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Kein Folientitel

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Title: Kein Folientitel


1
Diagnostics of Fusion Plasmas Spectroscopy
Ralph Dux
2
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

3
Important reactions for ionisation and excitation
balance
Reaction rates product of densities x rate
coefficient (atomic physics)
4
Contributions to the plasma radiation
5
Energy levels of atoms, ions and molecules
(dimers)
6
Energy levels of atoms, ions and molecules
(dimers)
7
Radiative transitions between bound states
8
Radiative transitions between bound states
9
Interference on gratings and crystals
10
Types of spectrometers for different wavelength
ranges
11
Density of emitting ions from spectroscopy
12
Density of emitting ions from spectroscopy
13
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

14
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
15
Corona ionisation balanceTungsten
Th. Pütterich Ph.D. thesis 2005
16
Impurity density determinationX-ray spectroscopy
17
Impurity density determinationX-ray spectrum of
tungsten
This line from W46 is used for density
evaluation at AUGD.
Th. Pütterich, PhD thesis 2005
18
Impurity density determinationtungsten
concentrations
19
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)
20
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
21
Impurity influx measurementsVisible Spectroscopy
  • S/XB-value
  • number of ionisations per emitted photon
  • gives impurity influx from photon flux
  • ? independent of ne

22
Impurity influx measurementsInflux of tungsten
from the divertor strike point tiles
Strongest W-erosion inthe divertor
(modulationdue to ELMs)
23
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

24
Natural line width
Oscillation with decay time ??
Spectral emission coefficient
25
Doppler shift and Doppler broadening
? measurement of ion temperatureand drift
velocity
26
Active Spectroscopy on Hydrogen BeamCharge
Exchange Recombination Spectroscopy
27
Active Spectroscopy on Hydrogen BeamCharge
Exchange Recombination Spectroscopy
28
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
29
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
30
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
31
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
32
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
33
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
34
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

35
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

36
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

37
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
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