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SECTION 3: SCIENTIFIC/TECHNICAL PROJECT DESCRIPTION A. Introduction to dusty plasmas A dusty plasma is a mixture of electrons, ions, and micron-size solid particles that are highly charged [1-15]. It can also contain neutral gas [16-18]. Particles used by experimenters are typically monodisperse polymer microspheres. These dust particles collect more electrons than ions, causing them to become highly charged [19-24], with typically -104 e for a 5-µm sphere. Dusty plasmas can sustain several kinds of waves, which have oscillatory motion that is restored by collective electric forces. In particular, we distinguish two kinds of waves: The dust acoustic wave is the wave of interest for this proposal. It is a longitudinal wave that is self-excited by flowing ions [25-43]. This wave is hydrodynamic in nature, and it is sustained by a macroscopic electric field arising from charge separation of the dust as compared to the electrons and ions. It does not intrinsically depend on the discreteness of individual dust particles. The lattice wave can be either longitudinal or transverse [44-51]. This lattice wave arises because of the microscopic electric interaction of individual dust particles, and it occurs in the strong-coupling regime, 1. This lattice wave is not the subject of the present proposal (although it is mentioned in a separate proposal by PI Bin Liu). As an experimental system, a dusty plasma has several attractions for the study of waves. Chief among these attractions is the ease of observing the wave using video imaging [52]. By illuminating a dust particle cloud with a sheet of laser light, the experimenter can image a crosssection within the volume of the cloud. The collection of dust particles has very convenient length scales (millimeters) and time scales (tens of milliseconds). Video imaging allows a measurement of the particle number density, which is proportional to the light-scattering brightness recorded in video images. B. Objective of this project We will perform experimental studies with nonlinear waves in dusty plasmas using the PK-4 instrument on the International Space Station (ISS). We seek to answer fundamental physics questions in the following experiments. These experiments have already been approved by the PK-4 Facility Science Team, and they have been identified in the PK-4 Experiment Science Requirements (ESR) document as experiments specifically for our Iowa group. Main Experiment: Synchronization of dust acoustic waves (DAWs): 1. Using sinusoidal manipulation: Goal #1: Can we extend the physical understanding of oscillator synchronization, to the case of propagating waves, using multi-wavelength experiments in dusty plasmas? Backup Experiment: In addition to the Main Experiment above, we also have an alternative “Backup Experiment.” The circumstances that would lead us to perform this Backup Experiment include: the PK-4 mission is extended. our Main Experiment experiences a technical problem, or it has a negative scientific outcome (its predicted phenomenon is not observed). the phenomenon for the Backup Experiment is fortuitously observed early in the mission, and we find that we can do the analysis quickly. Dynamical phenomena in binary mixtures: 2. In a 3D dusty plasma with two sizes of dust particles, with a DC field: Goal #2: Is the motion of dilute minority species particles governed by mobility? C. Need for microgravity (a) (b) 1g zero- g Fig. 1 Sedimention due to gravity is avoided by microgravity conditions, enlarging the dust cloud, as shown in these cross-sectional images of clouds of 3.4 m particles in the PKE instrument, under gravity (a) and microgravity (b) conditions [G. E. Morfill et al., Proc. of 55th International Astronautical Congress, 2004.]. The study of phenomena requiring finite distances, such as waves of multiple wavelengths or transport in 3D systems, is enabled by this enlargement of the dust cloud. This project requires microgravity because it is otherwise impossible to form a large 3D dust cloud and observe wave propagation for a distance of many wavelengths. With gravity, a dust cloud sediments to a few layers, Fig. 1(a) [53]. With microgravity, a much larger dust cloud can be formed, as in Fig. 1(b) [53]. The dust acoustic wave studied here requires a 3D dust cloud. Under 1g conditions, 3D dust clouds are very limited in size, as shown in Fig. 2(b), so that the dust acoustic wave propagates only about two wavelengths before it reaches the boundary [39,43]. Microgravity conditions enable experiments with a much longer 3D dust cloud, as in Fig. 2(a), which is an image from the PK-4 Commissioning Experiment. (a) 0 g ISS 5 mm (b) 1g 5 mm Fig. 2. Size comparison of the 3D dust cloud in the PK-4 flight experiment (a), and ground-based experiments (b). The PK-4 data are from the commissioning experiment aboard ISS. (The image in (a) is split because the dust column is so large that it requires two cameras.) The groundbased