6.-10. January 2008 ITPA on Diagnostics, Philip Andrew, A. Herrmann 1

Albrecht Herrmann

EURATOM - IPP Association, Garching, Germany

ITER Divertor Thermography

Optical concepts

6.-10. January 2008 ITPA on Diagnostics, Philip Andrew, A. Herrmann 2

3 concepts for ITER divertor thermography

• Wavelength multiplexing

– IPP Garching (H. Salzmann, A. Herrmann)

– ITER-NAKA (K. Itami et al.)

• Light transmission by optical fibres

– CEA-Caderache (R. Reichle et al.)

• 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 3

Tangential vs. radial (direct) view

• Clear defined geometry• Nearly perpendicular view• Short focal length and long optical

path • Large number of optical elements –

How to reduce?

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)

• 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 pro, con

JET AUG

6.-10. January 2008 ITPA on Diagnostics, Philip Andrew, A. Herrmann 4

Inverse spectrometer for beam collimation

Wavelength multiplexing system (DDD 5.5 - old ITER - H. Salzmann et al. )

Cons:•Mixing of wavelength

and spatial scale.•Spatial and spectral

resolution depends one

from the other.

Pros:•Collimated beam.•Less optical elements (compare to a conventional system)

Redesigned and improved for the new Divertor by K. Itami, NAKAITPA diagnostics Padua, EPS St Petersburg, Rev. Sci. Instr. 75(2004)4124

P1-P6 temperature measurement at different wavelength (3-5μm)

Entrance slit of the spectrometer grat

ing

6.-10. January 2008 ITPA on Diagnostics, Philip Andrew, A. Herrmann 5

Conventional optical approach

Light transmission by optical fibers

(CEA)• Cassegrain and aspherical

mirror as front-end• Followed by optical ir-fibres

Mirror based relays optics (IPP)• 3 stage relay optics, 12 elements,• Needs final optical design

Details: EFDA contract 02-1003 Details: EFDA contract 02-1004

6.-10. January 2008 ITPA on Diagnostics, Philip Andrew, A. Herrmann 6

Selection criteria (without ordering and weighting)

criteria WLM Fiber Optical

ITER needs x x (?) x

Radiation hardness x x(-) x

selection of detection wavelength

- x(-) x

Multi purpose use - x(-) x

Optical performance x(-) x x

Robustness against displacement

? xx ?

Reliability x ? x

Space saving x xx x

6.-10. January 2008 ITPA on Diagnostics, Philip Andrew, A. Herrmann 7

Need for flexibility in wavelength/bandwidth selection

Temperature equivalent for bremsstrahlung. A constant pressure of neTe = 1x1022 eVm-3 is assumed.

Adjust sensitivity and dynamic range Avoid parasitic radiation - bremsstrahlung

Solid: BB radiator, F/# =2.8, Δtexp=1 μs, bandwidth=10% of wavelengthDashed: Factor 10 reduced performance ( τ*ε*Δtexp(μs) = 0.1)

Preference for 5μm range

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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.

Comparison of 3 concepts