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Roger Jaspers 1

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How to take measurements in a plasma at 150 million C. Roger ... magnetics. fusion product diagnostics. hard x-ray spectroscopy. atomic beam diagnostics ... – PowerPoint PPT presentation

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Title: Roger Jaspers 1


1
How to take measurements in a plasma at 150
million C
  • Roger Jaspers

2
A typical tokamak plasma
  • Parameters Fusion reactor
  • TeTi 150 MK
  • ne1020 m-3
  • Bt 5 T
  • Ip15 MA
  • high neutron flux
  • ? gt 1016 n/m2s

3
Questions
  • What do we want to measure ?
  • Why do we want to measure this ?
  • How are we going to do this?
  • What is possible?

4
What do we want to measure ?
  • Brainstorm ..
  • Temperature - neutrons
  • Density - helium
  • Impurities - pressure
  • Current - electric field
  • Magnetic field - Rotation
  • Radiation - Plasma position
  • ..and many more things..
  • and its profiles
  • and its time evolution ..

5
What can we measure ?
  • Fields
  • Radiation
  • Particles

6
What can we measure ?
  • Passive Methods
  • Magnetic coils
  • Spectroscopy
  • Mm wave emission
  • Neutral Particle analysis
  • Thermography
  • Active Methods
  • Interferometry
  • Polarimetry
  • Reflectometry
  • Thomson Scattering
  • Charge Exchange Spectroscopy
  • Laser induced fluoresence
  • Heavy ion beam probe
  • Pellet injection
  • ..many more..

7
Why do we want to measure this ?
  • Machine control
  • Plasma position
  • Bt, Ip, ne
  • ? feedback control
  • Physics understanding
  • profiles, time evolution, fluctuations

8
Examples
9
Interferometry
  • Refractive index of plasma
  • Nkc/w (1- wp2/ w2)1/2 ? 1- wp2/ 2w2
  • (for perp. propagation, O-mode)
  • IR wavelength O (100 mm)
  • Phase shift
  • Line integrated signal

10
Interferometry
  • Mach-Zehnder interferometer

Shortcomings - fringe jumps - amplitude
variations due to absorption/refraction
11
Geometry
  • Flux surfaces
  • 1D,2D,3D, ..

scattering
Local
Line-averaged
Multi-chord
tomography
12
Abel inversion
  • Theory abel-inversion
  • shortcoming
  • Hollow profiles

13
Density measurement
  • TEXTOR setup Typical Measurement

14
Polarimeter
  • Principle polarimeter
  • Linear polarized wave
  • Different refractive index of the two circular
    components
  • X en O-mode
  • ? Faraday rotation
  • For propagation
  • parallel to magnetic field

15
Polarimeter
ITER
  • Setup - polarimeter

16
Temperature Measurements
  • Thomson scattering Te (z)
  • high localization, high accuracy, no calibration
  • low (no) repetition rate
  • Electron Cyclotron Emission (ECE) ?Te (r)
  • high repetition rate, good localization and
    accuracy
  • difficult calibration, only optically thick
    plasmas
  • Charge Exchange Spectroscopy ? Ti

17
Thomson Scattering
  • Electrons scatter photons from laser puls
  • ? observed photons Doppler shifted
  • Spectrum represents
  • velocity distribution
  • ? width ?Te
  • number of scattered
  • photons ne

18
Thomson Scattering
  • Intensity of scattered light ne
  • For maxwellian EVDF, width of scattered spectrum
    Te
  • Relativistic effects are important for Te gt 0.5
    keV (mass / headlight)
  • Scattering yield is very lowPs/P0 2 ? 10-15
    for ne 5 ? 1019 m-3, DL 5 mm,W 5 ? 10-3 sr
    and 20 transmission of optical system
  • Excellent spatial resolution (mm range)
  • Bad time resolution

19
Thomson Scattering
  • Typical Setup
  • 25 J Ruby Laser
  • (694.3 nm)
  • Presently under
  • Development
  • Multi-burst system

