Transcript Concepts for ITER divertor thermography

ITER Divertor Thermography
Optical concepts
Albrecht Herrmann
EURATOM - IPP Association, Garching, Germany
6.-10. January 2008
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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3 concepts for ITER divertor thermography
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Wavelength multiplexing
– IPP Garching (H. Salzmann, A. Herrmann)
– ITER-NAKA (K. Itami et al.)
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Light transmission by optical fibres
– CEA-Caderache (R. Reichle et al.)
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Mirror based relays optics
– IPP Garching (A. Herrmann)
All concepts are using optical heads below ITER dome
6.-10. January 2008
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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Tangential vs. radial (direct) view
Tangential from the midplane (3D,
JET, ITER – midplane viewing
system, top view (US))
Optical front end in the divertor region
(2D, ASDEX Upgrade, ITER divertor
thermography)
AUG
JET
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Access easier (independent on div
modifications)
Long focal length for spatial res. (but part
of a wide angle viewing system)
3D geometry, tangential view
Mixing of toroidal and poloidal information
Changing spatial resolution
6.-10. January 2008
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Clear defined geometry
Nearly perpendicular view
Short focal length and long optical
path
Large number of optical elements –
How to reduce?
ITPA on Diagnostics, Philip Andrew, A. Herrmann
pro, con
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Inverse spectrometer for beam collimation
Wavelength multiplexing system (DDD 5.5 - old ITER - H. Salzmann et al. )
P1-P6 temperature measurement at
different wavelength (3-5μm)
Entrance slit of the spectrometer
Pros:
•Collimated beam.
•Less optical elements
(compare to a
conventional system)
Cons:
•Mixing of wavelength
and spatial scale.
•Spatial and spectral
resolution depends one
from the other.
Redesigned and improved for the new Divertor by K. Itami, NAKA
ITPA diagnostics Padua, EPS St Petersburg, Rev. Sci. Instr. 75(2004)4124
6.-10. January 2008
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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Conventional optical approach
Light transmission by optical fibers
(CEA)
• Cassegrain and aspherical
mirror as front-end
• Followed by optical ir-fibres
Details: EFDA contract 02-1003
6.-10. January 2008
Mirror based relays optics (IPP)
• 3 stage relay optics, 12 elements,
• Needs final optical design
Details: EFDA contract 02-1004
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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Selection criteria (without ordering and weighting)
criteria
WLM
Fiber
Optical
ITER needs
x
x (?)
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Radiation hardness
x
x(-)
x
selection of detection
wavelength
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x(-)
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Multi purpose use
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x(-)
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Optical performance
x(-)
x
x
Robustness against
displacement
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xx
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Reliability
x
?
x
Space saving
x
xx
x
6.-10. January 2008
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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Need for flexibility in wavelength/bandwidth
selection
Adjust sensitivity and dynamic range
Avoid parasitic radiation - bremsstrahlung
Solid: BB radiator, F/# =2.8, Δtexp=1 μs,
bandwidth=10% of wavelength
Dashed: Factor 10 reduced
performance ( τ*ε*Δtexp(μs) = 0.1)
Temperature equivalent for bremsstrahlung. A
constant pressure of neTe = 1x1022 eVm-3 is
assumed.
Preference for 5μm range
6.-10. January 2008
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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Comparison of 3 concepts
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The most flexible system with respect to wavelength and bandwidth selection is
the conventional mirror optics.
Discussed spectral measurements are applicable for the fiber optics solution as
well as for the conventional optics.
The advantage of the fibre optics solution is the mechanical flexibility and
tolerance against vibrations and displacements. A limiting factor for the usage of
fibers is the radiation induced degradation of the transmission.
Wavelength multiplexing links spatial and spectral resolution. The required
spatial resolution implies a bandwidth of a few tens of nanometers.
A mirror based optical transfer line did not suffer so much from radiation but it
has to be shown that there are simple methods for the alignment of the relay
stages to compete at this point with fiber optics systems.
6.-10. January 2008
ITPA on Diagnostics, Philip Andrew, A. Herrmann
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