Perspective: The dusty plasma experiments a learning tool for physics graduate students
PPerspective: The dusty plasma experiments a learning tool for physicsgraduate students
Mangilal Choudhary a) Institute of Advanced Research, The University for Innovation, Koba, Gandhinagar, 382426,India
The plasma is an ionized gas that responses collectively to any external (or internal) perturbations. Intro-ducing micron-sized solid dust grains into plasma makes it more interesting. The solid grains acquire largenegative charges on their surface and exhibits collective behavior similar to the ambient plasma medium.Some remarkable features of the charged dust grain medium (dusty plasma) allow us to use it as a modelsystem to understand some complex phenomena at a microscopic level. In this perspective paper, the authorhighlights the role of dusty plasma experiments as a learning tool at undergraduate and post-graduate physicsprograms. The students could have great opportunities to understand some basic physical phenomena as wellas to learn many advanced data analysis tools and techniques by performing dusty plasma experiments. Howa single dusty plasma experimental device at a physics laboratory can help undergraduate and post-graduatestudents in the learning process is discussed.
I. INTRODUCTION
When the gas is subjected to a strong electric field, gasatoms get ionized and the gas phase transforms into anionized gas phase. This ionized gas consists of equal num-bers of positive (ions) and negative charges (electrons) ifthe gas is completely ionized. Above a threshold den-sity of charged species (electrons and ions), the chargedparticles interact via long-range Coulomb interaction andcapable to exhibit the collective response to an externalfield similar to other phases of matter. Therefore, theionized gas medium, named plasma, is considered as thefourth state of matter . In laboratory experiments, thegas is often partially ionized therefore a large number ofneutral atoms present along with the electrons and ions.What does happen if sub-micron to micron-sized solidparticles are introduced into the plasma? As these solidparticles come into contact with the plasma, they acquirenegative charges on their surface due to the collection ofhigher electron current than the ion current. The roleof dust grains in plasma depends on the concentrationor density of charged dust. In the case of very low dustdensity, well separated charged dust particles only mod-ify the characteristics of ambient plasma and it is namedplasma with impurity (or dirty plasma). In the secondcase where dust density is high, charged dust particlesexperience the long-range Coulomb interaction and ex-hibit the collective response to the force field. In thiscase, plasma is named as dusty plasma .In laboratory plasma, massive dust particles ( M d ∼ − to 10 − Kg) acquire large negative charges theorder of 10 -10 of electron charge . Therefore, thedust grain medium has some remarkable or extraordi-nary features to differentiate with conventional two com-ponents (electrons-ions) plasma. Firstly, a large amountof charge on the dust grain surface increases the aver-age potential energy of the dust grain compared to its a) Electronic mail: [email protected] average kinetic energy. The Coulomb interaction amongthe nearby charged dust particles determines the phase(solid, liquid, or gas) of the dust grain medium . Sec-ondly, extremely small charge-to-mass ratio ( Q d /M d ) ofdust grains leads to new plasma eigenmodes at very lowfrequency (1-100 Hz) . The dust dynamics at suchlow frequency can be visualized even with naked eyes,which allows us to study the dynamics of dusty plasmamedium at microscopic level . Due to these novel fea-tures of dusty plasma, it can be considered as a modelsystem to understand various phenomena happening inthe physical universe .It is well known that there is a physics laboratory forthe undergraduate and post-graduate physics programsin the academic institutions. The purpose of establishinga physics lab along with theoretical courses is to demon-strate the role of physics to understand physical phe-nomena through experiments. Students would learn todesign, develop, and perform experiments to understandphysics laws and naturally occurring phenomena aroundus. The practical work engages students to develop skills,understand the process of scientific investigation and de-velop their understanding of concepts of physics. In sum-mary, practicals in physical sciences at the graduate levelhave a great significance in the creating scientific temperand learning process of students.The physics laboratories for undergraduate and post-graduate courses are equipped with different experimen-tal devices. Most of the experimental devices are de-signed to understand