Tokamak Physics Jan Mlyn 5 Electromagnetic radiation from

Tokamak Physics Jan Mlynář 5. Electromagnetic radiation from tokamaks Introduction, EM waves, cyclotron radiation, bremsstrahlung, power losses, atomic processes, excitation, ionisation and recombination, coronal equilibrium, impurity radiation, plasma regions, gamma radiation Fyzika tokamaků 1: Úvod, opakování

Introduction Electromagnetic radiation from tokamak plasmas in practice, EM waves cover a very broad energy spectrum Three (or four) major groups of EM radiation depending on its origin: • collective EM radiation - plasma waves - turbulences, instabilities • radiation of individual plasma particles - cyclotron radiation - bremsstrahlung - ionisation, recombination - excitation, deexcitation • radiation due to nuclear reactions • radiation due to interaction of fast particles with the vessel Tokamak Physics 5: Electromagnetic radiation

Introduction refractive index high-energy photons Size of experimental facility ~ meters Lower frequencies electrostatic or magnetostatic phenomena Tokamak Physics 5: Electromagnetic radiation

Dispersion in plasmas linearised: Kronecker d Tokamak Physics Ohm’s law 5: Electromagnetic radiation

Cyclotron radiation !! cyclotron radiation is not a function of (electrons) n = 1, 2, 3 …. Harmonics due to circular orbit & relativistic effects non-zero line width due to Tokamak Physics • • imperfect field collisional broadening plasma interactions relativistic effects 5: Electromagnetic radiation

Cyclotron radiation Tokamak Physics 5: Electromagnetic radiation

Cyclotron radiation POWER LOSSES due to acceleration in an electric field electric dipole momentum cyclotron radiation: losses increase with velocity v electron losses >> ion losses plasma: Tokamak Physics 5: Electromagnetic radiation

Cyclotron radiation for thermonuclear parameters BUT for n ~ 10 GHz plasma is optically thick, strong re-absorption real power loss negligible & mainly on higher harmonics Tokamak Physics 5: Electromagnetic radiation

Bremsstrahlung is the main radiation loss channel if H plasma is clean (in reality, line & recombination is worse) time duration of a collision energy loss due to bremsstrahlung Tokamak Physics 5: Electromagnetic radiation

Bremsstrahlung Maxwellian Tokamak Physics Kronecker d for cold ions 5: Electromagnetic radiation

Bremsstrahlung, Cherenkov radiation Bremsstrahlung spectrum & suprathermal particles are important ! Cherenkov radiation: Relativistic particles in Tokamak Physics 5: Electromagnetic radiation

Atomic processes General equilibrium condition Tokamak plasma: NOT in a global thermal equilibrium, plasma is transparent to radiation Figure: Example of a recombination spectrum Tokamak Physics 5: Electromagnetic radiation

Atomic processes I) Radiative • bound – bound ~ line spectrum • free – bound : recombination, photoionisation • free – free: ~ bremsstrahlung II) Collisional • electron impact excitation / deexcitation • impact ionisation / 3 -body recombination • autoionisation / dielectronic recombination Tokamak Physics 5: Electromagnetic radiation

Atomic processes in a plasma Tokamak Physics 5: Electromagnetic radiation

Coronal equilibrium • only spontaneous radiative emission • only collisional excitation & ionisation sources [ s-1 ] sinks [ s-1 ] • only collisional ionisation & recombination ionisation states: ionisation recombination Tokamak Physics 5: Electromagnetic radiation

Ionisation and recombination Tokamak Physics 5: Electromagnetic radiation

Ionisation states Tokamak Physics 5: Electromagnetic radiation

Ionisation states Tokamak Physics 5: Electromagnetic radiation

Impurity radiation Line excitation rate averaged over the Maxwellian Recombination: tabulated Impurities cause increased bremsstrahlung, and – even worse – recombination & line radiation. Tokamak plasmas may help to determine s 1 i Tokamak Physics 5: Electromagnetic radiation

Power losses, ionisation states Tokamak Physics 5: Electromagnetic radiation

Limitations of the coronal model • some processes, e. g. autoionisation, prove important • particle transport – diffusion of ion states into the centre There are limits of diagnostics – in particular, resolution line broadening & line shifts due to Doppler effect ~ Ti ~ vq , vf Line splitting & polarisation due to B & E Zeeman effect Tokamak Physics Stark effect 5: Electromagnetic radiation

Limitations of the coronal model Molybden: Carbon cooling rate: LI, 10 -6 e. V cm 3 s-1 Tokamak Physics 5: Electromagnetic radiation

Visible radiation Plasma edge – visible radiation Region without line emission only bremmstrahlung measure of Zeff Tokamak Physics 5: Electromagnetic radiation

UV and XUV spectra Intermediate region – UV, XUV Tokamak Physics ~ 100 e. V 5: Electromagnetic radiation

SXR radiation Plasma core – SXR ~ ke. V Tungsten All lines are emitted by tungsten, by Ge-like, Zn-like, Ni-like etc. ionisation states Tokamak Physics 5: Electromagnetic radiation

SXR from the plasma core Mo line + suprathermal particles Tokamak Physics 5: Electromagnetic radiation

Radiative cooling !! In a good thermonuclear plasma, radiation losses are low compared to the heat & particle transport !! Radiation losses can be substantial at the edge – GOOD, helps to make the wall power load homogeneous ! Poloidal direction LCFS SOL Radiating edge q. SOL qrad qheat rad Tmax Tokamak Physics 5: Electromagnetic radiation

Gamma radiation g photon is a product of a nuclear process (deexcitation of a nucleus) In tokamak plasmas, gs result form nuclear reactions on impurities (see the table in the next slide) ! NOTICE: Lots of X-rays and gs originate in the wall due to fast particles. Tokamak Physics 5: Electromagnetic radiation

Gamma radiation Tokamak Physics 5: Electromagnetic radiation

Tokamak Physics 5: Electromagnetic radiation

Tokamak Physics 5: Electromagnetic radiation