data are from our lab [39]. Both (a) and (b) show the presence of a dust acoustic wave in the dust clouds. Microgravity enables experiments with large number of wavelengths. Besides avoiding sedimentation, microgravity also enables the observation of the phenomena driven by some weaker forces that are obscured by gravity. Under 1 g conditions, ion drag is an order of magnitude smaller than the gravitational force. Under 0 g conditions, effects of the ion drag force are easily seen, as they balance the electric force QE. The strength of this ion drag force is not in proportion to the electric force, so that a force imbalance can act on one size of particles, but not another [55-60]. Our optional mobility experiment will exploit this imbalance by making a minority-size particle to drift through the center of a dust cloud, allowing a detection of mobility-limited motion. D. Experiment approach and PK-4 features used in this project Our experiment requires a dust cloud that is three dimensional, can be imaged, and can be manipulated. The PK-4 instrument meets all of these needs. The PK-4 instrument [54, 61-72] is a multi-user facility provided by the European Space Agency. It has been on-orbit in the International Space Station (ISS) since October 2014. Our sketch of the PK-4 instrument, Fig. 3, shows its major scientific features. A U-shaped glass tube is evacuated and filled at low pressure with neon (or argon) gas. This gas is partially ionized by applying a high voltage to a pair of electrodes, called the active and passive electrodes. This voltage can be either DC or a polarity-switched DC that alternates the direction of the electric field. Dust particles are introduced by agitating dispensers, which are filled with several sizes of polymer microspheres. When these microspheres (which we term dust particles) enter the plasma, they rapidly gain a large negative electric charge. Due to this charge, these dust particles are electrically trapped in the plasma. The dust particles do not touch one another, but maintain an interparticle distance of about 0.2 to 0.5 mm. TM thermal manipulator EM EM electrode RF1 RF2 movable RF coil fixed RF coil D1~D3 gas jet particle dispenser D4~D6 shake particle dispenser HV high voltage with polarity switching Fig. 3 PK-4 flight model on the ISS. The U-shaped glass tube plasma chamber is powered via a pair of DC electrodes mounted on the ends of two glass legs. Dust particles can be trapped in the straight portion between the two legs, where the “positive column” of the gas-discharge plasma is located. The main diagnostic on PK-4 is a pair of video cameras, which image the dust cloud. These “particle observation cameras” are mounted on a movable optical stage, along with optics that generates a sheet of laser light to illuminate a cross section within the dust cloud. There are two cameras, and not just one, because the dust cloud is so long. Manipulation devices on PK-4 include several features that we may use for our synchronization experiment. These include function generators that can modulate voltages applied to the DC electrodes, a third electrode termed the “EM electrode,” or a pair of radiofrequency (RF) coils. These function generators can be modulated at frequencies that are convenient for our synchronization experiment. The power supplies for operating the PK-4 plasma allow a choice of DC or polarity switching. When operating with a DC high voltage, the dust cloud will tend to drift to one end of the tube, where it will be lost to the vacuum port; this loss of the dust cloud can be stopped by “trapping” the cloud. At the time we wrote this proposal, Core-Team members of the PK-4 Science Team were performing commissioning experiments to identify the best operating conditions for trapping, for example by applying power to the RF coil to plug the dust cloud. Operating with a DC high voltage is useful for certain purposes, including the strong selfexcitation of dust acoustic waves, which takes place due to a DC ion current driven through the plasma. If we operate with polarity switching, we will use a duty cycle different from 50%, so that there remains a net DC ion current that can excite the dust acoustic wave. The feasibility of our Main Experiment, to study synchronization, is very promising: It is already demonstrated that PK-4 readily exhibits the dust-acoustic wave, when the gas pressure is low enough. It has been observed many wavelengths, as is required for our wave synchronization experiment. (See Fig. 2(a), where we show an image from Commissioning Experiment of PK-4 on board the ISS.) The required ion flow, which is needed for self-excitation of the wave, is easily attained in PK-4 using well-established operating conditions, with a DC current of typically 1 mA. We have already performed extensive ground-based experiments to establish that the phenomenon of synchronization can be studied using the proposed experimental protocol and analysis methods. The experimental parameters