some particular physical phenom-ena or physics law. In recent years, plasma experimentsare included in the postgraduate physics laboratories inhigher educational institutes around the globe with theaim to create a basic understanding of the fourth stateof matter (plasma) . It has been discussed earlierthat dusty plasma is created in the background of plasmamedium; therefore, the establishment of dusty plasma ex-perimental setup at the physics lab can provide moreexperimental opportunities for the undergraduate andpostgraduate students. The low-cost dusty plasma de- a r X i v : . [ phy s i c s . e d - ph ] F e b vice can also be used as an ordinary DC or RF plasmadevice without the dust particles.A single dusty plasma device can be used to demon-strate various basic experiments, for examples, the studyof waves and oscillations , diffraction of waves , Crys-tal formation, phase transition and vortex formation etc., with the modification in electrode configurations,discharge conditions, and discharge configurations (DCand RF discharge). Apart from this, an external electricand magnetic field can play a significant role to performthe experiments of vortex flow and rigid body rotationalmotion . This device could also be used to under-stand the image analysis tools using the Matlab, Pythonand ImageJ software to characterize the complex flowpatterns and spectral analysis of waves. In the absenceof dust particles (without dust), the same device can beused to perform the basic plasma experiments . Theplasma experiments help the student to learn about gasdischarges and the use of simple diagnostics to character-ize plasma. Since plasma is a highly non-linear system,the student can get various kinds of non-linear signals tounderstand the data analysis tools .The paper is organized as follows: Section II dealswith the detailed description of the dusty plasma exper-imental setup. The experiments on dusty acoustic wavesand opportunities for students are discussed in Sec.III. InSec.IV, diffraction of dust acoustic waves by a cylindricalobject and its application for understanding the diffrac-tion of sound waves are discussed. The experiments ondusty plasma Crystal and phases of dust grain mediumare explored in Sec.V. The vortex formation and rota-tional motion of dust grain medium in the absence andpresence of an external magnetic field are discussed inSec.VI. An opportunity to use the dusty plasma imagesin learning various image processing and image analysistools is explored in Sec.VII. In the absence of dust par-ticles, plasma is a highly non-linear system. A discus-sion on time-series data and data analysis techniques isgiven in Sec.VIII. A brief summary of the proposed dustyplasma experiments at graduate-level physics programsalong with concluding remarks is provided in Section IX. II. DUSTY PLASMA EXPERIMENTAL SETUP
A borosilicate glass tube or stainless steel (SS-304) ofappropriate inner diameter (5 cm to 15 cm), thickness(8 to 14 mm), and length (10 cm to 50 cm) along withsufficient radial ports could be used for making a dustyplasma experimental device (or plasma device) . TheAxial and radial ports of the tube are used for pump-ing, gas feeding, holding electrodes, pressure measure-ment gauges, and dusty/plasma diagnostics purposes. Ageometrical (3D) view of a typical dusty plasma setupmade up of a glass tube is shown in Fig.1(a). For plasmaproduction between two well-separated planar electrodes,either radio-frequency (RF) power source (P ∼
100 W)or direct current power supply ( V dc >
600 V, I dc > < − mbar. The relative pressure inside this vacuum chamberis measured using a Pirani gauge. A needle valve or massflow controller (MFC) attached to the vacuum chamberis used to feed required gas into the vacuum chamber toperform experiments . Apart from the glass or SS-304 vacuum (or experimental) chamber, an Aluminiumchamber can also be used to make a dusty plasma ex-perimental setup The view of the aluminum dustyplasma device is shown in Fig.1(b). This setup is cur-rently used to study the magnetized dusty plasma atJustus-Liebig University Giessen, Germany. Such table-top dusty plasma devices are more suitable to study themagnetized dusty plasma. It should be noted that thereare different types of dusty plasma devices which canalso be used to explore the physics at undergraduate orpostgraduate level.Once the plasma is produced in the vacuum cham-ber, dust grains are injected into the plasma volumeusing a dust dispenser. The dust particle can be sub-micron to micron-sized mono-dispersive glass (plastic) orpoly-dispersive particles of mass density ∼ gm/cm .The dust grains in contact with plasma acquire nega-tive charges order of 10 to 10 e − and confined nearthe sheath region by balancing upward forces (electricand thermophoresis forces) and downward forces (gravi-tational and ion drag forces) . Here e − is the chargeof an electron. The charged dust particles are illumi-nated by a combination of low power red or green laser(30 to 100 mW) and plano-convex lens. The scatteredlight coming from charged dust particles are capturedusing a high frame rate ( >
