Non-intercepting Beam Size Monitor using Optical Diffraction Radiation

1. Non-intercepting Beam Size Monitor using Optical Diffraction Radiation Tanaji Sen FNAL for A. Lumpkin, R. Moore, V. Scarpine, T. Sen, R. Thurman-Keup, M. Wendt US LARP Collaboration Meeting, April 24, 2008

2. Outline • Background on ODR • Critical parameters • Far-field spectrum • Near-field spectrum • ODR Monitor in the Tevatron • ODR in the LHC • Proposal ODR Monitor

3. Progress since October 2007 • Detailed report on far-field ODR (LARP doc 711) • Near field spatial distribution (A. Lumpkin) • Synchrotron radiation background (R.Thurman-Keup) • Collaboration on ongoing experiments at JLAB, DESY (A. Lumpkin) • Mechanical design started • Space allocated in Tevatron • Decision on installation schedule (Spring 2009) ODR Monitor

4. What is ODR? • Generated when a charged particle passes near a conducting surface. • Non-invasive technique to measure beam properties. • Can be generated in a straight section unlike synchrotron radiation. • Backward ODR is imaged at the same longitudinal location as the target • Can be observed in the far-field (Fraunhofer zone) • Can be observed in the near-field (Fresnel zone) • Potential applications to Leptons: ILC, XFEL, ERLs, Muon collider Protons: Tevatron, LHC ODR Monitor

5. Brief History of ODR • Early theory developed in the late 1950s • Observation of coherent DR from electron bunch in 1995 • Observation of incoherent DR in the far-field from electron bunches in 2003 (KEK) • Beam size and position measurement in 2004 (KEK) • Interference between transition and diffraction radiation in 2005 (BNL) • Beam size and position measurement with the near field from electron bunches in 2007 (APS: Lumpkin) • Measurements at KEK, APS, BNL, DESY, CEBAF, … • 14 papers in Phys. Rev. Lett and PRSTAB since 1995, 6 in 2007-2008 ODR Monitor

6. Diffraction Radiation - Layout Camera 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 Target Proton beam Beam Effective source size at target = (γλ)/2π b Impact parameter Φ Target ODR Monitor

7. ODR critical parameters • Impact parameter b • Wavelength λ • Energy γ • ODR intensity is significant when b ~ γ λ/(2π) • Intensity falls when b >> γ λ/(2π) • Beam divergence << 1/ γ in hadron beams Transverse fields from a particle Ex ~ (x / r┴) K1(2πr┴/γλ) -> (x/ r┴(3/2))exp[-2 π r┴/(γλ)] ODR Monitor

8. Round hole: Far-field angular spectrum LARP doc 711 σ2 > σ1 • The angular spectrum peaks at ω= ωc • At fixed frequency, the ODR spectrum has peaks at θ ~1.6/γ • The minimum and maximum values and the locations of the extrema are sensitive to the beam size and beam position. • Ratio of minima to maxima can be used to determine beam size. σ1 Angle Angle Relative frequency ODR Monitor

9. Round hole: far-field spectrum • Angular spectra (log scale) at 1 and 3 microns for Tevatron and LHC • At 3 microns, LHC spectrum is 4 orders of magnitude larger than in the Tevatron • The relative difference grows larger as the wavelength is decreased. ODR Monitor

10. Rectangular slit: far-field spectrum • Angular spectra at 1 and 3 microns for Tevatron and LHC from a rectangular slit. • Similar features as with the round hole ODR Monitor

11. Sensitivity to beam size LARP doc 711 P. Karataev et al PRL (2004) • Ratio of minimum to maximum increases quadratically with beam size • Sensitivity increases with frequency • Intensity changes at the few% level will detect beam size changes of fractions of σ Smaller relative beam size or larger separation b=8σ Measurement at KEK ODR Monitor

12. Round hole: Photon yields LARP doc 711 • Tevatron: σ=0.4mm at C0 • 6σ clearance =>λc=14μm (u=1) • => λ = 2.8 μm (u=5) ------------------------------- • LHC: 18m from IP with β*=0.25m (after IR upgrade), σ=0.8mm • 7σ clearance =>λc=4.7μm (u=1) • => λ = 0.94μm (u=5) Nph ~ exp[-1.8ω/ωc] for ω > ωc Photon yield/bunch/turn in a 10% bandwidth Tevatron: Integrating over 36bunches and 1 second amplifies this by 1.7x106 ODR Monitor

13. Tevatron: Beam size from near field Tevatron examples (γ=1044, λ=1.6 µm) for beam-size monitor Left: σx=400 µm and varyingd from 2-8 mm, Right: σx=400 µm ± 20%, σy=400 µm, d = 6 σy. Courtesy of C.-Y. Yao, ANL Perpendicular polarization ODR Monitor

14. LHC: Beam size from near field LHC examples for beam-size monitor for σx=800 µm and varying d from 4.8-8 mm (L), and with σx=800 µm ± 20%, σy=800 µm, d = 6 σy, λ=1.0 µm, and γ=7500 (R). Perpendicular polarization Courtesy of C.-Y. Yao, ANL ODR Monitor

