1. ASIPP HT-7 & EAST Research status of First Mirror and proposals for the HT-7 experiment J.L Chen ( 陈俊凌）， M.Q Tan ( 谭模强） Outline 1. Introduction 2. Sputtering by CXA (Mirror materials selection production, test) 3. Deposition of contaminants (In-vessel mirror tests) 4. Cleaning of mirrors Laser ablation and GD cleaning of deposits 5. What can we do? 6. Proposals for the HT-7 experiment

2. Introduction HT-7 & EAST Neutron Working Group Thomson scattering Working Group Spectroscopy Working Group Working Group on Beam-Aided Spectroscopy and NPA Reflectometry Working Group First Mirror Working Group Radiation Effects Working Group International Diagnostic Database Working Group Specialists Working Groups on Diagnostics First Mirrors (FM) also as five High Priority Topics in SWG

3. ASIPP HT-7 & EAST All diagnostics in ITER which uses radiation in the ultraviolet, visible and infrared wavelength range will have to view the plasma via a mirror. These first mirrors must survive in an extremely hostile environment and maintain an acceptable optical performance.

4. ASIPP HT-7 & EAST First mirror be exposed to neutron,  particle, CXA,  -ray,  - ray…. The wavelength range of interest is from 5 nm in vacuum UV region up to 100 mm in the far infrared range. The requirement is to maintain a mean surface roughness which does not exceed 0.1 of the operating wavelength. Mirrors used for diagnostics in present magnetic confinement experiments would not maintain the required performance for more than a few tens of seconds under these conditions. UV and X-ray radiation ~up to 500 kW/m 2, surface heating; Neutron flux up to 8 W/cm 3, mainly volumetric modifications of the material; Charge exchange atoms - up to 23*10 19 particles/(m 2 *s) with energies0.1-several keV; Deposition of material eroded from the divertor and first wall. Particle flux: Neutron and CXA is the most important Reflectivity Resistance to CXA Consideration

5. Sputtering by CXA HT-7 & EAST Neutron irradiation does not result in the direct degradation of reflectivity, but accelerate the CXA sputtering. Different sputtering yield in different orientation Appearance of Step structure (microrelief) Degradation of Reflectivity CXA Al mirror has the lowest resistance, lost a large portion of reflectivity ~0.2  m, fully degraded h>0.4  m. Cu lost 70%, ~0.8  m. The rate of R(h) dependence for W and Ta (after maximum) mirrors looks rather similar to R(h) dependence for the later stage of sputtering of a Cu mirror. Rh film on Cu substrare maintained its initial R after ~7  m sputtered. No any noticeable degradation of reflectance ~5(for mono W) and ~7(Mo)

6. ASIPP HT-7 & EASTAg,Au,Cu higher reflectivity but lower resistance to sputtering. W,Mo,SS lower reflectivity but higher resistance to sputtering. Mirrors must be fabricated either of monocrystalline metal (Mo or W), or as a metal film on metal substrate (Rh is probably the best candidate) with the film thickness depending on the mirror location relatively to the core plasma, i.e., depending on the degree of attenuation of the CXA flux to the mirror surface.

7. ASIPP HT-7 & EAST Materials selection of FM Development of the technology of mirror preparation (bulk mirrors and metal film on metal substrate mirrors) Simulation experiments the long-term sputtering tests are being conducted for mirrors of different metals with different structure: (i)Polycrystalline (Be, Al, SS, Cu, Mo, Ta, W); (ii)Monocrystalline (SS, Mo, W) ; (iii)Metal film on metal substrate (Be/Cu, Cu/Cu, Rh/Cu, Rh/SS, Mo/SS, Mo/Mo). The energy distribution of ions of deuterium plasma is wide (0.1-1.5 keV)

8. ASIPP HT-7 & EAST Reflectance of mirror samples before (dotted) and after (solid) exposure to one year of Tore Supra plasma (B. Schunke, V. Voitsenya)

9. ASIPP HT-7 & EAST SEM photo of polycrystalline Cu mirror after layer of  2.5  m was eroded by ions of deuterium plasma Scanning electron micrographs of the surfaces of W(a,b) and Ta(c,d) mirrors after sputtering layers with thickness: (a)870nm;(b)2710nm;(c)960nm;(d)297 0nm.