20 fps) and high resolution( > is shown in Fig.2(a). A schematic dia-gram of dusty plasma experiments in radio-frequency (or DC) discharge configuration is depicted in Fig.2(b).The captured video or frames by CCD or CMOS cam-era are stored on PC for further analysis. Computer-based software such as Videomach, ImageJ along withthe MATLAB, Python image processing tools is used toanalyze stored image data (or frames) for further un-derstanding the dynamics of dusty plasma medium. .Sometimes different diagnostics such as Langmuir sin-gle probe , double probe and emissive probe canbe used to characterize the backgrounds plasma of dustgrain medium. III. DUST ACOUSTIC WAVES
Wave in the gas, liquid, and the solid medium is animportant topic for physics students. They are generallyfamiliar with sound waves in different mediums whichare the results of the elastic displacement of the par-ticles of the medium about their equilibrium position.Since the motion of particles in the medium is forth and
X Y Z c m c m (3) (4) (6) (7) (8) (9) (10) (5) 100 Ω I d1 I d2 K Ω Ω Vacuum chamber Gas pumping and feeding Laser and Lens CCD camera Pirani Gauge (a)
CCD Camera Vacuum pump Dust dispenser Vacuum chamber Laser Mirror Optical Stand
Dusty plasma experimental setup (b)
FIG. 1. (a) A typical Dusty plasma device made up of glass tube. (b) A dusty plasma device made up of aluminium chamber .Such devices can be used to perform dusty plasma experiments in the absence or presence of an external magnetic field. back along the direction of propagation of waves, thesound waves are the longitudinal waves. A typical soundwave in a gas medium is displayed in Fig.3(a). Similarto the well-known mediums, dusty plasma medium alsosupports very low frequency ( <
100 Hz) acoustic modes(DAW) . This novel feature of dusty plasmaattracts undergraduate and postgraduate students to un-derstand the wave motion in any medium (gas, liquid,and solid) by performing experiments on dust-acousticwaves in dusty plasma device.The excitation of dust-acoustic waves in dustyplasma device is possible in direct current (DC) dis-charge as well as in radio-frequency (RF) dischargeconfigurations . A schematic diagram of exper- imental dusty plasma setup (DC and RF discharge) tostudy the acoustic waves is shown in Fig.2. The dustacoustic waves excited in the DC discharge configurations(Fig.2(b)) are displayed in Fig.3(b). The possible causesfor excitation of DAWs include ion-streaming instabilityand dust-acoustic instability are discussed in detail in thereferences . In Fig.3(b), bright vertical bands (or redbands) are nothing but the compressed wavefronts of theDAW, and the dark region (or low dust density region)corresponds to the rarefaction regions. Since the inten-sity of a bright band (wavefront) is proportional to thedust density, the intensity plots along the propagation di-rection at different times help to obtain the wave param-eters such as wavelength ( λ ), phase velocity ( v d ), and fre- (8) (7) (1) (2) (5) (4) (5)
100 Ω I d1 I d2 (3) Ω X Y Z (6) (a) (9) (1) (2) (6) (3) (7)
Y Z X (4) (8) (5) (b)
FIG. 2. (a) A double anode configuration using DC power source to produce dusty plasma. (1) and (3) anodes, (2) cathode,(4) DC power supply, (5) CCD camera, (6) dust particles, (7) cylindrical lens and (8) red laser. The direction of current flowingbetween cathode and anodes is marked by arrows. (b) A schematic diagram of dusty plasma experiments which is operated byan RF power source. (1) Vacuum chamber, (2) upper transparent coated electrode, (3) lower metal electrode, (4) RF powersource, (5) dust grains, (6) and (7) CCD cameras, (8) mirror and (9) red laser. quency ( f d ). Intensity profile corresponding to Fig.3(b)is shown in Fig.3(c). In Fig.3(d), the intensity profiles ofDAWs at different times are plotted. For getting intensityprofile plots, one can use ImageJ (free available) software,Matlab and Python-based image processing and analysistools, some other image analysis tools. It is also possi-ble to get the space-time plots (see Fig.3(e)) using therecorded frames of propagating DAW with help of theMATLAB or Python. The space-time plots are used tocharacterize the dust acoustic waves .Apart from linear DAWs, various kinds of nonlinearwaves can also be excited in dusty plasma using thisdusty plasma device in DC discharge configuration .A single video frame of dust grain medium during thepropagation of nonlinear dust acoustic wave is