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Non-invasive Measurements of Diffraction Radiation from Hadron Colliders

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27 diapositives · 420 Views · Aug 07, 2014

This document discusses the diagnostics capability brought by Diffraction Radiation (DR) when charged particles pass near conducting targets in hadron colliders. It details the initial theory and advancements from the 1960s to practical applications seen from 1995 onwards, focusing on key parameters such as impact parameter, beam energy, and wavelength of emitted radiation. Key potential observables include intensity measurements, beam size, position, and divergence, with recent experimental findings from KEK, APS, and other laboratories showcasing its feasibility and precision in beam diagnostics.

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Non-invasive Measurements of Diffraction Radiation from Hadron Colliders
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  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