Modelling ling of Plasma in Electric Propulsion Seminar Report submitted by Name: Reg. Number: Course code: Semester/Batch: Mentor: Deeksha Rao 17ETAS012007 ASC406A 7/2017 Dr. Mahesh K Varpe B. Tech in Aerospace Engineering Department of Aerospace Engineering Ramaiah University of Applied Sciences University House, Gnanagangothri Campus, New BEL Road, M S R Nagar, Bangalore, Karnataka, India - 560 054 Declaration Sheet Student Name Deeksha Rao Reg. No 17ETAS012007 Programme B. Tech. (Aerospace Engineering) Course Code ASC406A Course Title Seminar Course Date 10th September 2020 to Batch 2017 5st March 2021 Declaration The seminar report submitted herewith is a result of my own investigations and that I have conformed to the guidelines against plagiarism as laid out in the Student Handbook. All sections of the text and results, which have been obtained from other sources, are fully referenced. I understand that cheating and plagiarism constitute a breach of University regulations and will be dealt with accordingly. Signature of the Date student Name Signature Date First Examiner Second Examiner Mentor MEC406A-Seminar i Contents Declaration Sheet..................................................................................................................... i LIST OF TABLES ........................................................................................................................ v LIST OF FIGURES ...................................................................................................................... v ABSTRACT ................................................................................................................................ 1 1 Introduction and scope of work ..................................................................................... 2 1.1 Introduction: ......................................................................................................... 2 1.2 Motivation: ............................................................................................................ 2 1.3 Definition of Important terms ............................................................................... 3 2 Literature Review ........................................................................................................... 4 2.1 Working of Hall Thruster ....................................................................................... 4 2.2 Different Models of Plasma .................................................................................. 4 2.2.1 Kinetic Model ................................................................................................. 5 2.2.2 Fluid Model .................................................................................................... 5 2.2.3 Hybrid Model ................................................................................................. 6 2.3 3 Design Implications ............................................................................................... 7 Details of the Topic ........................................................................................................ 8 3.1 History ................................................................................................................... 8 3.2 Implications ........................................................................................................... 8 3.3 Working of the Hall Thruster................................................................................. 8 3.4 Different Models of Plasma .................................................................................. 9 3.4.1 Kinetic Model ............................................................................................... 10 3.4.2 Fluid Model .................................................................................................. 11 3.4.3 Hybrid Model ............................................................................................... 12 3.5 Design of Hall thruster ........................................................................................ 12 3.6 Facts and Figures ................................................................................................. 14 3.7 Data Analysis ....................................................................................................... 14 MEC406A-Seminar ii 3.8 4 Results ................................................................................................................. 16 Challenges and Opportunities ...................................................................................... 16 4.1 Challenges ........................................................................................................... 