presentedin Fig.4(a). In Fig.4(b), intensity profile of propagatingnonlinear wave (Fig.4(a)) is plotted. These both imagesare taken from the original paper of Merlino et al. .The nonlinear characteristics of the excited dust-acousticwave can be verified by fitting a harmonic function (sineor cosine) of the fundamental frequency ( f d ) and itsharmonics to the intensity profile of propagating DAW,which is shown in Fig.4(b). Space-time plots can also beused to get the frequency spectrum of propagating acous-tic waves through dust grain medium . One can alsoidentify the nonlinear characteristics of dust-acousticwaves based on the frequency spectrum obtained from space-time plots. There is also a possibility to modulatethe self-excited dust acoustic waves and excite thelinear and nonlinear waves in the dust grain medium byexternal forcing. In summary, it would be interestingfor undergraduate and postgraduate students to explorethe linear and nonlinear waves in the dust grain mediumthat relates the wave motion in a different medium. IV. DIFFRACTION OF DUST ACOUSTIC WAVES
Diffraction is an intrinsic property of the waves (me-chanical waves and electromagnetic waves) in any kindof medium or vacuum. It describes the change in thedirection of waves as it travels around an obstacle (bar-rier) or between a gap of the barrier. In daily life, wehear some noise (sound) of speaking persons from adja-cent rooms through door openings which is a result of thediffraction of sound waves. The diffraction or bending ofsound waves around an obstacle can be demonstrated bythe study of the water waves in a ripple tank (referencestherein ). The amount of diffraction (spreading or bend-ing) of the wave depends on the size of the object andthe wavelength of the wave.Instead of a water medium, a dusty plasma mediumcan be used as a model experimental system to demon- A typical sound wave (a) d = 370 V Z Y
Cathode
Anode (b) I n t e n s i t y ( a r b ) (c) t=0 ms Position (mm) P i xe l I n t e n s i t y ( a r b . ) t=15.2 mst=30.4 mst=45.6 mst=60.8 ms (d) (e) FIG. 3. (a) A typical sound wave in a gas medium. (b) A snapshot of dust grain medium in Y-Z plane while dust acousticwaves are propagating. (c) An average intensity plot of selected region in Fig.2(b) (top to bottom).(d) An average Intensityplots of same selected region (Fig.2(b)) at different times. It represents propagation of dust acoustic waves from anode tocathode. Fig.3(b)–(d) are reproduced from [Choudhary et al. , Phys. Plasmas 23, 083705 (2016)], with the permission of AIPPublishing. (e) A typical space-time plot which is constructed from consecutive 50 frames of DAWs using MATLAB script.
FIG. 4. (a) A snapshot of dust grain medium while waves arepropagating in direction of ions flow. (b) Average intensityprofile of dust acoustic wave in a selected region (rectangular)and a fitted non-linear harmonic function over the intensityprofile. Fig.4 is reproduced from [Merlino et al. , Phys. Plas-mas 19, 057301 (2012)], with the permission of AIP Publish-ing. strate the diffraction of sound waves around an obsta-cle. The diffraction of dust acoustic waves from a cylin-drical or spherical object can help to understand thediffraction phenomena of sound waves. It is possible tochange the wavelength of DAW by altering the dischargeparameters which help to understand the amount ofdiffraction around different sized cylindrical objects. Thedusty plasma experimental setup with a larger sized cath-ode ( >
10 cm) and smaller sized anode ( < Kim et al. reported experimental results on thediffraction of dust-acoustic waves by a cylindrical objectin weakly magnetized DC discharge plasma. In their ex-periments, the cathode was the grounded chamber andthe anode was a 2.5 cm diameter metal disk. In Fig.5(a),the DAWs appear as bright vertical fringes that prop-agate from anode to cathode. The diffraction of DAWaround a cylindrical rod (obstacle) was studied usingthe video images at different times . The bending ofDAW (diffraction) around the cylinder is shown in Fig.5(b). A ripple tank (shallow water waves in a tank) isconsidered a model to study the sound waves in two-dimensions (2D). Therefore, a more realistic simulation of the diffraction of sound waves in 2D can be obtainedusing a ripple tank. Image of a ripple tank simulation ofwaves (originating from a point source) interacting witha circular object is depicted in Fig.5(c). Since the dustacoustic waves and sound waves obey a similar set ofequations, the resulting diffraction patterns can be com-pared in both cases . Thus, a dusty plasma medium canbe considered as an excellent model system to learn thediffraction of sound waves at the graduate level in thephysics laboratory. V. CRYSTAL FORMATION AND PHASE TRANSITION