required in our task will be well within PK-4 capability. Typical values include: a gas pressure of less than 50 Pa Neon to allow wave excitation, 1 mA current, DC operation or operation with < 50% polarity switching duty cycle, camera operation at < 100 frames/sec, and formation of large clouds with particles of one size (or two sizes, in the case of our mobility Backup Experiment). PK-4 features used in this project Imaging. Using the particle observation cameras with the illumination laser sheet, we can observe a cross-sectional slab of a 3D particle cloud, Fig. 4(a). For the purpose of our Main Experiment on wave synchronization, we will not require particle identification, but will instead measure particle number density. We do not require absolutely calibrated number density for most purposes, but instead only a relative number density, which we will measure using the brightness within an image, the same method we have demonstrated in our ground-based experiments with dust acoustic waves [35,37,39,43]. Nevertheless, if we do wish to report the absolute number density, we can do this using our recently developed analysis method of extracting the 3D number density from 2D images; we published this method in 2015 in Review of Scientific Instruments as part of our preparation for PK-4 [73]. (a) (b) Fig. 4 (a) PK-4 image from Science Campaign 1, showing a cross-sectional image of the 3D dust cloud. (b) At Iowa, our analysis of this image yielded these identifications of particles and their x-y coordinates; the circles represent positions in one video frame, and the dots in the next consecutive frame. Velocities can be determined by subtracting these consecutive particle positions. A particle “thread” is lost when a particle is not found in the next frame due to motion in the 3 rd coordinate. For our alternative Backup Experiment, we will use our PTV method to identify particles and measure their velocities. We have already performed a feasibility test, using PK-4 flight data, to verify that our PTV method will work with PK-4 images; these preliminary test results are shown in Fig. 4(b). Particles. Our Main Experiment requires just one size of particles. The particles will be injected using the standard PK-4 operating methods with a shaker dispenser. Our Backup Experiment, however, requires particles of two different sizes; if we perform that Backup Experiment we will first fill the particle cloud with one size, using a shaker dispenser, and then slowly introduce a few “minority” particles of a different size, which will migrate to the central axis of the plasma. These minority-size particles will be introduced by a gas jet dispenser, which was found in the first commissioning experiment to be capable of introducing small numbers of particles, according to our conversation with a Russian Core-Team member. Electrical manipulation. In our wave synchronization experiment, we will manipulate our dust particles electrically to excite waves. We will test three ways of modulating the plasma density or ion current: DC discharge current, EM electrode current, RF coil power. In all three ways, we will apply the modulation using a function generator, controlled by the experimental script. The way that these manipulation devices affect the wave, to cause synchronization, is generally global, and not local: The DC and EM electrodes are very similar to the manipulation electrodes we have successfully tested in our ground-based experiments [39,43]. They are in effect like large Langmuir probes, which can extract an ion current or electron current from the plasma. This current extraction can be so large as to meaningfully modulate the plasma density. This density modulation, in turn, has several effects: it can cause a variation in the dust charge due to depletion effects, and it can cause a disturbance in the large-scale electric ambipolar electric fields. The dust cloud is sensitive to all these effects. By sinusoidally modulating such a manipulation electrode, we have verified that we can cause synchronization of the dust acoustic wave, in our groundbased tests [39,43]. The RF coil will have the opposite effect of introducing additional plasma density. Increasing the current through the coil will cause an enhanced location ionization, and an enhanced local plasma density. The ambipolar electric field will be altered by this enhanced ionization, so that ions are pushed away from the RF coil region. The frequency of the RF coil is high, but it can be modulated at a low frequency, comparable to the frequency of the dust acoustic wave. All three manipulation devices can be modulated sinusoidally, using the PK-4 function generators, at an adjustable frequency and amplitude, as required for the synchronization experiment proposed here. E. Our previous work on the PK-4 project Our group has focused for several years on preparing for the PK-4 mission. PI John Goree has participated in many meetings of the PK-4 Facility Science Team since 2008, as well