RD on noninvasive beam profile measurements Adam Jeff
R&D on non-invasive beam profile measurements Adam Jeff CERN & University of Liverpool
Motivation • Wire scanners, screens limited to pilot beams due to losses caused • Non-intercepting monitors needed for online beam size measurement • Techniques exist but will be pushed to the limit by small beam size • ~100 μm for FCC-hh, vertical size as low as 1. 2 μm for FCC-ee adam. jeff@cern. ch Synchrotron Radiation • Visible light imaging • Interferometry • X-ray imaging Gas-based techniques • Ionisation monitor • Gas fluorescence • Vertexing • Gas jet scanner Crossed Beams • Laser-wire • Electron-beam scanner
Motivation • Wire scanners, screens limited to pilot beams due to losses caused • Non-intercepting monitors needed for online beam size measurement • Techniques exist but will be pushed to the limit by small beam size • ~100 μm for FCC-hh, vertical size as low as 1. 2 μm for FCC-ee adam. jeff@cern. ch Synchrotron Radiation • Visible light imaging • Interferometry • X-ray imaging Gas-based techniques • Ionisation monitor • Gas fluorescence • Vertexing • Gas jet scanner Crossed Beams • Laser-wire • Electron-beam scanner
adam. jeff@cern. ch Synchrotron Radiation • Substantial amount of visible synchrotron light at all energies • At top energy, plenty of x-rays too
adam. jeff@cern. ch Synchrotron Radiation • Simplest option: imaging of visible SR • LHC experience shows we cannot achieve required resolution
adam. jeff@cern. ch Synchrotron Radiation • SR interferometry overcomes diffraction limit • Beam size measurement only Thanks to G. Trad, CERN
adam. jeff@cern. ch Synchrotron Radiation • Reduce diffraction by moving to shorter wavelengths • Many techniques from synchrotron light sources available Pinhole Camera Fresnel Zone Plate Compound Refractive Lens
adam. jeff@cern. ch Synchrotron Radiation • Need to separate SR from particle beam • Large bending radius means long distance (>100 m) dipole SR monitor beam SR fan
adam. jeff@cern. ch Synchrotron Radiation FCC-hh Injection Do. F Δx 3 m 850 μm Top Energy 0. 2 m 4 μm • Can get round this by using a dedicated undulator • LHC undulator would produce soft x-rays SR monitor
Motivation • Wire scanners, screens limited to pilot beams due to losses caused • Non-intercepting monitors needed for online beam size measurement • Techniques exist but will be pushed to the limit by small beam size • ~100 μm for FCC-hh, vertical size as low as 1. 2 μm for FCC-ee adam. jeff@cern. ch Synchrotron Radiation • Visible light imaging • Interferometry • X-ray imaging Gas-based techniques • Ionisation monitor • Gas fluorescence • Vertexing • Gas jet scanner Crossed Beams • Laser-wire • Electron-beam scanner
adam. jeff@cern. ch Gas Ionisation & Fluorescence Ionisation Profile Monitor Beam Fluorescence Monitor Thanks to P. Forck, GSI • Space charge effects distort profile measurement • Need superconducting magnet to constrain ions • Fast measurement if additional gas injected • Space charge not a problem if neutral excited line chosen • Resolution very challenging • Smaller cross-section • Higher pressure or long integration • Background due to ionisation / excitation by synchrotron radiation
adam. jeff@cern. ch Beam Gas Vertexing • New technique based on inelastic scattering between beam and rest gas • Several tracks are reconstructed for each event & vertex is located • Vertices are collected over many turns to image beam Scintillating-fiber detectors Gas volume Reduced aperture Thin end wall Thanks to P. Hopchev, CERN
adam. jeff@cern. ch Beam Gas Vertexing • Technique used successfully at LHCb for beam imaging • Dedicated instrument installed in LHC for testing during run 2 Thanks to P. Hopchev, CERN