In solids, atoms or molecules are closely packed. Solidscould be either in crystalline or amorphous form. Incrystalline solids, atoms or molecules are arranged inan ordered (long-range order) pattern whereas atoms ormolecules have a short-range order in the amorphoussolids. The crystalline solids can also be categorizedinto single-crystal solids and poly-crystalline solids. Thepoly-crystalline solids consist of multiple single crystalregions (grains) and the boundary separating these re-gions is called the grain boundary. A unit cell (small-est repeating unit) is considered as a building block ofa crystalline solid. This unit cell is described by latticevectors (lengths of each side of the unit cell) and theangle between lattice vectors. The length of lattice vec-tors and angles between them differentiate the types ofunit cells of a crystal structure. X-ray spectroscopy isa diagnostic tool to explore the crystalline properties ofsolid materials. In the spectroscopic technique, one canget the diffraction patterns of scattered X-rays at differ-ent planes of crystal but difficult to realize the differentcrystal basis of three-dimensional (3D) crystals.For understanding the crystalline structure and phasetransition in solids at undergraduate and postgraduatephysics programs, a realistic model system is required.In dusty plasma experiments, it is possible to create aCoulomb crystal (2D and 3D) of micron-sized chargeddust particles. We term such structure a dusty plasmacrystal . One can see the dusty plasma crystaleven with naked eyes and can realize the periodic ar-rangement of the atoms in crystalline solids as shown inFig.6(a). White dots in both figures represent the dustgrains. An arrangement of dust particles in a 2D planealong a vertical direction is depicted in Fig.6(b) that rep-resent the types of dust crystal structures (bcc and hcp).The crystalline nature of dust grain medium is confirmedthrough the characteristics parameters such as Voronoidiagram and radial pair correlation function, g ( r ) .The dusty plasma experimental device either in DCor RF discharge configuration can be used to obtainthe dusty plasma crystal at an appropriate dischargeconditions . Using the freely available image anal-ysis software or tools, students can analyze the dustyplasma crystal properties and correlate the results to un-derstand the single crystalline, polycrystalline, and amor- Anode (a) (b) (c)
FIG. 5. (a) A single frame video image of dust acoustic waves in 2D plane without a cylindrical object. (b) Dust acousticwaves with the cylindrical object. A white rectangular on left side in both images is nothing but an anode. (c) Image of aripple tank simulation of waves (originate at a point source) interacting with a circular object in 2D plane. All images of Fig.5are reproduced from [Kim et al. , Phys. Plasmas 15, 090701 (2008)], with the permission of AIP Publishing. phous solids. By changing the discharge parameters suchas gas pressure and input power, the melting of crystal orphase transition can be understood by obtaining the ra-dial pair correlation function. The profile of g ( r ) againstradial distance ( r ) measures the phases of the dust grainmedium . Plots of g ( r ) in Fig.6(c) for different dis-charge conditions represent the solid, liquid, and gaseousphase of dust grain medium. VI. VORTEX AND RIGID ROTATIONAL MOTION
In daily life, we see the naturally occurring or inducedvortices in fluids such as whirlpools in rivers and torna-does. The vortices which are induced by any externalforce on a fluid element are termed forced vortices. Influids, such vortices can be induced by rotating a vesselcontaining fluid or by paddling in a fluid. For studyingthe naturally occurring vortices, a full understanding ofvortex behavior at the microscopic level is required. To demonstrate the vortex motion for graduate students inthe physics laboratory, dusty plasma can be consideredas a model system. In a dust grain medium, vortex mo-tion can be induced around a charged probe (metal wire)in unmagnetized RF discharge (see Fig.7(a)). An ex-ternal magnetic field can also be used to excite the vortexmotion in dust grain medium . Five consecutive still im-ages are used to reconstruct the image of Fig.7(b) whereone can observe the vortex motion in dusty plasma at agiven B-field. The free available particle image velocime-try (PIV) code and ImageJ software are very usefulto obtain the velocity profile of vortex flow and angularvelocity distribution of particles in a given vortex . APIV image corresponding to the vortex flow in the pres-ence of magnetic field is depicted in Fig.7(c). The dustyplasma device either in unmagnetized or magnetized RFdischarge configuration can be used to demonstrate thevortex motion in fluids. Students can visualize the vor-tex motion at particle level