European Joint PhD Programme, Lisboa, Diagnostics of Fusion Plasmas Spectroscopy Ralph Dux

The Methods Passive Spectroscopy (line averaged) X-ray, soft X-ray  impurity species, impurity densities, ion temperature, velocity Visible (VUV)  impurity species, impurity influx, hydrogen influx, electron density Active Spectroscopy (spatially resolved) Charge exchange recombination spectroscopy  ion temperature, velocity (radial electric field), impurity density of fully ionized species Motional Stark Effect Polarimetry  direction of magnetic field

Important reactions for ionisation and excitation balance Reaction rates: product of densities x rate coefficient (atomic physics)

Contributions to the plasma radiation

Energy levels of atoms, ions and molecules (dimers)

Radiative transitions between bound states

Interference on gratings and crystals

Types of spectrometers for different wavelength ranges

Density of emitting ions from spectroscopy

Corona ionisation balance electron impact ionisation = radiative recombination ionisation degree is independent of electron density charge state of ion increases with electron temperature low-Z impurities are fully ionized in large part of the plasma (  no line emission from light elements) medium to high-Z impurities can be dedected hydrogen like ions: E ion =13.6eV Z 2 In fusion plasmas (and in the solar corona): low electron density three body recombination rate (  n e 2 ) << radiative recombination rate (  n e ) Balance of:

Corona ionisation balance Argon ions with filled electron shells are most stable (He-like, Ne-like …) He- and H-like ionsation stages of Ar still present up to the plasma center

Corona ionisation balance Tungsten Th. Pütterich Ph.D. thesis 2005 ionisation stages of tungsten

Impurity density determination X-ray spectroscopy

Impurity density determination X-ray spectrum of tungsten Th. Pütterich, PhD thesis 2005 This line from W 46+ is used for density evaluation at AUGD.

Impurity density determination tungsten concentrations

Impurity influx measurements Visible Spectroscopy Neutral impurity atoms (or low ion stages) radiate sufficiently strong visible line emission.  Can be used to determine the erosion rates at the plasma walls (impurity influx)

Impurity influx measurements Visible Spectroscopy 1dim continuity equation for neutrals (small recombination rates = ionising plasma) temporal equilibrium: Integrate up to l, where all neutrals are ionised: The photons emitted on transition i  k per area and time: Excitation rate and ionisation rate shall have similar temperature dependence (excitation energy  ionisation energy) around x 0 where the excitation and ionisation mainly occurs: x 0 l x0x0

Impurity influx measurements Visible Spectroscopy S/XB of W I nm 5d 5 ( 6 S) 6s - 5d 5 ( 6 S) 6p 7 S – 7 P° S/XB Te / eV A. Geier et al., Rev. Sci. Instr. (1999) A. Geier et al., Plasma Phys. Control. Fusion (2002) Steinbrink et al., 24th EPS 1997 Tw= 0.3 eV Tw= 1 eV calculations: I Beigman et al., Plasma Phys. Control. Fusion (2007) S/XB-value: number of ionisations per emitted photon gives impurity influx from photon flux  independent of n e

Impurity influx measurements Influx of tungsten from the divertor strike point tiles Strongest W-erosion in the divertor (modulation due to ELMs)

Beyond impurity densities and fluxes spectroscopy can also deliver information about temperatures electron density B-field from the line shape or the splitting of spectral lines

Natural line width Oscillation with decay time  Spectral emission coefficient:

Doppler shift and Doppler broadening  measurement of ion temperature and drift velocity

Active Spectroscopy on Hydrogen Beam Charge Exchange Recombination Spectroscopy

Stark broadening (Hydrogen) Linear Stark Effect In the edge plasma Linear Stark broadening due to time varying microfields from electrons and ions can dominate Doppler broadening  measurement of n e In Hydrogen the electric field leads to a line splitting linear with the field strength (  linear Stark effect) Line splitting of the Balmer lines of Hydrogen (Balmer= transitions between states with principal quantum number n=3,4,5,6,7  2)

Stark broadening (Hydrogen) Linear Stark Effect In the edge plasma Linear Stark broadening due to time varying microfields from electrons and ions can dominate Doppler broadening  measurement of n e In Hydrogen the electric field leads to a line splitting linear with the field strength (  linear Stark effect) Profile of Balmer-  lines of Deuterium (n=7  2) measured in the ASDEX Upgrade divertor

Polarization  -components (  m=0): parallel to el. field  -components (  m=±1): perpendicular to el. field Observe D  spectrum of D 0 beam wavelength shifted due to Doppler effect electric field in reference frame of D-atoms due to movement in magnetic field leads to splitting of energy levels via the linear Stark effect: Active Spectroscopy on Hydrogen Beam Motional Stark effect polarimetry D 0 (60keV) Lines-of-sight 60kV D 0 beam, B=2T:

Polarization  -components (  m=0): parallel to el. field  -components (  m=±1): perpendicular to el. field Observe D  spectrum of D 0 beam Wavelength shifted due to Doppler effect electric field in reference frame of D-atoms due to movement in magnetic field leads to splitting of energy levels via the linear Stark effect: Active Spectroscopy on Hydrogen Beam Motional Stark effect polarimetry D 0 (60keV) Lines-of-sight 60kV D 0 beam, B=2T:

Polarization  -components (  m=0): parallel to el. field  -components (  m=±1): perpendicular to el. field Observe D  spectrum of D 0 beam Wavelength shifted due to Doppler effect electric field in reference frame of D-atoms due to movement in magn. field leads to splitting of energy levels via the linear Stark effect: Active Spectroscopy on Hydrogen Beam Motional Stark effect polarimetry 60kV D 0 beam, B=2T:

unshifted  -component is selected with very narrow interference filter (just works for one beam voltage) polarization direction of light is determined (accuracy  1/10 degree) Active Spectroscopy on Hydrogen Beam Motional Stark effect polarimetry Additional radial electric field changes polarization direction:  measurement of 2 beam energy components is used to separate both contributions

Line splitting in the magnetic field Zeeman Effect Level splitting: Zeeman case: angular momentum of orbit and spin remain coupled in ext. B-field  measurement of B? No! but can be used to get the main emission region on the LOS

Line splitting in the magnetic field Zeeman Effect Level splitting: Zeeman case: angular momentum of orbit and spin remain coupled in ext. B-field B-field splitting for CII here more emission from HFS  measurement of B? No! but can be used to get the main emission region on the LOS

Line splitting in the magnetic field Zeeman Effect Level splitting: Zeeman case: angular momentum of orbit and spin remain coupled in ext. B-field B-field splitting for CII here more emission from LFS  measurement of B? No! but can be used to get the main emission region on the LOS

Line splitting in the magnetic field Zeeman Effect Level splitting: Zeeman case: angular momentum of orbit and spin remain coupled in ext. B-field B-field splitting for Balmer-  of D dominated by LFS  measurement of B? No! but can be used to get the main emission region on the LOS