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NICADD/NIU Accelerator R&D Proposal*

This proposal aims to benchmark flat-beam simulation codes against FNPL experiments to optimize beam quality. Challenges include space charge and RF focusing, which introduce nonlinear forces. Studies of bunch compression and coherent synchrotron radiation will also be conducted. The proposal includes procuring a new interferometer and developing a low-wakefield chamber for electro-optic diagnostics.

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NICADD/NIU Accelerator R&D Proposal*

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  1. NICADD/NIU Accelerator R&D Proposal* • Two Component Program : • Benchmark flat-beam simulation codes vs. FNPL experiments. • Only facility presently configured for flat-beam generation • Develop electron-beam diagnostics: • Single-shot interferometer w/ 3.3mm to 20 mm range. • Electro-optic crystal with low-wakefield vacuum chamber. *For Court Bohn

  2. Flat Beam Goal: Eliminate e- damping ring : εy/εx~ 100 with εgeom~ 1 μm/nC. Achieved to date: εy/εx ~ 50 with εgeom ~ 6 μm/nC. Key Question: How to optimize beam quality with flat-beam transformation?Simulations are needed to guide improvements!

  3. Challenges for Simulations • Complication: Space charge, rf focusing “ruin” the linear round-to-flat transformation by introducing nonlinear forces. • Codes that include these nonlinear forces are, e.g.,: PARMELA, ASTRA, HOMDYN. • Canonical simplification: cylindrical symmetry ⇒ codes must be generalized. Authors of ASTRA, HOMDYN are working on generalizations. • NIU proposes to benchmark generalized codes against FNPL experiments.

  4. Studies of Bunch Compression • Coherent synchrotron radiation and other wakefields complicate • bunch compression, e.g., microbunching can arise: Energy fragmentation of compressed bunch as seen in FNPL: Beam Energy ~ 15 MeV Bunch Charge ~1 nC E • Dynamics are sensitive to phase space input to the bunch compressor • Careful measurement of input & output longitudinal phase space needed • One viable option: far-infrared interferometer to measure coherent • synchrotron from thin film transition radiation

  5. NICADD/NIU/Georgia* Procuring New Interferometer Woltersdorff beamsplitter, purged, reference detector Optics diameter: 75 mm Dimensions: 30cm x 15 cm x 15 cm Frequency range: 3 cm-1 to 500 cm-1 (3.3 mm to 20 mm). Translation stage: 20 mm travel, 2 mm accuracy. CTR: Coherent Transition Radiation S: Beamsplitter M1: Mirror on Translation Stage M2: Fixed Mirror, Semi-Transparent PM: Off-Axis Parabolic Mirror DET: Detector Module *Uwe Happek

  6. Interferogram Autocorrelation Energy spectrum Bunch Density (Hilbert transform of energy spectrum) (Fourier transform) What Does an Interferometer Provide? [P. Piot, et al., Proc. PAC’99, 2229 (1999)] • Resolution of fine structure requires access to short wavelengths, • Existing interferometers average over many bunches, not single shots.

  7. Proposal for Future Interferometry • Develop single-shot capability with U. Georgia: • - multichannel detector based on mirage effect • (heated air above detector is probed by laser beam); • - preserve compact size (existing FIR multichannel • detectors are large). • Possibly procure second Michelson interferometer for • simultaneous input/output phase-space measurements.

  8. A SECOND ALTERNATIVE: ELECTRO-OPTIC DIAGNOSTIC [M.J. Fitch, et al., Phys. Rev. Lett.87, 034801 (2001)] • Major Advantage: Noninvasive • (Does not intersect beam.) • Works via Pockels effect: • Electric field modifies • dielectric tensor; • Laser beam monitors • the modifications. • Potential: Direct time-domain • observation of beam field, • Butchamber wakefield must be • small! NIU proposes to build and implement a low-wakefield chamber.

  9. Personnel: • Court Bohn, Nick Barov • Daniel Mihalcea, Yang Xi, Simulations Post-doc TBD • Two Graduate students • Facilities & Computing Resources: • FNPL: Photoinjector, new interferometer • NIU: System Operator, 16 Node 1.4 GHz Farm • Budget: • Grad student, simulations, 9 mo. $18,000 • Grad student, optics, 9 mo. $18,000 • Hardware $15,000 • Total $51,000

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