in the dusty plasma mediumand correlate these results to understand the vortices in (a) (i) (ii) (b) g(r) r (mm) g(r) r (mm) g(r) r (mm) (c) (i) (ii) (iii) FIG. 6. (a) a single video frame image of the Coulomb lattice of particles with about 10 micron diameter at power of 1 Wand pressure of 200 mTorr. They show the body-centered cubic (bcc) and hexagonal close-packed (hcp). (b) Relative positionof the particles in two adjacent planes in bcc (110) and hcp (001) structures. The particles in the next vertical plane arerepresented by filled circles while those in the original plane are shown by open circles. Images of Fig.6(a) and Fig.6(b) areReprinted from Physica A, 205 , J. H. Chu and Lin I , Coulomb lattice in a weakly ionized colloidal plasma, 183-190, Copyright(1994), with permission from Elsevier. (c) The normalized radial correlation function for a (i) solid, (ii) liquid and (iii) gaseousstate. Fig.6(c) is Reprinted from Advances in Space Research, 34, Smith et al. , Dusty plasma corellation function experiment,2379–2383, Copyright (2004), with permission from Elsevier. other fluids.Apart from the vortex motion, dust grain medium canalso be used to demonstrate the rigid rotational motionof any medium. In the presence of a weak magnetic field(B < .It provides a platform to learn the rotational motion ofmany-body systems by estimating the angular frequency of rotating particles. Students may come to know the dif-ferences in translation and rotational motion. A singleframe video image of an annulus dusty plasma is shownin Fig.8(a). The rigid body rotational motion of dustgrains in the region of an annual in the presence of B-field is estimated by a PIV image (see Fig.8(b)). A con-stant angular frequency variation along radial directionindicates the rigid rotational motion of medium . Thus, (a) (i) (ii) (iii) g Z Y (b) (c)
FIG. 7. (a) Eighteen overlapping video frames, side views, major ticks 2 mm. An RF voltage of 90 V (peak-to-peak) at pressure,0.5 torr were fixed during experiments. The probe (wire) was biased at 30 V. Three images (i)–(iii) were taken at differentheights (9mm, 8 mm, and 7 mm) of probe (white dot in image). These images in Fig.7(a) are reprinted with the permissionfrom [Law et al. , Phys. Rev. Lett. 80, 4189–4192 (1998)] Copyright (1998) by the American Physical Society. (b) A videoimage showing the vortex motion is reconstructed by the superimposition of five consecutive still images. An aluminum ringshaped electrode was used to confine dust particle. The yellow arrows represent the direction of vortex flow in this plane. Theexternal magnetic field of strength 0.05 T was applied along the discharge axis. (c) PIV image of the corresponding video imageof Fig.7(b)). This image is constructed after averaging the velocity vectors over 50 frames. The arrows indicate the direction ofrotation in a vortex and the color bars represent the magnitude of the velocity of the rotating particles. Fig.7(b) and Fig.7(c)are reproduced from [Choudhary et al. , Phys. Plasmas 27, 063701 (2020)], with the permission of AIP Publishing. dusty plasma experiments at the graduate level may in-troduce students to the concepts of rotational motion ofmany-body system and vortex flow in fluids.
VII. IMAGE PROCESSING AND ANALYSISTECHNIQUES
In dusty plasma experiments, the scattered lights fromthe solid charged particles are captured using a fast frameCCD or CMOS camera and image data (frames) aretransferred to PC. These stored images are later analyzedto get the dynamics of dust grain medium for given dis-charge conditions. It provides a platform to undergradu-ate and post-graduate physics students for understandingthe basics of image processing and image analysis tech-niques using various software and computational toolssuch as ImageJ, MATLAB, Python, etc. Using this dustyplasma device, students can get various kinds of dustyplasma data in form of images such as dust grain oscilla-tion, dust-acoustic waves, rotational motion, linear flowof dust particles, dusty plasma crystal, etc. They can use these images to learn various tools and techniquesfor analyzing images and calculate the dusty plasma pa-rameters which are helpful to understand the dynamics ofdusty plasma. A typical raw image of dust grain mediumand superimposition of six images (composite image) areshown in Fig.9. The superimposition of six images isdone with the help of ImageJ software. In other exam-ples, as shown in Fig.3(d) and Fig.7(c), MATLAB imageprocessing tools are used to get the intensity profile ofDAWs at different times and velocity profile of dust par-ticles respectively. Thus, such hands-on experience willhelp students gain a better understanding of the imageprocessing and image analysis techniques using ImageJ,MATLAB, Python, and other software.
