XTOD Mirrors: Physics-based specifications, fabrication approach and expected performance

1. XTOD Mirrors: Physics-based specifications, fabrication approach and expected performance Lehman Review 11 July 2007 Michael Pivovaroff Contributors: R Soufli, P Stefan, J Krzywinski This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

2. Outline • Overview of mirror system layout • Mirror fabrication • Two-step approach • Physics drivers for specifications: • Substrate quality (figure and finish) and size • Reflective coatings • Performance modeling

3. Layout of mirror systems SOMS: 0.8 < E < 2 keV • Total of four mirrors (3 reflections) • Choose between 3rd and 4th mirrors HOMS: 2 < E < 24.8 keV • Two mirrors/two reflections • Withdraw 1st SOMS mirror to access beamline

4. SOMS-1 HOMS: Hard X-ray offset mirror system • Periscope design, 30 mm horizontal offset • Withdraw first SOMS mirror to send hard beam to Fall Experimental Hall (FEH) HOMS-2 1.324 mrad incident angle 30 mm HOMS-1 11.333 m

5. SOMS: Soft X-ray offset mirror system • Three reflection design to maximize horizontal deflections • Creates two lines in Near Experimental Hall (NEH) • Translate last pair of mirrors to select line SOMS-3/4 13.9 mrad incident angle 570 mm SOMS-2 SOMS-1 11.5660 m

6. Overview of mirror fabrication • Must use FEL-proof materials (e.g., Be, B4C or SiC) for reflective surface • Impossible or infeasible to procure as monolithic mirrors • Instead, deposit thin films on Si substrates using LLNL expertise and facilities

7. LLNL magnetron sputtering • Developed for EUVL program; most recently, delivered optics for NASA solar observatory • System can fit multiple large-area substrates in a single deposition Underneath view of LLNL chamber lid with 5 sputtering targets

8. Risk mitigation for coatings • SOMS will use B4C; HOMS will likely use SiC • No way to tests coatings under exact X-ray FEL conditions; • Test thin films at FLASH • Damage occurs well-above LCLS operational conditions; • Agrees well with theoretical expectations (Hau-Riege et al., Ap Phys L, 90, 173128, 2007) • Lifetime testing of ~1 year shows no changes in B4C film properties • Identified deposition parameters to minimize film stress

9. Specifications: underlying philosophy • Captured in Physics Requirement Document (SOMS complete; HOMS will be signed this week) • Principal is to minimize impact of mirrors • Maximize throughput (high reflectivity, sufficiently long mirrors) • Limit increase in beam size • Minimize wave-front distortions • Balance against state of the art vendor capabilities • Start with metrology data from recent mirrors delivered to SSRL

10. Specifications: detailed • Details presented at October 2006 Lehman review • Power spectral density well-described by power law • Use formalism developed by Church & Takacs (and others) • Look at errors in three spatial frequency regimes; same for both SOMS and HOMS • High-spatial (finish): 0.5 μm-1 – 50 μm-1 σ 4Å rms • Mid-spatial: 10-3μm-1– 0.5 μm-1 σ 2.5Å rms • Low-spatial (figure): [clear aperture]-1– 10-3μm-1 0.25 μrad rms (slope errors)*  20 Å rms (height errors)* * vendor limited

11. Optical profilometry (Zygo) AFM Full-aperture interferometry Validation of approach (1) • Request coupons from potential vendors • Four vendors provided samples • Perform metrology at LLNL

12. Validation of approach (2) • Vendor 1 slightly better in mid- and high- spatial frequency ranges • Two vendors can meet our specs

13. SOMS details • SOMS mirrors ordered from InSync at the end of June • SOMS characteristics: • 250 mm long; 175 mm long clear aperture • Ensures at least 95% of beam captured (increases with energy) • Operates at 13.9 mrad incidence angle • 500 Å thick B4C coating • Good 3rd order harmonic rejection

14. SOMS reflectivity Primary pass-band 3rd harmonic pass-band

15. HOMS details • HOMS system concept review (SCR) scheduled for late July • HOMS characteristics: • 450 mm long—limited by coating facility • 50% of beam captured at 2 keV; 100% of beam captured at 8.3 keV • Operates at 1.324 mrad incidence angle • 500 Å thick SiC coating [candidate: TBR] • >94% throughput at all energies • Other options can increase throughput to 98%

16. HOMS reflectivity

17. Modeling update • Combination of ray-tracing, analytic codes and first-principle calculations used to assemble performance • Will integrate all components into comprehensive end-to-end simulation • Options: (1) insert relevant physics into existing LCLS Monte Carlo package developed by XTOD or (2) fold in models of spontaneous + FEL emission into ray-tracing codes

18. Six-month outlook • SOMS substrates at LLNL; coating possibly underway • HOMS substrates ordered; SiC deposition process and parameters optimized • Progress on an end-to-end performance model