Beam Imaging with Diffraction Radiation

1. Beam Imaging with Diffraction Radiation Tanaji Sen May 23, 2007

2. Diffraction Radiation Radiation emitted when a charged particle passes in the vicinity of a conducting target. Two cones (angle ~ 2/γ ) of radiation in the forward and backward direction Key parameters: the impact parameter, beam energy and wavelength of radiation Similar (and different) to transition radiation where a particle passes through the conducting target. Main advantage: Non-invasive (mostly!) Initial theory developed: ~ 1960s First measurements reported: ~1995 LARP Meeting - Diffraction Radiation

3. Possible Beam Diagnostics Diffraction Radiation Observables • Near field (at target) and far field intensity • Polarization • Frequency spectrum • Far field angular distribution These can be combined to measure • Beam size • Beam position • Beam divergence • Energy Easier with far-field (Fraunhofer diffraction) than with near-field (Fresnel diffraction) LARP Meeting - Diffraction Radiation

4. Diffraction Radiation - Layout CCD or PMT Filter Polarizer Far field imaging at KEK Phys. Rev Letters 90, 104801 (2003) 93, 244802 (2004) Near field image at APS PRSTAB:10,022802(2007) BDR 2Φ FDR Target Proton beam Beam b Impact parameter Φ LARP Meeting - Diffraction Radiation Target

5. KEK results Imax Imin LARP Meeting - Diffraction Radiation

6. Key parameters Choose: λ = 1000 nm (near IR); t = 2π b/γλ = 1; Intensity of DR ~ e-t = e-ω/ωc Impact parameter b = 15σ (LHC requirement) LARP Meeting - Diffraction Radiation

7. Required beam size • RHIC: At 4000nm, σ ~10 μm. Not feasible ? • Tevatron. At 4000nm, σ ~45 μm. Within ~0.5m from B0/D0 Min σ(arc) ~ 290 μm. Far infra-red? • LHC At 1000 nm, σ ~79. μm. Within 20m of IP LARP Meeting - Diffraction Radiation

8. IP5: Horizontal Crossing Angle Layout in the LHC IP1 : Vertical Crossing Angle BDR Cone Beam 2 b Target at 45 to beam direction b Beam 1 Location - Both beams should not arrive at the same time BDR Cone LARP Meeting - Diffraction Radiation

9. Further Developments Interference from multiple apertures Different Target Shapes to remove pre-wave zone effects Theory needs to be developed for - near field intensity with different aperture shapes - finite target size Beam Interference pattern is sensitive to beam divergence LARP Meeting - Diffraction Radiation

10. Criteria for ODR • What diagnostics does it realistically provide? • Precision and reliability of measurements (understand systematic and random errors) • Advantages/disadvantages of ODR • Impact on the machine and detector • Does it advance the start of the art? LARP Meeting - Diffraction Radiation

11. Next Steps • Explore the prospects of measuring ODR in a storage ring: Tevatron, APS, ALS, PEPII, …. • Develop an informal collaboration with US labs and CERN • Understand better the challenges of near field and far field imaging • Develop a proposal for experiments at an existing facility • Present proposal to the LARP collaboration for funding • Proceed with experiments • Develop ODR facility for the LHC LARP Meeting - Diffraction Radiation