15. Beam position from near-field OTR and ODR image centroid track BPM – see A. Lumpkin’s talk (CM10) ODR Monitor

16. Place for ODR in the Tevatron Proposed C0 Section for Installation Courtesy: K. Duel • Space exists at C0 within a drift space for an ODR monitor • For protons, the nearest upstream dipoles are 11m away and they are weak • The synchrotron light monitor is close by and can be used for cross-calibration. ODR Monitor

17. 3 600x10 24 3000 nm 3000 nm 24 3 400x10 22 500 20 20 300 400 18 Photons / s / 0.1%bw / mm 16 Photons / s / 0.1%bw / mm 300 16 200 14 200 mm 12 mm 100 2 12 2 100 10 0 8 0 8 6 4 4 2 0 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 0 mm -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 mm Synchrotron radiation background Vertical polarization with mask Vertical polarization (3 microns) Courtesy: R. Thurman-Keup ODR Monitor

18. 24 1000 nm 1000 nm 24 3 22 40x10 3 40x10 20 20 30 18 30 16 Photons / s / 0.1%bw / mm Photons / s / 0.1%bw / mm 16 20 20 14 mm 12 mm 12 10 2 2 10 10 8 0 8 0 6 4 4 2 0 0 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 mm mm SR background at 1 micron Vertical polarization with mask Vertical polarization (1 micron) Courtesy: R. Thurman-Keup ODR Monitor

19. ODR Schematic/ OTR monitor OTR monitor in the Tevatron at E0 ODR Monitor Courtesy: V. Scarpine

20. Mechanical drawing of 10 way cross Courtesy: K. Duel ODR Monitor

21. ODR Monitor in the LHC • ODR monitor would be stationed between the detector and 1st quadrupole – left and right side of IR • From β(-L), β(L) we can measure β*,α* • Not affected by errors elsewhere in the machine. • Non-invasive measurement of beam size and relative beam position during a store. • Regular arc dipoles are ~260m from IP ODR monitor ODR Monitor

22. Pros/Cons of ODR in the LHC Pros. • Non-invasive measurement of the beam size at the IP • Measurement itself will not be influenced by optics errors • This can be used to diagnose gradient errors in the IR. • Relative beam position measurements can be compared against BPM measurements in the IR. • Bunch by bunch measurement may be possible Cons • Slower than synchrotron light monitor. Signal will have to be integrated over several turns. • Errors associated with the measurement are not well known. Measurements in the Tevatron will determine the limits of resolution. • The ODR monitor would be installed between the TAS and the 1st quad. Impact on the machine-detector interface needs to be better understood. ODR Monitor

23. ODR Monitor proposal • Goal: To demonstrate the feasibility of ODR to measure beam size and position in a collider. • Steps (1) Design the ODR monitor for the Tevatron (2) Install monitor at C0 in Spring 2009 (next shutdown) (3) Set up monitor for proton beam measurements during shot set-up and beam studies (4) Proceed to use the monitor during luminosity stores (5) Design an ODR monitor for LHC parameters ODR Monitor

24. Features of ODR Proposal • First test of ODR in a collider. The Tevatron offers a unique opportunity to further develop ODR – but the window is short. • Well defined start and end of task - Design and build now, install in Spring ‘09 - Ends with the Tevatron run in ‘10 • ODR/OTR experts involved Budget request • FY09: Labor: 1 FTE (to support 4-5 people), M&S: $50K • FY10: Request will depend on progress in FY09, will be mostly for labor. ODR Monitor

25. People • A. Lumpkin, V. Scarpine, T. Sen, G. Tassotto, R. Thurman-Keup, M. Wendt • Tevatron dept. • Mechanical Engineering dept • Look forward to a collaboration with CERN • Experts from other US labs welcome ODR Monitor

26. Summary • ODR has the potential to become a standard diagnostic tool • Proposed ODR monitor in the Tevatron will be the first test with a circulating beam. • LARP support is essential for test to proceed. • Success in the Tevatron will advance the state of the art. • ODR signals in the LHC will be orders of magnitude stronger than in the Tevatron at the same wavelength, or use lower wavelengths (~1/3rd) in the LHC • Imaging near the IP will provide an independent way to optimize luminosity ODR Monitor

27. Backups ODR Monitor

28. Measuring β*, α* • Beam size, hence β, is measured at +L, -L • α* = [β(-L) – β(+L)]/4L • β* = ( [< β>2 + 4(1+ α*2)L2]1/2 - < β>)/2) • < β> = [β(-L) + β(+L)]/2 • This measurement of β*, α* is independent of optics errors ODR Monitor

29. Signal Intensity Levels Estimated Estimated signal has strong dependence on αb=2πb/γλ. FLASH, 0.8 µm LHC1, 1.6 µm LHC-2, 1.0 µm Log10α2K12 b values Tev-2,1.6 µm Tev-1,1.0 µm Units of 2πb/γλ Courtesy of Yao, Lumpkin ODR Monitor

30. 25 6 12x10 3000 nm 20 10 15 8 25 3 500x10 10 3000 nm 6 20 5 400 4 15 Photons / s / 0.1%bw / mm mm 0 2 300 10 2 -5 -10 5 0 200 Photons / s / 0.1%bw / mm -15 mm 0 100 2 -20 -5 -25 0 -10 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 mm -15 -20 -25 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 mm SR background- wide views 3 microns Total Intensity Vertical polarization ODR Monitor