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Damage Considerations in FEL Source Propagation: Thermal Thresholds & Processes

This study examines damage processes in solids caused by FEL sources, considering thermal thresholds like pressure effects, spallation, and more. Results show that materials with high melting points and low atomic number are more resistant to damage, pointing to a thermal model that predicts safe material placement in the beam. Flash experiments confirm this model.

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Damage Considerations in FEL Source Propagation: Thermal Thresholds & Processes

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  1. Damage ConsiderationsDavid Fritz FEL Source Propagation Absorbed Energy Dose Damage Processes in Solids Damage Thresholds FLASH Results Summary

  2. Comparison to Synchrotron Sources Average heat load is not a concern but instantaneous energy deposition must be considered

  3. FEL Source Propagation A diffraction limited Gaussian source is assumed

  4. Peak Fluence

  5. Radiation Dose per Atom

  6. Solid State Damage Processes • Thermal melting • Presure effects • Spallation • Shear • Ablation • Non-thermal melting • Multi-pulse fatigue effects • Thermomechanical stress • Chemical • Phase transition

  7. Thermal Damage Thresholds Heat Capacity - Energy required to raise the temperature of one gram of a substance by 1° K. Enthalphy of Transformation (a.k.a. Latent Heat) – the amount of energy released or absorbed by a substance during a change of phase.

  8. Thermal Damage Thresholds (2) Beryllium Silicon

  9. Thermal Damage Thresholds (3) † Units of eV/atom * 8265 eV Photon Energy, 1.1 x 1012 ph/pulse

  10. FLASH Results • 32.5 nm wavelength • 25 fs pulse duration • 5.5 μJ pulse energy • B4C, C, Si, SiC were exposed to focused FLASH FEL • Up to 2.2 J/cm2 • Threshold for surface damage is on the order of the fluence required for themal melting S. Hau-Riege et al., Applied Physics Letters 90, 173128 (2007).

  11. Summary • Instantaneous energy deposition must be considered • High melting point, low-Z materials will be most resistent to damage • Thermal model predicts that some materials can be safely placed in the NEH and FEH beam at normal incidence • FLASH damage results are consistent with the thermal model

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