16 4.2 Opportunities ...................................................................................................... 16 5 Conclusion and Suggestions for Future Work .............................................................. 18 5.1 Conclusion ........................................................................................................... 18 5.2 Future Work ........................................................................................................ 18 6 REFERENCES ................................................................................................................. 19 MEC406A-Seminar iii LIST OF ABBREVIATIONS AND NOMENCLATURE 1D 1 Dimensional 2D 2 Dimensional 3D 3 Dimensional PIC Particle in Cell MCC Monte Carlo Collision SEE Secondary Electron Emission MHD Magneto-hydrodynamic HET Hall effect thruster MEC406A-Seminar iv LIST OF TABLES Table 2-1 .............................................................................................................................. 4 Table 2-2 .............................................................................................................................. 4 Table 2-3 .............................................................................................................................. 5 Table 2-4 .............................................................................................................................. 5 Table 2-5 .............................................................................................................................. 6 Table 2-6 .............................................................................................................................. 7 Table 3-1 Comparison of data............................................................................................ 14 LIST OF FIGURES Figure 1-1 Plasma................................................................................................................. 2 Figure 1-2 Hall thruster and Plasma modeling .................................................................... 3 Figure 3-1 Schematic Representation of Hall thruster ........................................................ 9 Figure 3-2 Flow chart representing explicit PIC cycle(3) ................................................... 10 Figure 3-3 Coupling of the Fluid solver and electro-dynamic solver (4) ........................... 11 Figure 3-4 Iterative Design process for Hall Thrusters (6) ................................................. 12 Figure 3-5 SPT 100 ............................................................................................................. 14 Figure 3-6 Comparison of Electric Field predicted by authors(7,8) ................................... 15 Figure 3-7 Comparison of Number Density predicted by authors .................................... 15 Figure 3-8 Comparison of Normalized Magnetic Field ...................................................... 15 MEC406A-Seminar v ABSTRACT This paper presents an overview of the recent advances made in the field of plasma modeling in reference to the electric propulsion. Hall thrusters are an advanced plasmapropelled electric propulsion device. Modeling of the plasma discharges in Hall thrusters are gaining traction in the Engineering Field, as the design of Hall thrusters require the modeling of the Plasma. Thus, it has become important for the Engineering Community to understand plasma dynamics involved in the construction and analysis of the Hall thruster. The main objective is to provide engineers with a comprehensive guide which can help choose the best model for a given parameters and conditions. Numerical models have disclosed several physical mechanisms, present in the functioning of the Hall Thruster. It acts as a bridge between the analytical and experimental studies. There are 3 different approaches that exist for the creation of numerical model: a kinetic model which uses kinetic description of the particles at a microscopic level and are described using particle velocities; a Fluid model which uses macroscopic quantities such as density, energy and velocity, and assumes plasma to be quasi-neutral and collision less and is set in a macroscopic level; a Hybrid model which uses best features of both the models, it also leads to computational efficiency. Fluid and Hybrid models are quantified for performance parameters and validated against the measured values. The fluid model yields least error in the performance parameters. This model is used in design of Hall thruster. Keywords: Hall Thruster, Plasma Modeling, Kinetic Model, Fluid, Hybrid approach ASC406A-Seminar 1 1 1.1 Introduction and scope of work Introduction: Plasma, the fifth state of matter is one of the wonderful states which is has many uses ranging from electric propulsion