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Short bunches in SPEAR

Short bunches in SPEAR. J. Safranek for the SPEAR3 accelerator group. Outline. Low alpha in SPEAR (X. Huang, J. Safranek) Lattice Bunch length measurements (J. Corbett et al.) Prospect of THz beamline (X. Huang) Edge radiation and synchrotron radiation Vacuum chamber shielding

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Short bunches in SPEAR

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  1. Short bunches in SPEAR J. Safranek for the SPEAR3 accelerator group J. Safranek CLS THz Workshop

  2. Outline • Low alpha in SPEAR (X. Huang, J. Safranek) • Lattice • Bunch length measurements (J. Corbett et al.) • Prospect of THz beamline (X. Huang) • Edge radiation and synchrotron radiation • Vacuum chamber shielding • Bunch profile, CSR enhancement J. Safranek CLS THz Workshop

  3. J. Safranek CLS THz Workshop

  4. Long lifetime • Good injection • Can run with alpha = 4e-6 or smaller J. Safranek CLS THz Workshop

  5. J. Safranek CLS THz Workshop

  6. a = 4e-6 J. Safranek CLS THz Workshop

  7. J. Safranek CLS THz Workshop

  8. Cross-correlation bunch length measurementCorbett et al. • Starved for photons • Average over many turns ~1 minute or longer • Would like to try with THz., single pass. J. Safranek CLS THz Workshop

  9. J. Safranek CLS THz Workshop

  10. SPEAR3 vacuum chamber J. Safranek CLS THz Workshop

  11. Dipole geometry Mirror center Source point Top of arc entrance lens The source point is at ¼ of the bending angle, or 0.38 m into the bend. The mirror center to trajectory exit is 78 mm. The full aperture at the mirror center is 58 mm. J. Safranek CLS THz Workshop

  12. Dipole entrance Dipole midpoint Dipole exit mirror Solid black is existing dipole chamber Dotted black is proposed chamber in THz dipole Red dot is beam position Dipole magnet pole face is red and blue. J. Safranek CLS THz Workshop

  13. Flux calculation,  = 1 mm Aperture 100 (H) x 46 (V) mrad2 Mirror is 0.5 meter from the dipole exit in SRW calculation.  = 1 mm Total flux on the mirror is 0.80E13 ph/s/0.1%bw Bend radiation Focused with a lens f=0.82 m, half of the distance to the source point (1:1 imaging) Total flux at the focused spot is 0.75E13 ph/s/0.1%bw Apparent SR source size J. Safranek CLS THz Workshop

  14. Flux calculation,  = 0.5 mm  = 0.5 mm Total flux on the mirror is 1.17E13 ph/s/0.1%bw Edge radiation Bend radiation  = 0.1 mm J. Safranek CLS THz Workshop

  15. Flux vs. wavelength H-polarized The flux is comparable to the chicane option. V-polarized J. Safranek CLS THz Workshop

  16. Shielding of ER and SR For near field ER For far field ER when • Wavelengths that are shielded by the far-field condition are shielded at the formation length, i.e., they won’t make out to the far-field zone at all! • Shielding occurs when the wall cut into the central cone of radiation. For SR, condition for shielding (far field) is h is full vacuum chamber height. ER SR Graph taken from R. A. Bosch, NIMA 482 (2002); reflection from two parallel plates was assumed. J. Safranek CLS THz Workshop

  17. Vacuum chamber shielding Edge radiation Assume full aperture Synchrotron radiation Most of ER with wavelength longer than 2 mm will be suppressed. Most of SR will pass through, up to wavelength of 4 mm. J. Safranek CLS THz Workshop

  18. Edge radiation from an enlarged ID port • Parameters • ER results =8.15 m, =5871, h=48 mm, d=10 cm (magnet edge length to bend angle of 1/ ), R0=1.5 m (aperture to edge), L=5.29 m (straight section length) The limiting aperture for ER is 48 mm (full) at 1.5 m downstream from the entrance edge of a SPEAR dipole. Edge radiation present for photon energy below it. In near-field regime for photon energy below it. Direct flux of ER through aperture for photon energy above it. No flux of ER through aperture for photon energy below it. J. Safranek CLS THz Workshop

  19. THz Power Integrated for wavelength 5 mm or shorter 1 ps rms, 5.0 A/bunch 1.7 ps rms, 17.3 A/bunch J. Safranek CLS THz Workshop

  20. THz power (<2mm wavelength) 1 ps rms, 5.0 A/bunch 1.7 ps rms, 17.3 A/bunch Wavelength>2 mm ignored in power calculation 372 bunches assumed J. Safranek CLS THz Workshop

  21. Conclusion, THz beamline • It is viable to extract dipole radiation for the THz beamline, with performance comparable to the chicane option. • Assuming 48 mm full aperture, SR of wavelength of 1 mm or shorter fully passes through; between 1 and 4 mm will partially passes through; longer than 5 mm will be suppressed by shielding. • ER of wavelength longer than 2 mm will be suppressed by shielding. • The port extracts mainly SR. • Integrated power is 120 mW for the 1 psrms bunch length mode, with 372 bunches, 5.0 A/bunch. J. Safranek CLS THz Workshop

  22. Reasons to build THz beamline • Characterize short X-Ray pulses (through spectroscopy of x-correlation/electro-optics) • AP CSR studies • THz for photon experiments Questions • How much stable CSR (mW) has been measured? How to calculate realistic performance? • Are linac-based sources better compared to bursting mode in storage rings? • How to optimize source? (Energy, dipole field & gap, chamber) J. Safranek CLS THz Workshop

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