Kein Folientitel

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Diagnostics of Fusion Plasmas Spectroscopy
Ralph Dux
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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

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Important reactions for ionisation and excitation
balance
Reaction rates product of densities x rate
coefficient (atomic physics)
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Contributions to the plasma radiation
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Energy levels of atoms, ions and molecules
(dimers)
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Energy levels of atoms, ions and molecules
(dimers)
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Radiative transitions between bound states
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Radiative transitions between bound states
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Interference on gratings and crystals
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Types of spectrometers for different wavelength
ranges
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Density of emitting ions from spectroscopy
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Density of emitting ions from spectroscopy
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Corona ionisation balance
In fusion plasmas (and in the solar corona) low
electron densitythree body recombination rate
(?ne2) ltlt radiative recombination rate (?ne)
Balance of
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 Eion13.6eV Z2

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Corona ionisation balanceArgon
ions with filled electron shellsare most stable
(He-like, Ne-like ) He- and H-like
ionsationstages of Ar still present up to the
plasma center
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Corona ionisation balanceTungsten
Th. Pütterich Ph.D. thesis 2005
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Impurity density determinationX-ray spectroscopy
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Impurity density determinationX-ray spectrum of
tungsten
This line from W46 is used for density
evaluation at AUGD.
Th. Pütterich, PhD thesis 2005
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Impurity density determinationtungsten
concentrations
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Impurity influx measurementsVisible Spectroscopy
Neutral impurity atoms(or low ion stages)
radiatesufficiently strong visibleline
emission. ? Can be used to determine the
erosion rates at the plasma walls (impurity
influx)
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Impurity influx measurementsVisible Spectroscopy
1dim continuity equation for neutrals (small
recombination rates ionising plasma)
temporal equilibrium
Integrate up to l, where all neutrals are ionised
x
x0
0
l
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 x0 where the
excitation and ionisation mainly occurs
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Impurity influx measurementsVisible Spectroscopy

• S/XB-value
• number of ionisations per emitted photon
• gives impurity influx from photon flux
• ? independent of ne

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Impurity influx measurementsInflux of tungsten
from the divertor strike point tiles
Strongest W-erosion inthe divertor
(modulationdue to ELMs)
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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

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Natural line width
Oscillation with decay time ??
Spectral emission coefficient
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Doppler shift and Doppler broadening
? measurement of ion temperatureand drift
velocity
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Active Spectroscopy on Hydrogen BeamCharge
Exchange Recombination Spectroscopy
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Active Spectroscopy on Hydrogen BeamCharge
Exchange Recombination Spectroscopy
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Stark broadening (Hydrogen)Linear Stark Effect
In Hydrogen the electric field leadsto 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 n3,4,5,6,7 ? 2)
In the edge plasma Linear Stark broadening dueto
time varying microfields from electrons and ions
candominate Doppler broadening ? measurement of
ne
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Stark broadening (Hydrogen)Linear Stark Effect
In Hydrogen the electric field leadsto a line
splitting linear with the field strength (?
linear Stark effect)
Profile of Balmer-?? lines of Deuterium (n7? 2)
measured in the ASDEX Upgrade divertor
In the edge plasma Linear Stark broadening dueto
time varying microfields from electrons and ions
candominate Doppler broadening ? measurement of
ne
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Active Spectroscopy on Hydrogen BeamMotional
Stark effect polarimetry

• Observe D? spectrum of D0 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 linearStark
  effect

60kV D0 beam, B2T
Polarization ?-components (?m0) parallel to el.
field ?-components (?m1) perpendicular to el.
field
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Active Spectroscopy on Hydrogen BeamMotional
Stark effect polarimetry

• Observe D? spectrum of D0 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 linearStark
  effect

60kV D0 beam, B2T
Polarization ?-components (?m0) parallel to el.
field ?-components (?m1) perpendicular to el.
field
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Active Spectroscopy on Hydrogen BeamMotional
Stark effect polarimetry

• Observe D? spectrum of D0 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 linearStark
  effect

60kV D0 beam, B2T
Polarization ?-components (?m0) parallel to el.
field ?-components (?m1) perpendicular to el.
field
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Active Spectroscopy on Hydrogen BeamMotional
Stark effect polarimetry

• 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)

Additional radial electric field changes
polarization direction
? measurement of 2 beam energy components is
used to separate both contributions
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Line splitting in the magnetic fieldZeeman 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

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Line splitting in the magnetic fieldZeeman Effect
B-field splitting for CII here more emission from
HFS

• 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

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Line splitting in the magnetic fieldZeeman Effect
B-field splitting for CII here more emission from
LFS

• 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

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Line splitting in the magnetic fieldZeeman Effect
B-field splitting for Balmer-? of D dominated by
LFS

• 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