10. ASIPP HT-7 & EAST An extensive R&D program is on going in which candidate mirror materials are subject to energetic particle bombardment with ion sources and plasma simulators, and to environmental tests in tokamaks. The degradation of the performance of the mirrors is measured. Degradation of reflectivity of candidate first mirrors materials under energetic ion bombardment. After V Voitsenya, et al, RSI, 2001 Single crystal Polycrystal Molybdenum

11. Deposition of contaminants HT-7 & EAST The scheme of deposit appearing on the diagnostic window due to physical sputtering of the surface materials of the wall and the possible way to decrease the rate of deposit growing. 1 - periphery plasma, 2 - flux of CX atoms, 3 – diagnostic duct, 4 - sputtered atoms of a duct material, 5 – diagnostic window, 6 - deposit on the window surface, 7 – sputtered atoms of a deposit material, 8 - diaphragms made of material with low sputtering yield (e.g., Ta, W).

12. ASIPP HT-7 & EAST Mo mc 110 Acier 316L Cu OFHC Actual situation: Multiple effects occurring simultaneously

13. ASIPP HT-7 & EAST Results

14. ASIPP HT-7 & EAST

15. ASIPP HT-7 & EAST Direct comparative test of single crystal and polycrystalline mirrors under erosion conditions

16. ASIPP HT-7 & EAST Investigations of diagnostic mirrors in TEXTOR Outlook for 2005 ► Mirrors in the erosion conditions ● Direct comparative test of candidate mirrors. ● Impact of surface finishing on the optical performance of single crystal mirrors in the erosion conditions (collaboration with Kurchatov institute, Russia). ► Mirrors in the deposition conditions ● Modeling of plasma-gas interaction in the periscope mirror system with UEDGE code (collaboration with LLNL, USA). ● Modeling of impurity transport and deposition in the periscope mirror system with ERO code. ● Experiment on deposition mitigation in the Periscope-Upgrade mirror system.

17. ASIPP HT-7 & EAST Exposition of SS mirror samples in Large Helical Device (LHD) during 3rd experimental campaign (A.Sagara)

18. ASIPP HT-7 & EAST Retractable heatable mirror system Single crystal and polycrystalline molybdenum mirrors were exposed; Exposure in the Private Flux Region (PFR); Series of identical ELMy H-Mode discharges; Partially detached plasma in the divertor; 1st exposure: mirrors at room temperature; 2nd exposure: mirrors at 140 0 C→80 0 C.

19. ASIPP HT-7 & EAST Preparation of the First Mirror Test in JET: locations of cassettes with mirror samples.

20. ASIPP HT-7 & EAST Cleaning rate magnitudes around 1nm/min are relevant to what is known about chemical erosion in ECR plasmas. The rate of cleaning increases when the magnetic flux crosses the polluted area at the angle of incidence exceeding 30Deg. There is strong incentive to address the other types of discharge which show a promise as cleaning tool. Research on mirror Cleaning Sizable efforts were made to improve the cleaning ability of low temperature plasmas. Mirror in-situ cleaning shows a promise as a potential technique for ITER This could be laser cleaning (this possibility is under investigation in PPPL and in Kurchatov Institute). Flashlamp cleaning (Counsell UKAEA) - a Xe flashlamp close to the mirror but not blocking its view (the first pulse may be needed to clean the flashlamp itself!). Local discharge cleaning.

21. ASIPP HT-7 & EAST 2 Coated in magnetron plasma2 Coated in the T-10 discharges 1 original,3 after the removal of coating Deposition of contamination onto first mirror is another important degradation of reflectance. deposits not only decrease the reflectance of mirrors, but also distort the spectrum of reflected radiation because of interference. However the role of deposition of contaminants is still not clear for the FMs of the core plasma.

