ODR Diagnostics for Hadron Colliders

1. ODR Diagnostics for Hadron Colliders Tanaji Sen FNAL/APC Acknowledgements: A. Lumpkin, V. Scarpine, R. Thurman-Keup, M. Wendt

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 Initial theory developed: ~ 1960s First measurements reported: ~1995 ODR for Hadron colliders

3. Possible Beam Diagnostics Diffraction Radiation Observables • Near field (at or near target) intensity • Polarization • Frequency spectrum • Far field angular distribution • Interference between radiation from 2 sources These can be combined to potentially measure • Beam size • Beam position • Beam divergence • Energy Recent measurements at KEK, APS, FLASH Interest at other labs: CEBAF, BNL ODR for Hadron colliders

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 Target Proton beam Beam Effective source size at target = (γλ)/2π b Impact parameter Φ Target ODR for Hadron colliders

5. KEK results (slit target) ODR for Hadron colliders Imax

6. KEK Summary • Electron beam energy=1.28 GeV, γ=2505 • Bunch intensity = 1.2 x 1010 • Beam size = 10 μm, divergence= 3.8x10-3(1/γ) • Impact parameter ~ 5σy • Detected wavelengthλ = 0.56 μm • Synchrotron radiation background from dipole 8m upstream; used a mask • ODR intensity = 58% of OTR intensity • Measured sensitivity to beam size ~ 14 μm ODR for Hadron colliders

7. APS 10 σ 10 σ 10σ 16σ ODR for Hadron colliders

8. APS Summary • Electron beam energy = 7GeV, γ= 13,699 • Bunch intensity ~ 1.9x1010 (3 nC). Tevatron proton intensity ~ 43 nC • Beam sizes: σx = 1375 μm, σy = 200 μm • Typical impact parameter ~ 6 σy • Wavelength λ ~ 0.83 μm • ODR signals observed up to 16 σy • ODR signals (@ 6 σy) about 10% of OTR signal • Sensitive to horizontal offsets of 50-100 μm • Sensitive to beam size changes of 20-50 μm ODR for Hadron colliders

9. Hadron colliders: key parameters ODR for Hadron colliders

10. Different target shapes • Straight edge – APS (near-field), KEK (far-field) • Rectangular slit – KEK (far-field) • Round hole ODR for Hadron colliders

11. Round hole • Intensity distribution from a single particle (PSF) depends only on these parameters g, u, γθ • Otherwise it does not depend on the inner radius a< • Number of photons emitted (far-field) Inner radius a<. Outer radius a> Key parameters • Critical frequency ωc= γc/a< • Radii ratio g = a>/a< • Scaled frequency u = ω / ωc ΔNγ = (β/π)αf u2 F(g, u) Δω/ω ODR for Hadron colliders

12. Far-field spectral distributions (round hole) For g =1.1, Number of photons emitted /bunch/turn ΔNγ ~ 1.6 x 106 ODR for Hadron colliders

13. Rectangular Slit Angular spectral distribution from a bunch depends on • Slit width • RMS size • Bunch transverse offset • Observation angles θx, θy tx= γθx, ty = γθy ODR for Hadron colliders

14. Far-field spectral distributions (slit) TEV LHC Wavelength dependence Beam parameter dependence ODR for Hadron colliders

15. Far-field spectral distribution(straight edge) • Characteristic λc = 2πb/γ • At b = 4.8mm, λc = 28 μm (TEV) • Spectrum at ω > 0.2 ωc • Photon yield/bunch/turn • At ω = 2 ωc or λ=14 μm, ΔN = 4.4 x 106 photons/bunch/turn ODR for Hadron colliders

16. Interferometry • Forward DR from 1st target interferes with backward DR from 2nd target • Interference pattern is sensitive to beam divergence • Distance between targets should be comparable to far field distance. Rules this out for the LHC • May be difficult for very small beam divergences Interference from multiple apertures Beam FDR BDR ODR for Hadron colliders

17. ODR location in the Tevatron • Drift space around C0 is 11m • 4 dipoles upstream, 2 dipoles downstream in the proton direction • Beta functions are in the range 60-85m • Preferable to image pbars closer to the 4 dipoles ? 11 m protons Optics around C0 ODR for Hadron colliders

18. Empty space in C0 ODR for Hadron colliders

19. LHC Insertion • Regular arc dipoles are ~260m from IP • Weak separation dipoles (~1.5T) at 60m from IP • ODR monitor would be stationed between the detector and 1stquadrupole – left and right side of IR 260m 260m ODR for Hadron colliders

20. Measuring β*, α* -L L IP ODR for Hadron colliders 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

21. Layout in the LHC IP1 : Vertical Crossing Angle IP5: Horizontal Crossing Angle BDR Cone Beam 2 b Target at 45 to beam direction b Beam 1 BDR Cone ODR for Hadron colliders

22. Design decisions • Location of the target; both beams should not be present simultaneously, far enough from dipoles, … • Determine the synchrotron radiation background at the target • Determine the optimal shape and material of the target • Near-field/Far-field imaging or both • Determine the optimal wavelength range • If IR, deal with the challenges of IR detection (sensitivity, water vapor absorption, window material, …) ODR for Hadron colliders

23. Choice of window • Quartz has almost no transmission between 10 and 50 microns. Might work for RHIC (~140microns) • Diamond would be the material of choice for IR Courtesy: FLASH ODR for Hadron colliders

24. Goals for Tevatron measurements • Install ODR monitor in 2008 shutdown • Measure two beam parameters with good reproducibility for a single beam • Either beam size and beam position OR • Beam size and beam divergence • Measurements in both planes ? • Measure parameters for several bunches • Update measurements every N turns ODR for Hadron colliders

25. Pros and Cons of ODR in the LHC Pros. • Non-invasive • Beam size measurement near the IP on both sides, hence 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. • A tomographic reconstruction of transverse phase space may be possible from measurements over several turns. Cons • Slower than synchrotron light monitor. Signal will have to be integrated over several bunches. • Errors associated with the measurement are not well known at the moment. Installing a device in the Tevatron would determine the limits of resolution with this device. • 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 for Hadron colliders

26. Major LHC issues • What are the major benefits of imaging close to the IP? • How do the errors associated with the ODR measurement compare to the errors from propagating the synchrotron light monitor measurement in the arcs to the IP? • How fast can the ODR measurements be made? • What is the level of synchrotron radiation background at the ODR target? ODR for Hadron colliders

27. Next Steps • Design ODR setup in the Tevatron – E0 preferable. • Develop a collaboration with US labs and CERN • Present proposal to the LARP collaboration for funding a LARP task (April 2008) • Proceed with experiments • Develop ODR facility for the LHC • Determine potential for future machines: muon collider, ILC,… ODR for Hadron colliders