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Imaging the LHC beam

Imaging the LHC beam. Tanaji Sen Accelerator Division. Prospects for the LHC upgrade Synchrotron Radiation Optical Diffraction Radiation. December 13, 2006. Early separation – D0. IP. D1. Triplet. Triplet. D1. D0. D0. Early separation dipoles D0 placed inside the detector

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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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