to tokomak reactor to Welding. This versatile state of matter is also found in stars. Plasma refers to a soup of positive ions, neutrals and electrons, which is quasi-neutral in nature. Figure 1-1 Plasma Modelling this state of matter is multi-physics affair. Modelling of plasma helps us to mathematically characterize several applications and helps improve performance of the application. A few applications of Plasma are: Fusion reactor, Electric propulsion and plasma welding. Electric Propulsion is the future of propulsion. Plasma modelling is an integral part of Ion and Hall thrusters 1.2 Motivation: Electric propulsion is one of the most sought-after technologies in the Space realm. There are several types of electric propulsion systems. Ion thrusters, Hall thrusters and MPD thrusters usually use plasma as a means of producing thrust. Plasma propulsion systems lead to greater exhaust speeds. Hall thrusters are very efficient and competitive electric propulsion devices for satellites and are currently in used in a number of telecommunications and government spacecraft. Thus, there is a demand for plasma modeling and analysis. ASC406A-Seminar 2 Figure 1-2 Hall thruster and Plasma modeling There is a plethora of engineering applications which require plasma modeling. Thus, looking into the wide array of plasma modeling techniques from an Engineering perspective is the main motivation for conducting this study. 1.3 Definition of Important terms Debye length: It is a characteristic length over which ions and electrons can be separated in a plasma It represents the physical scale of the transition from plasma continuity to individual particle behaviour. Larmour Radius: This is the radius of circular motion and charged particle in presence of a uniform magnetic Field Quasi-neutrality: It refers to the state of plasma, that at macroscopic level is neutral(i.e., density of ions = density of electrons) Cold Plasma: It refers to the plasma, where ions and neutrals are in a much lower temperature, when compared to electron temperature 1.4. Issues Plasmas in electric propulsion devices, even in individual parts of a thruster, can span orders of magnitude in plasma density, temperature, and ionization fraction. Therefore, models used to describe the plasma behavior and characteristics in the thrusters must be formed with assumptions that are valid in the regime being studied. ASC406A-Seminar 3 2 2.1 Literature Review Working of Hall Thruster Table 2-1 Sl Paper Model Type Salient Feature Reference no. 1 D.M. Goebel, I. Katz, Single particle (2008), Fundamentals of Model, Fluid electric propulsion: Hall Model Basics, 2 J.P. thrusters Boeuf, and and Hall thrusters parameters Cathodes Plume modelling Classic transport Hall thrusters, Journal of Various mechanism 121, mechanisms 011101 and electron Kinetic, Fluid and present in Hall Hybrid Thruster, Basics Case [1] Basic Performance Hollow Tutorial: Physics of Hall Physics, of the Basics of Ion Physics and modeling of Thruster, Applied deep understanding and ion thrusters Wiley, Working of Hall Hoboken A [2] Model studies 2.2 Different Models of Plasma Table 2-2 Sl no Paper 1 Model type Tang, Haibin and York, Concepts Thomas M. Salient Features in (2015), Plasma physics, Numerical models of different techniques Introduction to Plasmas sheaths, Applications and Case studies With Plasma Reviews Applications Propulsion, ASC406A-Seminar Dynamics. collisions in Reference [3] of Space Magnetic 4 Fusion and Space Physics , Academic Press 2 Gianpiero Colonna, Kinetic Models, Antonio D’Angola, Plasma Fluid Models Modeling Methods and and Hybrid Applications, IOP Plasma approach Numerical techniques for [4] various models Stability analysis Physics Series 2.2.1 Kinetic Model Table 2-3 Sl no Paper Model type 1 Domínguez-Vázquez, A., Taccogna, F. y Ahedo, E. (2018). Particle modeling of radial electron dynamics in a controlled discharge of a Hall thruster. Plasma Sources Science and Technology, 27(6) 1D(z) PIC MCC Salient Features Reference Particle Model used Model in radial section of Hall thruster in acceleration region Secondary [5] electron emmission 2.2.2 Fluid Model Table 2-4 Sl Paper Model type Salient features Reference no. 1 Kwon Kybeom, Walker 1D Fluid, Self- Mitchell L R, and Mavris consistent Dimitri N, (2011), Selfconsistent, one- dimensional analysis of the Hall effect thruster, Plasma ASC406A-Seminar Sources Sci. 1D, Self sufficient, Macroscopic A collisionless electron diffusion region A collisional dominant [7] electron diffusion region. 5 Technol. 