching and implantation. Properties that are often studied are the values of the ion velocity, plasma density, electric field, and potential at the sheath edge. Current models for each of these properties account for the effects of charge-neutral collisions, which is useful since devices operate over a range of gas pressures. However, experimental validation of these models is limited, generally to low pressures (~1 mTorr), where diagnostics like laser-induced-fluorescence and Langmuir probes work well. We design a two-fluid model to estimate each sheath property at varying pressures and test the model with1D particle-in-cell simulations. The simulations include charge-neutral collisions through the direct simulation Monte Carlo method and are a first step in validating collisional sheath models. We solve the two-fluid model numerically to compare with the simulations and find they generally agree over a wide pressure range (0.01-10,000 mTorr). Both predict the ion velocity (collisional Bohm speed), and the density relative to the bulk density decrease with increasing pressure, while the sheath potential drop and sheath width increase. The electric field is constant in both. However, the two-fluid model lacks kinetic effects, like non-Maxwellian features of the electron velocity distribution and temperature gradients. We find that the former leads to small differences between the model and simulations at low pressures (<100 mTorr), while the latter leads to larger differences at the highest pressures (>100 mTorr). We derive expressions for each property that depend only on pressure and include kinetic effects. Our simulations show that collisions modify the sheath properties as predicted by a collisional sheath model. |
Thursday, October 20, 2022 11:30AM - 12:00PM |
TI02.00005: Bohm Criterion of Plasma Sheaths away from Asymptotic Limits Invited Speaker: Yuzhi Li Sheath theory has a central place in plasma physics as its original |
Thursday, October 20, 2022 12:00PM - 12:30PM |
TI02.00006: Study of the Taylor scale and intermittency in broadband magnetic fluctuations in a magnetized turbulent plasma wind-tunnel Invited Speaker: Carlos A Cartagena-Sanchez Turbulent magnetic fluctuations are ubiquitous in both astrophysical and laboratory plasmas that exhibit power-law broadband fluctuations and intermittency. Power-law like broadband fluctuations indicate an energy-cascade where energy is injected at large scales and cascades to smaller and smaller scales where energy is ``dissipated'' via some mechanism. Intermittency in the magnetic fluctuations is associated with current sheets or coherent structures. This talk focuses on understanding the dissipation scale and the intermittent behavior of the magnetic fluctuations. The fluid Taylor scale is investigated as a potential dissipation scale. The Taylor scale is obtained through multi-point correlations of broadband fluctuations. From the spatial and temporal correlations respectively, the measured Taylor scales are $2\pm cm$ and $3\pm 1cm$. Intermittency in magnetic fluctuations is investigated through a statistical analysis of temporal and spatial increments: the probability density function of increments and its moments, i.e. structure functions. |
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