State doctoral exam topics
Plasma Physics
Introduction to plasma physics
- Criteria for the definition of plasma. Plasma frequency, cyclotron frequency, collision frequency, mean free path, Debye length, magnetic pressure, beta parameter.
- Temperature. Saha equation, ranges of temperature and electron density for plasma. General properties of various types of plasma.
- Plasma dielectric constant. Polarization, magnetization. Plasma polarization tensor.
- Motion of charged particles. Equation of motion, adiabatic invariants, drifts. Motion in magnetic dipole and in magnetic mirror.
- Transport equations. Ohm´s, Fick´s and Fourier´s law. Onsager reciprocal relations. Diffusion, mobility, ambipolar diffusion. Diffusion across magnetic field, effect of collisions on diffusion in magnetic field, plasma resistivity.
- Statistical description of plasma. Boltzmann equation, Fokker-Planck equation. Higher moments of the distribution function.
- Collisions in plasmas. Cross sections. Coulombic collisions. Coulomb´s logarithm. Runaway solution. Chandrasekhar's function.
- Foundation of magnetohydrodynamics. Continuity equation, equation of motion, equation for magnetic field. Frozen in and diffusion magnetic field.
- Thermonuclear fusion. Basic reactions. History, presence and future. Lawson criterion. Tokamak and stellarator. Inertial fusion.
- Waves in plasma. Alfvén magnetoacoustic wave complex. Electromagnetic waves in plasma (O, X, R, L wave). CMA diagram.
- Plasma instabilities. Kelvin-Helmholtz, Rayleigh-Taylor instabilities, instabilities of plasma column – sausage, kink, and m > 2 instabilities. Two-stream (Buneman) instability.
- Force free configuration. Helicity, helical structures, conservation of helicity, examples of helical structures, conditions for violation of the helicity conservation law.
Electrical discharges, applications
- General classification of electrical discharges. Self-sustained and non- self-sustained discharge. Current voltage characteristic of discharge at low pressure. Silent discharge, glow discharge and arc.
- Application of electrical discharges. Plasma technologies. Direct and indirect plasma treatment. Applications of discharge products.
- Elementary processes on electrodes and in discharge volume. Thermal emission, secondary emission, cold emission, explosive electron emission, photoemission. Excitation, dissociation and ionization, formation of radicals. Thermal and non-thermal plasma. Afterglow.
- Townsend theory and breakdown voltage. Physics of electron avalanches,description of an avalanche, breakdown, applications. Condition for initiating a self- sustained discharge. Breakdown voltage and engineering estimation of breakdown voltage. Paschen´s law.
- Glow discharge at low pressure. Characteristic regions and physics of glow discharge. Effect of various parameters on glow discharge. Reactions taking part in glow discharge.
- Discharges at atmospheric pressure. Positive, negative and bipolar corona discharge. Trichel pulses. Warburg´s law. Dielectric barrier discharge. Gliding arc. Stabilization and homogenization of discharges at atmospheric pressure.
- High frequency and microwave discharge. Discharge properties. Microwave sources of plasma. Sliding discharges. Applications of microwave plasma.
- Arc discharge and spark. Definition and characteristic features of these discharges, description and applications. Description of lightning discharge and its peculiarities.
- Z-pinch. Bennett equilibrium and plasma pressure formula p(r), Bennett formula for pinch temperature. Reverse pinch. Cylindrical instability modes, Kruskal stability condition. Electromagnetic collapse.
- Self-organization of plasma structures in the discharge. Minimum magnetic energy condition and its relationship to helical structures and self-organization.
Plasma diagnostics and simulations
- Measurements of current, voltage and potential. Methods of measurements. Langmuir probe, Rogowski coil.
- Measurements of magnetic fields. Faraday rotation, Zeeman effect, direct measurement of magnetic fields, magnetometers.
- Foundations of spectroscopy. Optical emission spectroscopy, spectral lines, measurement of temperature, density, rotational and vibrational spectra, plasma constituents and other plasma characteristics. Heat capacity of vibrational and rotational states.
- Visualization diagnostic techniques. Interferometric and schlieren methods for measurements of electron densities and gradients of electron densities.
- Microwave and corpuscular diagnostics.Overview of methods and detecting plasma parameters, neutrons detection.
- Measurement of plasma density. Overview of basic methods, determination of density from propagation of electromagnetic waves, significance of plasma frequency.
- X-ray diagnostics of hot plasma. Mechanism of production of X-ray emission. Detection of X-ray emission. Parameters determinable by X-ray diagnostics.
- Numerical simulation basics. Numerical solution of ordinary and partial differential equations (basic principles). Examples of difference schemes. Convergence and stability of the scheme. Hybrid methods.
- Particle and field solvers. Equation of motion solvers (Boris-Buneman, Leap-frog, Runge-Kutta). Partial differential equation solvers (difference schemes, finite elements, multigrid and FFT solvers).
- Selected numerical methods in plasma physics. Monte Carlo simulations – probability distribution realization, Metropolis method, optimization methods (simulated annealing). Perturbation theory. Series expansion. PIC simulations (basic steps of PIC algorithm).