20 045021 2 Manzell David, (), 1D Fluid Simplified Numerical Description of SPT Simplified Model Easy implementation [11] Operation, IEPC-95-34 2.2.3 Hybrid Model Table 2-5 Sl no Paper 1 K. Model type Hara, Kolobov D. Boyd, Vladimir, and 1D Salient Features Hybrid Improved performance (2011), Vlasov Hybrid-Vlasov Simulation For [8] Hall Thrusters, 2nd Annual Graduate Reference Student Symposium, (Ann Arbor, MI) 2 Mikellides I G, Katz I, Mandell 1D Hybrid 1-D computer model M J, and Snyder J S (2001), A has been developed in 1-D Model of the Hall-effect the interest of thruster with an Exhaust investigating plasma Region, behavior in the Proc. 7th AIAA/ASME/SAE/ASEE Joint acceleration channel Propulsion Conf. (Salt Lake and region City, UT) (Washington, DC: downstream of the American Hall-Effect Thruster Institute Aeronautics of [9] and Astronautics) AIAA-2001- 3505 3 Boeuf, J. P. and Garrigues, 1D Hybrid-PCC Quasi-neutral plasma L.,(1998), column, Low frequency oscillations in a stationary ASC406A-Seminar [10] Electron energy with 6 plasma thruster, Journal of Applied Physics, vol. no temporal evolution 84, 3541-3554 2.3 Design Implications Table 2-6 Sl no Paper 1 Model type Enrico A. De Marco and 2D Salient features Reference magnetic Optimization of Design Mariano Andrenucci (2008), Circuit, 1D Hall Thrusters Design and Plasma Model Optimization, 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference [6] & Exhibit (Hartford, CT), AIAA 2008-4805 ASC406A-Seminar 7 3 3.1 Details of the Topic History The Hall thrusters have been in development fro over last 50 years, making it a recent advancement. Plasma modeling started with gusto in the late 1990s, starting with onedimensional models along the axial direction. Along with that, some of the one-dimensional models along the radial direction have been used to simulate the effect of SEE under the impact of high-energy electrons on ceramic walls of the channel on plasma properties. Twodimensional models that account for axial and radial directions often channel and near-field regions have been developed since the early 2000s to better capture plasma properties and expansion. More recently, a two-dimensional model along the axial and azimuthal directions has been proposed (5). Recent advances in this field have lead to the development of sophisticated tools which has made plasma modelling more user-friendly. Advent of commercial codes like ANSYS Maxwell and COMSOL Multiphysics, in the field of plasma modelling has made it easier and more graphic for the easy understanding of the field. 3.2 Implications Hall thrusters have good Specific Impulse. This leads to less consumption of propellant and it have very good life time. There no indigenously built hall thruster in India. Thus, in business point of view, there is market for Hall thrusters in India without any competitors. Since, Hall thrusters use electricity and Xenon to produce thrust. There are no harmful Pollutants during emission. Thus, it is eco-friendly. 3.3 Working of the Hall Thruster Geometry of the Hall thrusters has been shown in the above figure. It consists of 1 cylindrical channel with n electromagnet in the middle and 4 more electromagnets at the corner of the thrusters. There is anode plate at one of the thrusters and Hollow cathode perched on top of the other edge of the Hall thrusters. The insides of the channel are coated with dielectric materials, usually Boron nitride. Nobel Gases are usually used a propellants. Xenon is the most preferred propellant for the Hall Thruster (1). ASC406A-Seminar 8 Figure 3-1 Schematic Representation of Hall thruster Hall thrusters are electromagnetic thrusters, which propels, using the Lorentz Force and the Hall Effect. Magnetic Field is applied in radial direction, whereas Electric field is applied in axial direction. The electric and Magnetic field is applied perpendicular to each other. Neutral Xenon gas is sent through injector into the channel. On application of the electric field, plasma is generated. The electrons emitted from the Cathode ionize the gas. The continually applied Electric field lowers the electron conductivity (2). The electrons are confined by the magnetic field, whereas the Ions are accelerated to produce the Thrust. The Ion beam is then neutralized by the Hollow Cathode present on the Outer edge of Hall Thruster. 