The ITER radiation environment for diagnostics

1. The ITER radiation environment for diagnostics G. Vayakis With apologies to A. Costley, E. Hodgson, C. Walker, K. Ebisawa R. Reichle, T. Nishitani and the many contributors to the ITER Nuclear Analysis Report N 55 RI 38 04-05-06 W 0.1

2. Outline • Introduction • Radiation environment • Radiation effects and affected components • Radiation R&D summary • Specific examples • Conclusions G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

3. Warning! • Radiation effects on diagnostics span a vast multidimensional space • My experience in this area has sampled small volumes of this space, both as a user and a generator of data • Your mileage will vary! G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

4. ITER parameters Radiation identified as a problem at global level: From NAR G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

5. Key environmental issues affecting diagnostic performance After a table by A. Costley G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

6. Radiation levels at ITER diagnostic locations • 40 + diagnostics addressing with 40 ++ measurements • 20 + ports of three different types • Large number of locations • Where • - First wall, in gaps, in divertor, behind blanket centre, behind blanket edge, in port, in port behind labyrinth… • What • Assembly level: coils, mirrors, shutters, windows, more complex units such as bolometers • Materials: metals, insulators, liquids,gases • How • - Physical properties: strength, brittleness, transport (electrical, thermal, Hall and cross terms), heating, optical transmission, parasitic current and light generation • When • During operation, over machine life, over maintenance period • DIFFICULT TO MAKE GENERAL STATEMENTS: G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

7. Flux gradients (1-D) From NAR G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

8. Variation of the source From NAR G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

9. Local variation behind blanket Depth into vacuum vessel Variation of nuclear heating near blanket gap along the toroidal direction (example). Peaking factor x 5 - 10 over 1-D calculation From NAR G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

10. Variation within ports (early MSE model) From NAR G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

11. Typical Numbers From A. Costley et al, ITER Diagnostics R&D, Fusion Engineering and Design (2001) G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

12. Lifetime examples • Life time of some key diagnostics components at neutron power density of 0.5 MW / m2 or neutron power of 450 MW • The fluence of 0.3 Mwa / m2 gives • 2 x107 s burn at 450 MW • The life time is mainly limited by radiation effects • except where shown with (). From A. K.Ebisawa et al, Plasma Diagnostics fro ITER-FEAT, HTPD 2000 G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

13. R&D approach for diagnostics • Use results of general ITER radiation R&D program • Suggest specific materials to be tested typical of present diagnostics • Look for specific effects mainly relevant to diagnostic (RIEMF, radioluminescence…) • Test prototype assemblies in a few cases • Testing has some limitations, so margins are needed… G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

14. 1st wall n, g spectra • Testing of materials and prototypes done using g sources, 14 MeV n irradiation facilities and fission reactors • Spectrum and fluence cannot be reproduced simultaneously • Residual uncertainty after R&D From NAR G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

15. Key radiation effect Summary Sheets (mainly R&D) • Ceramic insulators, and wires/cables • Mirrors and reflectors • Windows • Optical fibres • Complex assemblies • Example: Bolometers • Example: Magnetic coils G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

16. Ceramic insulators and wires • Several diagnostics will use ceramic insulators and wires; extensively investigated • Key effects: RIC, RIED, RIEMF, RITES • RIC can be rendered negligible by careful choice of materials • RIED is still not understood, but an extensive database has been established to guide design • RIEMF understood in general and can be modeled • Additional effects arise when wires are made into real circuits (RITES) G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

17. Mirrors and reflectors • Plasma facing optical element often a mirror. Lifetime a key parameter. • Extensive tests in which candidate mirror materials have been subject to different types and levels of radiation have been carried out • Nuclear heating can be a problem via distortion • Bulk metal mirrors: Neutron and g radiation not a threat • Dielectric coated mirrors + neutron irradiation can lead to flaking and blistering. Multi-layer mirrors ( X-ray ) can be affected by neutrons • careful choice of mirror material • guidelines have been developed. • Inorganic X-ray crystals (e.g. graphite) not affected. G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

18. Windows • Key effects: radiation induced absorption (instantaneous / permanent component), radioluminescence. • Optical properties tested in many materials • passive diagnostics by wavelength range: < 200 nm: absorption is very high without irradiation and direct coupling is necessary < 400 nm: both the absorption and luminescence are enhanced; further work required 400 nm to 5m: suitable materials found >5 m: ZnSe and diamond can work. mm-microwave diagnostics: no problems are anticipated. • Active diagnostics (high power): much lower tolerance to absorption < 5%. Further work is required to optimise the windows for such systems. • Thermal annealing can work for some materials G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

19. Example of annealing Absorbed dose is 0.3GGy(Si). The sample dimension is 16 mm in diameter and 8 mm in thickness. G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

20. Fibres • Used extensively for spectroscopy, Thomson scattering. Would like to use as far into the vessel as possible. • Optical path much longer than for windows: radiation induced absorption and radioluminescence more significant. Mechanical damage (embrittlement) possible. • Extensive R&D program, continuing • Substantial radiation induced absorption and luminescence occurs especially at short wavelengths (< 800 nm). Typical results are shown in figures 5.8-6 and 5.8-7. • In general, optical fibres cannot be used inside the vacuum vessel. • outside the bioshield may be able to use fibres at visible and longer wavelengths. • In the intermediate region may be possible at infrared wavelengths. More work is required to determine the optimum material and the precise magnitude of the optical properties. Should be application-specific. G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

21. Example of fibre luminescence G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

22. Assembly Example: Magnetic coils • RIC thought to be a problem • Measurements of insulators found Al2O3 good enough • RIED thought to be a problem • Measurements have tentatively identified safe design window (E, T, radiation level); design within it • RIEMF thought to be a problem • Measurements and calculations suggest RIEMF levels may be tolerable but RITES can be a problem. • More design and R&D needed From G. Vayakis et al, HTPD 2002 and this meeting G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

23. Assembly Example: Bolometers • JET-type bolometer design target • Mica initially thought to be a possible problem • Test on mica films in reactors suggest may be OK in ITER • Whole bolometer tested in reactor • Gold meander thought to have broken by a combination of embrittlement / transmutation and substrate swelling • More design and R&D planned: alternative meander (Pt) and substrates, alternative principle (Ferroelectric) G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

24. Lessons from personal radiation R&D involvement (user and generator) • Generic results only a rough guide to a very complex field • Can be difficult to find relevant results • Tracing references can also be difficult • Experts are heavily overloaded • Need for a radiation database just to document the ITER R&D and modeling results (underway within the ITPA framework) • Surprises await when whole assemblies are tested • Unless margins are very large, • Must make units maintainable or • test in reactors • But preferably both! • Radiation R&D takes a very long time • Planning must involve the key users • must not be left to the end G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1

25. And finally, some more thoughts (on a tangent) • ITER is test bed for a fusion reactor • These numbers still 0.5 -1 order of magnitude away from typical projected reactors • But diagnostics work at 1-2 orders of magnitude below 1st wall equivalent levels • IFMIF volume is limited and timing uncertain; materials testing a priority • Space at high flux available in ITER upper ports (even whole ports) • Much could be learned by using space to test key control diagnostic components (e.g. magnetic coils) near ITER 1st wall G. Vayakis, The ITER radiation environment for diagnostics, N 55 RI 38 04-05-06 W 0.1