as workshops at CNES for planning the payload operations. Dr. Liu has performed computer simulations since 2012 to test concepts for our PK-4 experiments, leading to six refereed publications specifically for planning for PK-4. These publication topics include image analysis methods [73], waves and shear-induced motion experiments [74,75], and mobility experiments [58-60]. In these simulations, Liu used PK-4 parameters for charge, gas pressure, and particle size. Liu and Goree have also built the Iowa ground-based model of PK-4, Fig. 5; this model exactly copies the plasma tube for PK-4, and it uses the same model of cameras for particle observation. Our laboratory also has other breadboard plasma chambers, which we have used to develop the experimental plans proposed here. These tests include demonstrations of wave synchronization [39,43]. The analysis methods developed for those papers will serve us as we Fig. 5 Iowa ground-based model of PK-4. analyze PK-4 flight data for 3D dusty plasmas. F. Fundamental physics questions we seek to answer in our experiment 1. Main Experiment: Synchronization of dust acoustic waves (DAWs) Goal #1: Can we extend the physical understanding of oscillator synchronization, to the case of propagating waves, using multi-wavelength experiments in dusty plasmas? Synchronization is a cooperative phenomenon widely observed in nature, from biological, chemical and physical to social systems [76,77]. A signature of synchronization is a shift in the frequency of an oscillator or wave. This frequency shift occurs due to a combination of nonlinearity and external modulation. Oscillators were the original topic for studying synchronization, starting with Huygen’s pendulum clocks in 1665 [76]. Other examples of synchronized oscillators include heart pacemakers [78,79], chaotic laser array [80,81], and interacting vortices within a superconductor [82,83]. The understanding of oscillator synchronization has matured, with well developed theories such as the van der Pol oscillator model [84]. Wave synchronization, on the other hand, is not a mature topic; it is not well understood; it lacks suitable quantitative models. Waves are more complicated than point-like oscillators because they oscillate not only in time but also in space. Waves are also complicated by the effects of dispersion, i.e., the dependence of the wave’s speed on its frequency. Oscillators have no effect comparable to dispersion, because they have no propagation speed. Plasmas of all kinds support a wide variety of waves [85,86]. At large amplitude, these waves become nonlinear, and exhibit phenomena such as synchronization [87-96]. Dusty plasmas are particularly well suited for a study of wave synchronization because they meet four essential requirements: a self-excited wave, nonlinearity, ease of modulation, diagnostics for wave motion. The dust-acoustic wave (DAW), which is a lowfrequency compressional wave, somewhat like a sound wave, is self-excited by an ion flow [25-43]. Its frequency and wavelength are typically about 10 Hz and 3 mm. The number density varies in this wave, and can reach a large amplitude, as can be seen in Fig. 6. Modulation of the dusty plasma is easily accomplished by applying sinusoidal voltages to an electrode. The diagnostic for detecting the wave motion is video imaging, which provides the required spatial and temporal description of the wave’s amplitude as it propagates. Fig. 6 Dust acoustic waves (DAWs) in a PK-4 parabolic flight [Fortov et al., 2005], Ground-based experiments, by our group [39,43] for a cloud in a dc plasma at 70 Pa neon. and other groups [31,33,36,42], have not only The wave attains such a high amplitude confirmed that synchronization of the DAW occurs, (>50% modulation of number density) so they have also revealed several new phenomena. The that the wave is nonlinear. discoveries of Ruhunisiri and Goree [39,43] include our proposed research topics: branching and thresholding of a synchronized state, and a newly observed nonharmonic synchronization state. The need for microgravity arises from the very limited spatial extent of the ground-based experiments. Due to sedimentation, the dust clouds in ground-based experiments have a finite size, limited to about three wavelengths, as seen in Fig. 2(b). The observations of waves propagating such a short distance are heavily affected by boundary conditions and nonuniformities in the dust density. We can overcome these limitations by using microgravity conditions to suppress sedimentation, allowing the DAW to propagate large numbers of wavelengths in relatively uniform background conditions. Among all possible microgravity platforms, PK-4 is ideally suited for this purpose: it not only meets all four requirements for the study of wave synchronization – it meets them under very favorable conditions: The self-excitation of the DAW has already been confirmed in PK-4’s Commissioning Experiment. See Fig. 2(a). The wave reaches nonlinear amplitudes as seen in