3.4 Different Models of Plasma There are 3 different types of plasma modelling techniques: 1. Kinetic Model ASC406A-Seminar 9 2. Fluid Model 3. Hybrid Model 3.4.1 Kinetic Model Kinetic Model has 2 different models: 1. Particle models 2. Boltzmann Vlasov equations Particle Models model the single particle motion of one species and then uses those equations to model the species as the sum of th the individual particle motion. For this to be used in a Hall thruster, an electron motion is modelled in electric and Magnetic field. And then it is extrapolated to include the whole species. This is considered as Particle in Cell model. It uses Maxwell’s equations and Newtonian physics in equal measure. Numerical model used for this method is called a leapfrog algorithm. Values of Current density and charge density are aassumed ssumed and then uses Maxwell’s equations to compute electric and magnetic fields at next half time step. In the other half of time step, the obtained fields are used to calculate position and velocity vectors. Thus, the cycle continues, until desired results are achieved. Figure 3-2 Flow chart representing explicit PIC cycle(3) ASC406A-Seminar 10 Boltzmann Valsov system has 7 dimensions system to be calculated. They are probabilistic in nature. The Boltzmann’s equation can be used in conjunction with Maxwell’s equations to get distributions of particles and distribution of properties along axis. 3.4.2 Fluid Model Fluid models consider the plasma as a continuum. There is no need to resolve Debye length in Fluid modelling as Fluid Models are of 2 types: 1. Single Fluid Model 2. Two fluid Model Single fluid model assumes plasma to be a single fluid and uses Navier-Stokes equations. Densities are replaced by plasma number density. Mass fluxes are replaced by electric and Magnetic fluxes. Thus, we need 2 different solvers. This is MHD Formulation. Figure 3-3 Coupling of the Fluid solver and electro-dynamic solver (4) Fluxes are assumed and then fed to the Fluid dynamic solver, this solver gives, velocity, pressure, temperature and number density as output. This ouput serves as input for the electrodynamic solver. This cycle continues until desired result is achieved. Plasma consists of electrons, Ions and neutrals. Two fluid model considers electrons as a one fluid and Ions as another; but this doesn’t change the dimensionality of the model. ASC406A-Seminar 11 3.4.3 Hybrid Model The hybrid approach is the used to bridge the gap between Kinetic and Fluid approach. The Ions are modelled using the Kinetic approach. Electrons are modelled using the fluid approach This helps with chemical reaction in the Hall thruster. This is computationally better than the Kinetic Models and Gives better accuracy than the Fluid approach 3.5 Design of Hall thruster Figure 3-4 Iterative Design process for Hall Thrusters (6) Hall thruster has a few conditions which need to be fulfilled for selecting the length of the channel in a HET. Load initial profiles for the neutral density, neutral velocity, plasma density and ion velocity. Calculate initial estimation of the electron temperature profile. ASC406A-Seminar 12 Solve the neutral and ion equations from the anode (with fixed electron temperature profile). Solve for the discharge current by imposing the potential fall from the anode to the exit. Solve the electron temperature equation from the exit to the anode. Compare the electron temperature distribution since convergence. ASC406A-Seminar 13 3.6 Facts and Figures Figure 3-5 SPT 100 Thruster operating Conditions: Mass flow rate: 5.2 kg/s Inlet neutral Velocity: 175 m/s Discharge Voltage: 300 V Discharge Current: 4.5 A Maximum Magnetic Field:200 G 3.7 Data Analysis Table 3-1 Comparison of data The performance Data of SPT 100 was taken from several different papers to quantify the Measured Data(11) Variable Discharge Current Thrust efficiency Thrust Specific Impulse Breathing mode frequency Unit Id ηt T Isp A mN s 4.50 0.50 83.00 1600.00 w kHz 17.00 Self Consistent(7) Error (in Value %) 4.76 0.49 82.00 1728.00 5.78 2.00 1.20 8.00 1D Hybrid-Vlasov(8) Error (in Value %) Hybrid PIC(9) Error (in Value %) 3.94 0.55 78.90 1547.00 12.44 10.00 4.94 3.31 3.76 0.53 79.00 1548.00 16.44 6.00 4.82 3.25 18.00 5.88 20.00 17.65 Hybrid(10) Error (in Value %) 3.70 0.60 90.20 1500.00 Model ASC406A-Seminar 14 17.78 20.00 8.67 6.25 Electric field V/m Electric field 50000 45000 40000 35000 30000 25000 20000 15000 10000 5000 0 -5000 0 Hybrid Model Fluid Model 0.02 0.04 0.06 Axial Distance m Figure 3-6 Comparison of Electric Field predicted by authors(7,8) Plasma Densities Plasma/Ion Number density 14 12 10 8 6 4 2 0 Hybrid Model Fluid Model 0 0.02 0.04 0.06 Axial Position Figure 3-7 Comparison of Number Density predicted by authors Normalized Magentic Field Variation of Magnetic Field 1.2 1 0.8 0.6 Hybrid Model 0.4 Fluid 0.2 0 0 0.5 1 1.5 x/l Figure 3-8 Comparison of Normalized Magnetic Field ASC406A-Seminar 15 3.8 Results Both Electric and Magnetic Fields are at a maximum at the acceleration zones. High Magnetic fields are required for the confinement of the electrons Fluid model shows high density at the start of acceleration zone when compared to the hybrid model as Fluid considers whole of the Plasma and hybrid considers electrons and Ions separately 4 4.1 Challenges and Opportunities Challenges - Modelling of Plasma Physics Boltzmann equation is made with a system of 7 dimensions. This shows the complexity in the field of Plasma