22. ASIPP HT-7 & EAST For the FMs of laser diagnostics, high repetition frequency of laser shots the thin surface layer of mirror is subjected to short-term thermal impacts with a resulting effect very much similar to a fatigue deformation. Laser tests were performed on first mirror prototypes to find the single shot damage threshold and multipulse laser damage threshold. Diffusion scattering coefficients via number of laser shots for sc Mo mirror under different laser fluence-0.78, 0.84, 1.25 J/cm 2

23. ASIPP HT-7 & EAST Scan-electron microscope photos of mirror surface, horizontal line gives a scale: (a)molybdenum single crystal, (b)molybdenum polycrystal. Electron microscope photo of single crystal Mo mirror surface after influence of multiple laser irradiation. Magnification: (a)100,(b)1000 times

24. ASIPP HT-7 & EAST First Mirror Programme Selection and use of materials that are resistant to erosion due to sputtering. Measurement on existing tokamaks under ITER like edge conditions. Development of models of the process. Development of mitigating methods (baffles, shutters etc) Development of cleaning techniques All are being pursued but not aggressively enough. Only the selection and use of resistant materials has really been covered adequately so far. The development of models is especially weak.

25. ASIPP HT-7 & EAST Actual situation: Multiple effects occurring simultaneously Time averaged measurements Poorly known edge plasma conditions Models at a very early stage of development Many experiments are ‘interpreted’ without the use of models.

26. HT-7 & EAST Research proposals in HT-7 experiment The fabrication of high quality mirrors: Material selection and the fabrication process.(polishing and cleaning) Thick films on metallic substrate. (Rh films or) Pre-characterization of mirrors should be made: Optical properties; Elemental composition of the mirror surface; Surface topography; Surface roughness curvature were investigated. What can we do?

27. ASIPP HT-7 & EAST Experiment: Erosion-deposition rate depend on position and material of mirrors, plasma parameters, VV conditioning modes and using mitigation measures. So the “history” of reflectivity deterioration of each mirror will be unique. 1. Mirrors were exposed for series of identical shots at the same plasma conditions in the SOL of HT-7. 2. Mirrors on sample rack of the removable midplane manipulator. Key: position and orientation. The position erosion equal to deposition. Study of composition and morphology of the deposits. Estimation of deposition rates on the mirrors. Investigation of mirror reflectivity degradation

28. ASIPP HT-7 & EAST Exposure on test limiter inclined at 20 0 with respect to totoidal direction. Averaged density; The number of shots, duration of exposure; average temperature of the leading edge. The temperature excursions up to. Numerical modeling.(ERO code, uedge code, EIRENE, BBQ ) Parameter

29. ASIPP HT-7 & EAST Polarimetry: characterization of retro-reflector exposed to plasma. Pre and post exposure mirror analyses Surface topography(roughness,flatness, profilometry-erosion) Surface analysis (EDS,XPS,SIMS,SEM), deposition measurements Deposition layer thickness measurements. Optical measurements( ellipsometry, reflectivity UV->FIR). Analysis methods Contaminants analysis:ERDA (Elactic Recoil Detection Analyses), RBS (Rutherford Back Scattering), SIMS, SEM, Profilometer, X-ray diffraction, film annealing. The relative reflectance was measured by means of a specular reflectance accessory of the Lambda 35 spectrophotometer.

30. ASIPP HT-7 & EAST Facility Experiment Aim of experiment DescriptionResults Wavelengt h range Implicatio ns for future studies HT-7 Planned Comparative test of PC molybdenum, PC Tungsten and fine grain Tungsten and stainless steel mirrors under erosion-dominated (r=28.5-30cm) conditions in the SOL of HT-7. Contact persons Junling Chen jlch@ipp.ac.cn To make the clear the correlation between environme nt conditions and behavior of optical properties of in- vessel mirrors of different materials. Mirror samples will be exposed on the midplane manipulator and exposed during the same discharges. SS Mirror installed at the inner wall, a little over the central plane of the device, ~5cm from the plasma and without any protection. Exposure time next whole experimental campaign. An extensive analysis of exposed mirrors and modeling of mirror exposures is foreseen. Detailed surface analyses by different techniques; 2-D profilometry ; reflectivity: 250-2500 nm, Polarization : 300- 20.000nm Competitiv e concept with Rh film mirrors should be addressed Presently under considerati on for next experiment al campaign

31. ASIPP HT-7 & EAST 谢谢大家！ Thanks for your attention!

32. ASIPP HT-7 & EAST