Adobe Systems Fyzika plazmatu 2 1 Plasma Physics 2 Adam Obrusník, adamobrusnik@physics.muni.cz Tomáš Hoder, hoder@physics.muni.cz Adobe Systems Fyzika plazmatu 2 2 Lecture series contents 1.Townsend breakdown theory, Paschen‘s law 2.Glow discharge 3.Electric arc at low and high pressures 4.Magnetized low-pressure plasmas and their role in material deposition methods. 5.Brief introduction to high-frequency discharges 6.Streamer breakdown theory, corona discharge, spark discharge 7.Barrier discharges 8.Leader discharge mechanism, ionization and discharges in planetary atmospherres 9.Discharges in liquids, complex and quantum plasmas 10.Thermonuclear fusion, Lawson criterion, magnetic confinement systems, plasma heating and intertial confinement fusion. Adobe Systems Fyzika plazmatu 2 3 Discharges – what this Lesson covers? Adobe Systems Fyzika plazmatu 2 4 Contents of this lesson ̶The diffusivity tensor – why do we magnetize plasma? ̶ ̶Estimating when the magnetic confinement makes sense – numerical assessment and intro to BOLSIG+ ̶ ̶Important applications of magnetized plasmas: ̶Magnetron sputtering PVD and its broad applications. ̶Vacuum arc PVD ̶ECR particle generators ̶Hall thrusters Adobe Systems Fyzika plazmatu 2 5 The diffusivity tensor – why do we magnetize plasma Adobe Systems Fyzika plazmatu 2 6 Why do we magnetize plasma? ̶To control its spatial distribution or to provide ExB acceleration… Filtered vacuum arc Hall thruster for satellites Research | CSU Electric Propulsion & Plasma Engineering (CEPPE) Laboratory at Colorado State University Magnetron Sputtering Deposition – magnetron sputtered thin films Magnetron sputtering plasma (likely a wafer processing setup) Adobe Systems Fyzika plazmatu 2 7 Why do we magnetize plasma? AO’s favourite reference for all the derivations mentioned here is the Liebermann book Adobe Systems Fyzika plazmatu 2 8 Values of diffusion coefficients AO’s favourite reference for all the derivations mentioned here is the Liebermann book Adobe Systems Fyzika plazmatu 2 9 Magnetized diffusion AO’s favourite reference for all the derivations mentioned here is the Liebermann book Hall diffusion (e.g. gradient in X causes diffusion in Y direction) Adobe Systems Fyzika plazmatu 2 10 Magnetized diffusion ̶Magnetic field hinders diffusion of electrons in the direction perpendicular to it => electrons get more confined ̶Due to the plasma space charge, ions get confined as well ̶There is then something like „magnetized ambipolar diffusion“, but it cannot be expressed analytically. AO’s favourite reference for all the derivations mentioned here is the Liebermann book Hall diffusion (e.g. gradient in X causes diffusion in Y direction) Adobe Systems Fyzika plazmatu 2 11 Why do we magnetize plasma? ̶Just by looking at these plasmas, we can sometimes guess the direction of B fields Filtered vacuum arc Hall thruster for satellites Research | CSU Electric Propulsion & Plasma Engineering (CEPPE) Laboratory at Colorado State University Magnetron Sputtering Deposition – magnetron sputtered thin films Magnetron sputtering plasma (likely a wafer processing setup) Adobe Systems Fyzika plazmatu 2 12 Magnetized diffusion - quantifying Adobe Systems Fyzika plazmatu 2 13 Magnetized diffusion - quantifying We learned a few things: ̶With permanent magnets, we can only confine plasma at the low pressures ̶At higher pressures or even atm. pressure, extremely high B field would be required for the confinement, attainable only by coils, ideally superconducting  ̶At high pressures, the high collisionality breaks the confinement ̶On a microscopic level, we can imagine that the gyrating electron undergoes too many collisions during one gyration. ̶ Adobe Systems Fyzika plazmatu 2 14 Applications of magnetized plasma Adobe Systems Fyzika plazmatu 2 15 Applications – magnetron sputtering ̶Magnetron sputtering is a so called PVD (physical vapor deposition) technique for converting solids to gases at the low temperature. ̶On the plasma physics level, it is a magnetized glow discharge. An Overview of Sputtering Deposition | Technological knowledge Adobe Systems Fyzika plazmatu 2 16 Applications – magnetron sputtering ̶On the surface, the the so-called collision cascade can occur, whereby a neutral atom is knocked off the solid phase by an incoming ion at high kinetic energy https://www.youtube.com/watch?v=TyYBIj-A9tY ̶This effect occurs if the ion energy is significantly above the suface binding energy (10-20 eV). ̶The probability of this effect is called the sputtering yield and depends highly on material Sputtering Basics - Plasma Quest Sputtering yield as a function of atomic number of the target. | Download Scientific Diagram Sputter Yield - an overview | ScienceDirect Topics Adobe Systems Fyzika plazmatu 2 17 Applications – magnetron sputtering ̶Why cannot we sputter without B field, e.g. by increasing the pressure? ̶Our primary objective is depositing metal atoms onto the surface. The higher the pressure, the more they will scatter and the larger the material loss. ̶We want to have plasma at as low pressure as possible but still as dense as possible => This is usually the argument for magnetizing plasmas  ̶Magnetic field ensures that the plasma is dense where we want it – at the surface of the sacrificial cathode. An Overview of Sputtering Deposition | Technological knowledge Adobe Systems Fyzika plazmatu 2 18 Applications – low pressure vacuum arc ̶In a vacuum arc PVD, almost an identical B field setup is used but for different reasons! ̶ ̶Also, gas pressure in vacuum arcs is higher, about 1-3 Pa. ̶ ̶The plasma is not a nice and stable glow discharge but a rather stochastic arc discharge. https://www.youtube.com/shorts/rx6uX3g1Ss8 ̶ ̶ PVD Coatings - Fraunhofer IWS Adobe Systems Fyzika plazmatu 2 19 Applications – low pressure vacuum arc Vacuum Arc Cathode Spot Theory: History and Evolution of the Mechanisms | Semantic Scholar The Interaction of the Vacuum Arc and a Transverse Magnetic Field Adobe Systems Fyzika plazmatu 2 20 Application – Hall thrusters ̶One of the most established methods of satellite electric propulsion. ̶Plasma is accelerated through ExB drift and the extracted plasma is quasineutral Schematic drawing of the Hall effect thruster. | Download Scientific Diagram New thrusters for NASA's moon-orbiting Gateway space station get a test | Space Adobe Systems Fyzika plazmatu 2 21 Take aways ̶Why use magnetic field in a plasma? ̶ ̶How to quantify when magnetizing the plasma is going to have some effect? ̶ ̶Applications of magnetized plasma discharges and difference between the magnetic field role in arc PVD and sputter PVD ̶