physics. Modelling these equations in conjunction with the Maxwell’s equations involves a lot of hard work and mathematics - Requirement of High Computational Resources In a kinetic model to obtain good results, particle of the order 1011 is required. But most studies use particles of the order 108. This type of study involves a lot of computational resources. - Limited Experimental Data Experimental data available is very limited as building a Hall thruster very expensive and requires lot of theoretical work. 4.2 Opportunities - Enhance predictive capabilities of modelling There have not been many advances in this field. Thus, there are a lot of new avenues to explore in this theoretical sense of plasma physics - Advent of high computational power, may aid in complex Plasma modelling Now the computational Power is increasing exponentially, thus simulations can run for more iterations in less time. And complex modelling techniques also can be now used. - Surge in Plasma-related applications. ASC406A-Seminar 16 The Plasma related applications are now increasing rapidly. New technologies, like plasma gun, Plasma stealth sheath for Military aircrafts are gaining momentum. Thus, increasing the importance of plasma modeling. ASC406A-Seminar 17 5 5.1 1 Conclusion and Suggestions for Future Work Conclusion Research is conducted using 1D Models so that the models can be understood at an preliminary level 2 The data obtained from several papers show that 1D Models are also capable of providing accurate results necessary for the Design Process (6) 3 Kinetic are accurate, but computationally expensive. Kinetic Solvers are required if we need to quantify all the mechanisms in the Plasma thruster. Due to unavailability of data in the field of Kinetic modelling, the performance parameters couldn’t be compared to available data from Fluid and Hybrid Solvers. However, 2D Kinetic Data is available. 4 Fluid/Hybrid Solvers are used by Engineers for getting performance parameters 5 Fluid Models can be used with add-ons to accurately predict performance parameters. Fluid Models accurately predict performance parameters compared to Hybrid Model. Fluid Models are the computationally least expensive, but they cannot capture micromechanisms of Plasma 6 While Fluid/Hybrid models have readily available solvers, Kinetic solvers are not that accessible 5.2 Future Work In an Ideal situation, all the models mentioned, needs to be evaluated under the similar computational domain and initial conditions, so that it can be compared fairly. This overview can be coded using MATLAB Codes to obtain better solution and comparison. There are comparatively less studies undertaken in the 1D Kinetic methods of the Plasma modelling of Hall thrusters, pertaining to its performance. A study can be carried out to obtain performance parameters from 1D Kinetic equation for Plasma modelling in Hall thrusters and its performance. There is less research in the area of Hall thruster design and optimization, Research can be conducted in this field as well. ASC406A-Seminar 18 6 REFERENCES [1] Goebel, D.M. and I. Katz, (2008), Fundamentals of electric propulsion: Hall and ion thrusters Wiley, Hoboken [2] J.P. Boeuf, Tutorial: Physics and modeling of Hall thrusters, Journal of Applied Physics, 121, 011101 [3] Tang, Haibin and York, Thomas M. (2015), Introduction to Plasmas and Plasma Dynamics. With Reviews of Applications in Space Propulsion, Magnetic Fusion and Space Physics, Academic Press [4] Gianpiero Colonna, Antonio D’Angola, Plasma Modeling Methods and Applications, IOP Plasma Physics Series [5] Taccogna, F., Garrigues, L., (2019), Latest progress in Hall thrusters plasma modelling. Rev. Mod. Plasma Phys. 3, 12 https://doi.org/10.1007/s41614-019-0033-1 [6] Enrico A. De Marco and Mariano Andrenucci (2008), Hall Thrusters Design and Optimization, 44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit (Hartford, CT), AIAA 2008-4805 [7] Kwon Kybeom, Walker Mitchell L R, and Mavris Dimitri N, (2011), Self-consistent, one-dimensional analysis of the Hall effect thruster, Plasma Sources Sci. Technol. 20 045021 [8] K. Hara, D. Boyd, and Kolobov Vladimir, (2011), Hybrid-Vlasov Simulation For Hall Thrusters, 2nd Annual Graduate Student Symposium, (Ann Arbor, MI) [9] Mikellides I G, Katz I, Mandell M J, and Snyder J S (2001), A 1-D Model of the Halleffect thruster with an Exhaust Region, Proc. 7th AIAA/ASME/SAE/ASEE Joint Propulsion Conf. (Salt Lake City, UT) (Washington, DC: American Institute of Aeronautics and Astronautics) AIAA-2001-3505\ [10] Boeuf, J. P. and Garrigues, L.,(1998), Low frequency oscillations in a stationary plasma thruster, Journal of Applied Physics, vol. 84, 3541-3554 [11] Manzell David, , Simplified Numerical Description of SPT Operation, IEPC-95-34 ASC406A-Seminar 19