Fig. 6, where the number density varies from crest-to-trough by an order of magnitude. Several kinds of electrodes are provided with function generators that can drive varying frequencies and amplitudes of modulation. The cameras provide the required diagnostics. The particle-observation cameras will be the main diagnostic, while the glow camera will help as well in monitoring the modulation of the background plasma conditions. Our scientific goal is to: investigate three unexplained phenomena, which we recently discovered in our groundbased experiment. These phenomena are a nonharmonic synchronization state, thresholding, and branching, as we explain below. provide the data required to develop and test theoretical descriptions of the spatiotemporal character of wave synchronization. We will obtain space-time diagrams of the dust number density, which can be compared directly to solutions of nonlinear wave equations for dust density. Experimental plan: In our first mission we will perform a preliminary experiment to test various modulation schemes, and to define the required conditions and procedures: We will perform brief runs with three kinds of manipulation electrodes on PK-4: the EM electrode, DC electrode (active and passive), and the RF coil. All three of these can be driven by function generators at specified amplitudes and frequencies, as required for synchronization experiments. We will identify the best of these three modulation devices to use in the second mission. We will also perform a coarse-grained parameter search, to identify ranges of frequencies and amplitudes to use in the second mission. This preliminary experiment will require roughly 10 minutes of observation time. In our second mission, we will improve our experiment to generate our publishable data. The experiment will use two kinds of scans: In our first scan, we will explore the nonharmonic synchronization state and other synchronization states. We will do this by stepping the modulation frequency over ~50 values, all at a fixed amplitude. This scan will require about 2.5 minutes of recording time, based on our ground-based Fig. 7. Example space-time diagram, from our experiment. ground-based experiment [43]. A darker color In our second scan, we will investigate the indicates a higher number density n for the dust. branching and thresholding of the 1:1 synchronized state. Following the protocol we developed for our ground-based experiments, this will be done by smoothly sweeping the frequency over a 15 Hz range in an inner loop, and stepping the amplitude upward in an outer loop with 14 levels. These sweeps will require 9.5 minutes. In both missions, we will record image data using the PK-4 particle observation camera. This camera has a suitable resolution of 13.9 m/pixel, almost the same as the 12.8 m/pixel resolution in our ground-based experiment. While the PK-4 cameras can also operate up to 200 fps, we will plan on a lower frame rate to conserve resources. We estimate that 100 fps will provide a sufficiently high Nyquist frequency to detect the harmonics. Analysis plan: Fig. 8 Example data, from our ground-based experiment [39], showing synchronization states at wave frequencies that are a multiple of rational number of the modulation. The observed spectrum is below 50 Hz, so that sampling at 100 fps would be adequate. We will use analysis methods that we developed for our previous ground-based experiments. We start by preparing space-time diagrams from the gray-scale images in each frame from the particle observation camera. We average over the coordinate perpendicular to the wave propagation, so that dust density data are reduced to two coordinates n(x,t). An example space-time diagram is shown in Fig. 7. (Note that in these ground-based data the spatial distance ranges only over two wavelengths, which we will greatly improve upon by using PK-4.) We will use the space-time diagram to prepare our two main graphs: power spectra and Arnold diagram. Using the data from our first scan, we will prepare power spectra graphs, as in Fig. 8. These are prepared by Fourier transforming the time series of dust density, for a specified position in the space-time diagram. This power spectra method is different from the Hilbert transform method used by Williams [42], and correspondingly it is useful for different scientific purposes. Our purposes are to identify the various nonlinear states, both harmonic and nonharmonic, and to reveal small features such as sidebands. The signature of the nonharmonic state, in Fig. 8, is a spectral frequency that does not vary linearly with modulation frequency. Using data from our second scan, we will prepare an Arnold tongue diagram, as in Fig. 9. This is a graphic representation to indicate a binary condition, whether synchronization occurs or not, as two modulation parameters are varied. Our purposes in using the Arnold diagram will be to investigate branching and thresholding, which are visible in the example of Fig. 9 from