VIII. TIME-SERIES DATA ANALYSIS
Students at the graduation level have knowledge ofnonlinear (complex) systems existing in the universe.Nonlinear systems exhibit sensitive dependence to theinitial conditions of the systems. For example, a dou-0 (a)
X Y (b)
FIG. 8. (a) Dust grains confined in an annular region between a metal disk and ring. The dust grains are confined betweenan aluminium disk of diameter 5 mm and ring diameter of 30 mm at electrodes voltage V up = 55 V, V down = 55 V and argonpressure p = 30 Pa. White dots represent charged dust particles . (b) PIV image of the rotational motion of dust grains inthe X–Y plane at magnetic field of strength, B = 0.4 T (image ref. ). (a) (b) FIG. 9. (a) A typical image of dust grain medium. (b) Image reconstructed by the superimposition of six consecutive stillimages correspond to fig.9(a). ble pendulum undergoing large oscillations. It is difficultto predict the exact future trajectories of the oscillator(double pendulum) . There are many natural physicalnonlinear systems such as atmosphere, weather, climatechange, wind speed, biological phenomena (blood pres-sure, heart rate), etc. The irregular temporal behaviorof the variables for a given system (time-series data) isan output of such complex systems with nonlinear feed-back loops and external driving force . It is required tounderstand and model such irregular fluctuations to un-derstand such highly nonlinear systems in the physicalworld. For understanding the nonlinear dynamical be-havior of complex systems, various times-series data anal-ysis methods such as fast Fourier transformation (FFT),phase space diagram, Lyapunov exponent, etc. are to belearned . A DC glow discharge plasma is assumed to be a highlycomplex non-linear system. It can be used as a non-linear system to understand other natural or artificialhighly nonlinear systems. The temporal irregular data(time-series data) in the form of discharge current orfloating potential of plasma (with or without particles)are recorded at a given discharge condition . Thepattern of the time-series data depends on the dischargeparameters such as gas pressure, discharge voltage, ex-ternal magnetic field, etc. In Fig.10(a), time-series data(floating potential) of a DC glow discharge plasma aredisplayed. The FFT of the same time series data isshown in Fig.10(b) from where one can obtain the valueof frequency of fundamental mode as well as higher-order harmonics . The harmonics appear with an inte-ger of the fundamental oscillation frequency which sug-1 (a) (b) (c) FIG. 10. (a) Time series plots of floating potential fluctuations at different values of magnetic field (fixed magnet).(b) Powerspectrum plots corresponding to the time series data of Fig.10. (c) Reconstructed phase space plots corresponding to the timeseries data of Fig.10. All Figures are reproduced from [Shaw et al. , Phys. Plasmas 24, 082105 (2017)], with the permission ofAIP Publishing.
IX. SUMMARY
In this perspective paper, the role of dusty plasmaexperiments in the learning process of undergraduateand post-graduate physics students at higher institu-tions/universities is discussed. I have proposed somebasic dusty plasma experiments like waves and oscilla-tions, diffraction of waves, crystallization, phase transi-tion, vortex motion, rigid rotational motion, and dataanalysis techniques to demonstrate some basic physicsexperiment, create a scientific temper among graduatestudents, and provide a platform for learning experimen-tal tools and techniques. How a single dusty plasmadevice either in direct current or radio-frequency dis-charge configuration can be used to perform various basicphysics experiments as well as to learn various image anddata analysis tools and techniques. A detailed discussionon each dusty plasma experiment and data analysis toolsare presented in this paper. However, this paper onlyhighlights opportunities for physics graduate students forperforming some basic experiments in the physics lab us-ing the dusty plasma device which can be operated ei-ther in DC or RF discharge configuration. The mainfocus of this article to highlight only the advantages ofdusty plasma experiments to physics students by citingthe previous experimental studies. A detailed procedure(or tutorial) for an individual experiment could be a fu-ture scope.
X. ACKNOWLEDGEMENT
The author is grateful to Prof. Merlino, Prof. Lin I,Prof. Hyde and Dr. Shaw for allowing him to reuse thepublished figures with permission of publishers. Authoris also thankful to Dr. R. Rajawat, Dr. V. Kella and Dr.A. Gupta for careful reading of this paper. F. F. Chen,
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