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Proposal to Use Metallic Mirrors for MSE Continued

Proposal to Use Metallic Mirrors for MSE Continued. February 10, 2003 S. D. Scott PPPL. Optical Properties of Candidate Materials at 0.66 Microns. n (real) k (imaginary) Aluminum 1.55 7.9

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Proposal to Use Metallic Mirrors for MSE Continued

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  1. Proposal to Use Metallic Mirrors for MSEContinued February 10, 2003 S. D. Scott PPPL

  2. Optical Properties of Candidate Materials at 0.66 Microns n (real)k (imaginary) Aluminum 1.55 7.9 Silver 0.07 4.2 Gold 0.14 3.37 Iron 3.48 3.86 Moly 3.56 3.01 Austenitic 832 MV 2.6 4.5 MSE metal mirrors.ppt

  3. Silver has excellent reflectivity and superb S/P reflectivity Ratio Silver Reflectivity for s and p states Gold Aluminum SS832 M2, M3 angles (guess only) MSE metal mirrors.ppt

  4. Aluminum Provides Least Difference in Phase Aluminum Phase difference between Reflected s and p Gold M2, M3 angles (guess only) Silver SS832 MSE metal mirrors.ppt

  5. Phase of S and P states Aluminum SS832 Silver Gold M2, M3 angles (guess only) MSE metal mirrors.ppt

  6. Aluminum Perturbs Measured Angle the Least SS832 Aluminum Assume 5o input polarization angle Silver Gold M2, M3 angles (guess only) MSE metal mirrors.ppt

  7. n Serendipity: S and P Polarizations are Reversed at M2 and M3 Mirrors M2 emergent S P 45o P S 45o incident n incident … so to first order, the S/P reflectivity ratio and phase shift at a metal mirror don’t affect the relative amplitude or phase of the incident EM wave. There will be higher-order terms due to the variation of the S/P reflectivity ratio and phase shift with angle of incidence, since not all rays strike the mirrors at 45o. S P MSE metal mirrors.ppt

  8. Compute Distribution of Angles-of-Indcidence with Ray-Tracing Code (thanks to Bravenec) MSE metal mirrors.ppt

  9. There is Little Correlation Between AOI on M2 and M3 MSE metal mirrors.ppt

  10. Compute Net Reflectivity and Phase Shift for Each Ray Net result: fairly wide distribution of phase shifts among the various rays, but the average phase shift is reduced from a single mirror at 45o. MSE metal mirrors.ppt

  11. Compute Net Reflectivity and Phase Shift for Each Ray Net result: compared to aluminum, Silver has greater range of phase shifts and a larger average phase shift. MSE metal mirrors.ppt

  12. Comparison of Single Mirror to 2-Mirror Systems Phase Shift (degrees)S/P Reflectivity Ratio 1-mirror 2-mirrors 1-mirror 2-mirrors Aluminum 9.6 3.0-4.1 0.86 0.974-0.980 Silver 20.0 5.7-7.5 0.977 0.996 MSE metal mirrors.ppt

  13. Preliminary Conclusions • Metal mirrors would solve our mechanical problems, and their optical properties don’t necessarily preclude their use in MSE. • Aluminum (solid), or Aluminum, Silver, or Gold on Stainless look attractive: • All have high reflectivity • Aluminum perturbs apparent angle the least • Gold might not require a protective coating against oxidation. • We need to evaluate carefully: • Effect of change in polarization • Effect of two mirrors • Actual angles-of-incidence (ray tracing) • Requirements for alignment. • Compatibility of various substrate and coatings • Effect of unavoidable oxide coating and/or deliberate protective coating (e.g. SiO2). • Possible use of dielectric coating to reduce phase shift. MSE metal mirrors.ppt

  14. Motivation • Solid metallic mirrors (no glass component) would be immune from • the fracturing that has plagued us with the current glass components. • TFTR successfully used aluminum-coated (glass substrate) mirrors. • We have the option to lay down a film of silver, gold, aluminum etc • (or maybe dielectric coatings?) if the optical properties of the metallic • substrate are not ideal. • Have a list of vendors for metallic mirrors courtesy Dave Johnson. • Have software to compute the reflectivity and phase shift for s & p • courtesy of Fred Levinton. MSE metal mirrors.ppt

  15. Issues • Metallic surfaces have different reflectivities for s- and p- incident • polarizations  affects inferred pitch angle (effect can be “calibrated out”) • Note: we have two mirrors, whereas TFTR had only one. • Metallic surfaces introduce a phase shift  linearly polarized light • becomes partially circularly polarized. Loss of signal. • Reflectivity: silver and gold are excellent, aluminum is very good, • stainless steel is fair. • Oxide layers may form. Need to consider their optical properties • Must consider possible warping introduced by stresses induced • when solid mirror is bolted into place. • Calculate differences in reflectivity and phase shift as a function • of angle-of-incidence (about 45o for C-MOD MSE). MSE metal mirrors.ppt

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