our ground-based experiment. At amplitudes below the threshold level, synchronization does not occur — using PK-4 we will determine whether this is due to frictional dissipation or whether it is merely an artifact of the small sample volume in ground-based experiments. For the branching Fig. 9 Example Arnold diagram, from our phenomenon, we will test two explanations: ground-based experiment [39], showing either the branches are part of the same 1:1 synchronization states as shaded regions in a synchronized state, or they indicate a merging of parameter space for the external driving amplitude and frequency. two different synchronized states. Theoretical support for the experiment: A theoretical effort will be undertaken to meet a need for the experiment: providing a suitable theory for synchronization of propagating waves, to compare to the experiment. The theory effort has two components: The largest effort will be analytic theory, carried out at NRL, under separate funding, under the leadership of Dr. Ganguli. Details are provided in Ganguli’s proposal. A complementary effort will be numerical simulations performed at the University of Iowa, under the funding proposed here. These simulations at Iowa will be done by Professor Abhijit Sen, assisted briefly by a postdoc. Two models will be used: (i) A hybrid fluid model. The dust, electrons and ions will be considered as each being a continuum, sharing the same volume. The dust will be modeled with full equations of continuity and momentum, so that its density and flow velocity will be fully evolved in space and time. To provide for the disparate time scales, electrons and ions are assumed to have Boltzmann distributions. One of the outputs of the model is the spatio-temporal evolution of the dust number density, which is the same quantity obtained in the experiment using cameras. This will allow a direct comparison of the model to the experiment. The dust momentum equation will have an additional electric field term (that has both spatial and temporal variation) to represent the external driver, mimicking the modulation in the experiment. The dust dynamical equations will be cast in the form of first order convective differential equations and solved using the flux corrected scheme as developed by Boris et al [97]. The electron and ion density contributions will be updated by solving the Poisson equation at each time step to determine the electrostatic potential. Such a full-scale fluid simulation with appropriate boundary conditions will provide a realistic tool to interpret the experimental results and also help validate the fKdV model that will be developed at NRL under separate funding. It should be mentioned that our hybrid model can be efficiently solved by using the LCFCT code [97] and has been employed for a number of studies in the past [98,99]. As a validation of the Sen et al. model, this hybrid code has been used successfully already for ion acoustic precursor solitons [100]. (ii) Molecular dynamics simulation. The equations of motion will be integrated for point particles interacting through Yukawa potentials. The purpose is to account for the effects of discreteness of the dust particles. The lighter electron and ion species will be incorporated through a shielding factor in the interaction potential – namely the Yukawa potential, i.e., the ‘dressed particle’ approach of Joyce et al. [101,102]. The simulations will be carried out using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [103] open source code, initially in a two dimensional periodic system and later extended to a fully threedimensional system. The code has been successfully employed in the past to study nonlinear excitations in a dusty plasma medium [104]. These simulations will help provide some parameters for the dust equation of motion in the hybrid fluid model. The theoretical effort will be coordinated in two ways. First, all the theory will be done in close coordination with experiment, so that the theory includes the proper physical processes, parameter values, and boundary conditions. This will be accomplished by having Prof. Sen carry out his work while at The University of Iowa. Second, the two theoretical efforts, analytic and numerical, will be coordinated; this will be done by frequent communication between Prof. Sen at the University of Iowa and Ganguli’s group at NRL. This communication will come easily, because Ganguli and Sen already correspond frequently on other projects. 