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Imaging the LHC beam

This study examines the application of synchrotron radiation for imaging and monitoring at the Large Hadron Collider (LHC) upgrade, focusing on beam separation techniques and radiation sources. Various aspects including magnet technology, energy deposition, and impact parameters are analyzed for optimizing imaging capabilities. The research discusses the characteristics of synchrotron radiation sources, diffraction radiation spectrum, and diffraction radiation layout at the LHC. By exploring diffraction radiation, the potential for precise beam monitoring and measurement of beam properties is highlighted. The study also investigates the feasibility of utilizing diffraction radiation for turn-by-turn and bunch-by-bunch monitoring at lower energies within the LHC upgrade framework.

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Imaging the LHC beam

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  1. Imaging the LHC beam Tanaji Sen Accelerator Division Prospects for the LHC upgrade • Synchrotron Radiation • Optical Diffraction Radiation December 13, 2006

  2. Early separation – D0 IP D1 Triplet Triplet D1 D0 D0 • Early separation dipoles D0 placed inside the detector • Beams collide with no crossing angle (D0 less than 3.75m from IP) or with a small crossing angle (D0 more than 3.75m from the IP). • Luminosity loss due to crossing angle much smaller • Issues • Integrating the dipoles into the detectors CMS and ATLAS • Energy deposition in the detectors • Impact of a few parasitics at small separations (< 4 σ) • Choice of magnet technology: NbTi or Nb3Sn (shorter)

  3. Usable spectrum • Quartz windows are transparent between 200 – 2500 nm. • CCD cameras operate in the range 200-1100 nm

  4. Synchrotron Radiation Sources • Long Magnet – bend angle θ>> 1/γ Characteristic λc = 4πρ/(3γ3) = 58nm for D0 dipole in LHC at 7 TeV; 3004nm for Tevatron dipole at 980 GeV • Short Magnet θ << 1/γ • Edge Radiation, λe = Le/(2γ2) < λc 1/γ Long Magnet θ/2 Short Magnet Edge Radiation

  5. Synchrotron Radiation spectrum • D0 dipole in the LHC with field 4 T-m. Θ=0.17mrad > 1/γ = 0.13mrad. So not a short dipole. • Critical frequency νc = 5.1x1015 Hz • Half the power is radiated at frequencies below νc and half above. • Shape of spectrum is universal, at other energies the curve is just shifted.

  6. Angular spectrum - body Radiation in the visible range has a large angular spread. Difficult to use for imaging. 400 nm

  7. Edge Radiation • Characteristic λc = Le/2γ2. If Le ~ 40mm, λc = 1nm (deep UV) • Radiation from the edges must not overlap, => θ > 2/γ • Extraction mirror should be 15σ from the beam, => B=12.6T for L = 15m. Too high a field and larger distances are unavailable. 15σ Beam L

  8. Diffraction Radiation - Layout CCD Filter Polarizer BDR Measured at KEK Phys. Rev Letters 90, 104801 (2003) 93, 244802 (2004) 2Φ FDR Target Proton beam p h Impact parameter Φ Target

  9. LHC - Placing the target • The impact parameter at 7 TeV, 1000 nm • Target should be clear of the beam • Close to the IP, • At 7 TeV, β*=0.25m, λ = 1000 nm, Target can be placed at s ≤ 19m from IP !!

  10. DR spectrum and photon yield • Characteristic λc = 4πh/γ • At h = 1.2mm, λc = 2021 nm • Spectrum at ω > 0.2 ωc • Photon yield/bunch/turn • At ω = 2 ωc or λ=1010 nm, ΔN = 1.81x 106 photons/bunch/turn

  11. Exploration of Diffraction Radiation • May allow turn by turn and bunch by bunch monitoring • Explore potential to measure: beam size, beam divergence, beam position (from polarization, angular distribution, …) • Prospects at lower energies: 450 GeV ≤ E ≤ 7 TeV • If no major obstacles, explore this as a new LARP instrumentation task (FNAL joint with ANL(?), LBL, …)

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