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Accelerator Research Department B

Accelerator Research Department B. E-163 Micro-buncher. C. Sears, E. Colby, C. Barnes SLAC / ARDB Feb 18, 2003. Accelerator Research Department B. Motivation. Injector system produces bunches of length 5 ps or 1.5 mm

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Accelerator Research Department B

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  1. Accelerator Research Department B E-163 Micro-buncher C. Sears, E. Colby, C. Barnes SLAC / ARDB Feb 18, 2003

  2. Accelerator Research Department B Motivation • Injector system produces bunches of length 5 ps or 1.5 mm • Optical wavelength = 800 nm, or ~2000 wavelengths over length of initial bunch • To optimize acceleration in accelerating structures, introduce electrons as micro-bunches, with separation = accelerating field frequency

  3. Accelerator Research Department B Schematic for Optical Bunching Technique 8 cm ~12 cm Compressor Chicane IFEL Christopher Barnes 8 February 2002

  4. Accelerator Research Department B Micro-bunching in phase space ~1 psec ~3 fsec ~7 fsec 8 cm ~12 cm Compressor Chicane IFEL Christopher Barnes 8 February 2002

  5. Inverse FEL Parameters Magnet: - 1.8 cm period - 3 periods - 0.5 T on-axis peak field (aw = 0.45) ***This gives overall small energy modulation. Necessary since signature from acceleration also small. We use chicane to transfer small energy modulation into position distribution (i.e. micro-bunches)

  6. IFEL Magnet IFEL Magnet Dimensions • Totals: 52mm x 40 mm x 860 mm • Gap: 8 mm • Iron width: 3 mm • Main magnet width: 6 mm Tapered end magnets • Magnet 1: 4.7 mm • Magnet 2: 1.5 mm Mirror plates for clean truncation of fields. -light blue: steel -dark blue/red: magnets (±polarity)

  7. Magnet Field Simulations Tapering of end magnets gives ½ area peaks to keep bunch on-axis as it traverses magnet. - Fields were produced using Mafia - FEL performance analyzed in Genesis Negligible Bx fields (<10 gauss for |x| < 1 cm)

  8. Field Simulations 2: Focusing Effects • Vertical focusing. f  6.5 m (negligible compared to upstream quads) -no horizontal defocusing seen above numerical noise of simulation

  9. Tolerance Issues 1) Magnetization vector mis- alignment: studied fields produced when magnetization vectors are 5° off of beam axis. Fields were unchanged in gap ( iron dominant). 2) Magnetization strength errors: Gave individual magnets ±5% strength errors. While fields were noticeably changed in gap, emittances and FEL performance were unchanged. Electron energy modulation of optical cycle for ideal undulator and case of magnetization strength errors = 5%

  10. Saturation Relative permeability on the poles of undulator Some saturations problems near sides of undulator. Unimportant since far removed from beam-line. Btotal near edge of undulator

  11. Micro-bunching at ORION The requirements for micro-bunching are the same as those for E163 in large. Greatest concern is successful beam-bunch overlap. 1) laser jitter is comparable to bunch length. Diagnostics equipment such as the streak camera are necessary to confirm beam-bunch overlap within the undulator magnet. 2) Other alignment features necessary to obtain transverse overlap of the beam & bunch. This is more of concern within the undulator since beam & bunch must interact over a greater distance.

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