2. Backup Experiment: Mobility in a DC field We next describe an experiment available to us, as an alternative, in the unlikely case that problems arise and our Main Experiment is found to be impractical. This experiment was approved July 2014 by the PK-4 Facility Science Team for inclusion in the Experiment Science Requirements document. Goal #2: Is the motion of dilute species particles governed by mobility? Fig. 10 Our simulation on the mobility of a When a different size of dust particle is single particle in a 3D dusty plasma, under PK-4 introduced into a dusty plasma, under microgravity conditions [58]. Shown here are coordinates of conditions, it typically settles at the center or edge particles in a portion of the dust cloud. of the dust cloud [56,57,105-109]. We will exploit this separation tendency by introducing a very small number of different-size particles (projectiles) into the center of a pre-existing dust cloud (target). In the presence of a DC field, we expect that the projectile particles will drift slowly through the target, with an average velocity that we will measure. This average velocity will be the result of a balance of a net force (difference of electric and ion drag forces) and a drag due to fraction of particles Coulomb collisions with the target. Microgravity is essential for this experiment because otherwise, in a 2D ground-based experiment, the differently sized projectile particles will separate from the target, while in 3D they can remain along the central axis of the plasma. This experiment differs from the “lane formation” experiments planned by other PK-4 experimenters because our projectiles will be dilute. We will inject so few projectiles that one projectile will not influence the motion of another, as is the case with lane formation [56,57]. To prepare for this experiment, and to establish theoretical predictions for comparison to experiment, we have performed and published 3D simulations [58-60]. We used PK-4 conditions, and tracked the motion of a differently sized projectile as it drifted through a target cloud of particles, Fig. 10. Our scientific goal is to: verify the projectile drift is mobility-limited. The experimental plan’s first step will be to form a steady dust cloud (target) with no waves or flows. We require a DC field, with the dust cloud trapped by an application of the RF coil or other means. In the second step, we will intermittently inject small numbers of particles (< 100/second) of another size (projectiles). The projectiles will be imaged as they drift down the axis of the plasma. We will plan the time requirements using our MD simulation data; our preliminary estimate is 10 minutes of camera time. Our analysis method will start with particle identification to track particles at least two frames. (Our analysis of early PK-4 flight data indicates that we can do this typically for up to 100 frames, as shown in Fig. 11.). We will then obtain the Fig. 11. Our analysis of early 1 drift velocity, calculated simply data from the Science as the average velocity for Campaign 1 experiment on PK-4 aboard ISS, showing particles. If we find that the that we can track individual drift velocity is constant, this dust particles for typically up will suggest that motion is 0.1 to 100 video frames. The mobility-limited. As a check, vertical axis of this graph is we can compare the the fraction of particles that can still be identified uniquely instantaneous fluctuations after the indicated time has (about the average velocity) to elapsed. the fluctuation levels observed 0.01 0 200 400 frame number in our MD simulation. G. Relationship to other proposals The present proposal is related to a proposal “Understanding the Frequency Synchronization Physics in PK-4 Experiment” submitted by PI Gurudas Ganguli, of the U.S. Naval Research Laboratory (NRL). Ganguli’s proposal is theoretical. It will provide theoretical support for the present proposal, which is mainly experimental. The present proposal is scientifically separate from another proposal, “Three-dimensional dusty plasma experiments,” submitted by Bin Liu, with Goree as a co-I. The scientific goals of the two proposals are different. The two proposals also require that two separate flight experiments be performed, because they need different operating conditions. H. Broader Impacts K-12 outreach task The PI will give a presentation at an additional class in an elementary school. This will be done as part of the “Hawkeyes on Science” program, which provides equipment and a truck. The goal is to generate excitement about science. This presentation will be given to one class, in addition to the presentations that the PI will give for his current DOE grant. The presentation will center on sedimentation and buoyancy, and how the International Space Station allows scientists to avoid these conditions. Interdisciplinary research This research has an overlap with nonlinear dynamics as well as other plasma physics areas Graduate education A graduate student will be supported for participation in the experiment and data analysis. Goree, on a K12 outreach, May 2014. Two classes of fifth graders to discover, with hands-on experiments how cool gases sink while warm gases rise due to buoyancy. Fifth graders respond well and show their excitement, as seen here. Broad dissemination of results Research results are disseminated in journals, conferences, a website, and a Twitter account. When possible, the peer reviewed journals used will be open-source.