20
Thomson Scattering
  • Typical Setup

21
Thomson Scattering
  • Example Textor

22
Thomson Scattering
Two Te profiles in a single shot, just before
and after a sawtooth crash
Te and ne profiles for a plasma with m2 islands
with peaked ne inside the island
23
Thomson Scattering
LIDAR
LIght Detection And Ranging features 180
scattering Time-of-flight information of
scattering from short pulse (300 ps ? 9 cm)
gives position information
LIDAR system at JET
24
Electron Cyclotron Emission
  • cyclotron motion
  • wce eB/gme ? emission in 100 GHz range
  • Radial resolved ? BB0R0/R
  • If density is sufficiently high large fraction
    of photons reabsorbed ? Equilibrium between
    radiation field and emitting/absorbing medium ?
    Blackbody Radiator
  • Planck
  • Raleigh-Jeans

25
Electron Cyclotron Emission
  • Optical depth
  • Resonances N1
  • Cutoffs N0
  • Use 2nd harmonic

26
Electron Cyclotron Emission
  • Localisation
  • harmonic overlap
  • relativistic effect wce1/g ? R, few cm r
  • Doppler broadening (antenna)
  • ECE-I
  • 2D array
  • Example TEXTOR

27
Electron Cyclotron Emission
28
Reflectometry
  • Inject mm waves into plasma
  • reflection at wpe
  • optical wavelength
  • determines position
  • of reflection
  • A) interferometry
  • B) Pulse radar
  • Also for fluctuation
  • studies!

29
Reflectometry
  • Fluctuations

30
Active Beam Spectroscopy
  • H0/D0 beam injected to heat plasma
  • Energy 50-100 keV/amu
  • Also Diagnostic capabilities
  • Charge Exchange Recombination Spectroscopy
  • Beam emission Spectroscopy
  • Motional Stark Effect Diagnostic

31
Charge Exchange Spectroscopy
  • resonant process
  • exchanged electron
  • in excited state
  • Maximum cross-section in
  • range 30-60 keV/amu

32
Charge Exchange Spectroscopy

33
Charge Exchange Spectroscopy

34
Charge Exchange Spectroscopy
  • High intensity
  • Local Measurement
  • Ti(r)
  • V(r)
  • nz(r) ? also He!

35
Charge Exchange Spectroscopy
  • But also complications
  • passive line
  • other spectral lines
  • spectral deformation
  • - due to scx f (Erel)
  • - due to radial averaging
  • contribution from excited beam neutrals
  • beam attenuation
  • Zeeman/Paschen Back splitting

36
Charge Exchange Spectroscopy

37
Beam emission Motional Stark effect
Balmer a emission (n3?n2, 6562 A)

38
Motional Stark Effect

39
The magnetic field structure
40
The magnetic field structure
  • The magnetic field helicity is described by the
    safety factor q
  • The magnetic field structure is determined by the
    current density profile
  • Low rational q-values like 1, 4/3, 3/2, 2, 5/2,
    3, 7/2 are related to - MHD instabilities -
    the transport properties - barriers

41
Balmer-? line
  • Hydrogen or deuterium
  • Transition n3 ? n2
  • Balmer-? line

42
Motional Stark Effect (MSE)
  • ADVANTAGES
  • - local emission
  • - full profile

43
Motional Stark Effect (MSE)
  • ADVANTAGES
  • - local emission
  • - full profile

44
Motional Stark Effect (MSE)
  • ADVANTAGES
  • - local emission
  • - full profile

45
Motional Stark Effect (MSE)
  • ADVANTAGES
  • - local emission
  • - full profile

46
Different methods
  • polarisation of one line TFTR,
    DIII-D,JET,ASDEX
  • Stark splitting not sensitive to Bp

47
Different methods
  • polarisation of one line TFTR,
    DIII-D,JET,ASDEX
  • Stark splitting not sensitive to Bp
  • Intensity ratio I?/I? TEXTOR (ITER??)

48
Diagnostic information
  • The location of the observation volume
  • The absolute value of the magnetic field

49
Diagnostic information
  • The location of the observation volume
  • The absolute value of the magnetic field

50
Diagnostic information
  • The location of the observation volume
  • The absolute value of the magnetic field
  • The direction of the electric field

51
Diagnostic information
  • The location of the observation volume
  • The absolute value of the magnetic field
  • The direction of the electric field
  • The beam density

52
Diagnostic information
  • The location of the observation volume
  • The absolute value of the magnetic field
  • The direction of the electric field
  • The beam density
  • The composition of the injected beam

53
Diagnostic information
  • The location of the observation volume
  • The absolute value of the magnetic field
  • The direction of the electric field
  • The beam density
  • The composition of the injected beam
  • The radial electric field

54
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