1. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann1 Albrecht Herrmann EURATOM - IPP Association, Garching, Germany ITER Divertor Thermography Optical concepts

2. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann2 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

3. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann3 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

4. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann4 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, NAKA ITPA 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 grating

5. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann5 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. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann6 Selection criteria (without ordering and weighting) criteriaWLMFiberOptical ITER needsxx (?)x Radiation hardnessxx(-)x selection of detection wavelength -x(-)x Multi purpose use-x(-)x Optical performancex(-)xx Robustness against displacement ?xx? Reliabilityx?x Space savingxxxx

7. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann7 Need for flexibility in wavelength/bandwidth selection Temperature equivalent for bremsstrahlung. A constant pressure of n e T e = 1x10 22 eVm -3 is assumed. Adjust sensitivity and dynamic range Avoid parasitic radiation - bremsstrahlung Solid: BB radiator, F/# =2.8, Δt exp =1 μs, bandwidth=10% of wavelength Dashed: Factor 10 reduced performance ( τ*ε*Δt exp (μs) = 0.1) Preference for 5μm range

8. 6.-10. January 2008ITPA on Diagnostics, Philip Andrew, A. Herrmann8 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