adam. jeff@cern. ch Beam Gas Vertexing • Main requirements: • Vertex resolution smaller than the beam size • “Sufficient” beam-gas rate • Both should be fulfilled for FCC-hh. Vertex resolution too big for FCC-ee • Higher beam energy -> more forward tracks • In-vacuum detectors may be needed Gas target Sensor hit resolution Measurements per track Detector acceptance BGV demo @ LHC BGV @ FCC-hh Neon @ 6 x 10 -8 mbar Same or lower pressure ~ 70 micron Similar or better 4 At least 4 ~ 20 – 80 mrad polar angle over 1 m Smaller polar angles • Experience with LHC prototype and developments for HL-LHC will demonstrate feasibility Thanks to P. Hopchev, CERN
Gas Jet Scanner adam. jeff@cern. ch Thanks to M. Putignano, Cockcroft Inst. • Collimated ‘curtain’ gas jet can be used with ionisation or fluorescence • Test stand at the Cockcroft Institute shows high-vacuum compatibility
Generate a thin pencil jet and scan it through the beam Like a wire scanner but non-interceptive Readout by ion counting, fluorescence, bremsstrahlung, or beam losses Not affected by space charge as position given by gas jet Need a way to generate a thin jet… adam. jeff@cern. ch Gas Jet Scanner • • • ‘Atomic Sieve’ to focus neutral gas jet based on de Broglie wavelength • Will be tested at Cockcroft Institute this year
Motivation • Wire scanners, screens limited to pilot beams due to losses caused • Non-intercepting monitors needed for online beam size measurement • Techniques exist but will be pushed to the limit by small beam size • ~100 μm for FCC-hh, vertical size as low as 1. 2 μm for FCC-ee adam. jeff@cern. ch Synchrotron Radiation • Visible light imaging • Interferometry • X-ray imaging Gas-based techniques • Ionisation monitor • Gas fluorescence • Vertexing • Gas jet scanner Crossed Beams • Laser-wire • Electron-beam scanner
Laser-wire Scanner adam. jeff@cern. ch L. Nevay, RHUL • Scan laser beam and detect high-energy photons from inverse compton scattering • Proven method for measurement of very small electron beams • Proton cross-section is 6 orders of magnitude smaller • Need to separate photons from beam and distinguish from SR
adam. jeff@cern. ch Electron-Beam Scanner W. Blokland, ORNL • The ‘probe’ beam of electrons is deflected by the E-field of the main beam. The deflection depends on where the probe beam passes through the main beam. • Using a diagonal curtain of electrons allows the profile to be measured in a single shot. • For FCC-hh, resolution is challenging but not impossible • For FCC-ee, situation is more complicated due to short bunches
17 / 17 Conclusions adam. jeff@cern. ch Conclusions • Profile measurements at the FCC will be challenging due to the high beam power and small beam size • Synchrotron radiation will be useful – We can learn from the light source community – But solutions may not be directly portable due to the large bending radius • Other techniques such as beam gas vertexing and the gas jet scanner are promising, and will be tested soon at CERN and the Cockcroft Institute
Thank you for your Attention • Synchrotron Light at the LHC • • • Precision luminosity measurements at LHCb, LHCb collaboration, JINST 9 (2014) P 12005 • A Beam Gas Vertex Detector for Beam Size Measurement in the LHC, P. Hopchev et al. , Proc. IPAC (2014) Measurement of small transverse beam size using interferometry, T. Mitsuhashi, Proc. DIPAC (2001) • Gas Jet • X-ray imaging • • Design and performance of the upgraded LHC synchrotron light monitor, A. Goldblatt, E. Bravin, F. Roncarolo, G. Trad, Proc. IBIC (2013) Beam Gas Vertexing SR Interferometry • • • X-ray pinhole camera resolution and emittance measurement, C. Thomas, G. Rehm, I. Martin, Phys. Rev. ST Accel. Beams 13 (2010) • Beam Gas Ionisation & Fluorescence • Minimal invasive beam profile monitors for high intense hadron beams, P. Forck, Proc. IPAC (2010) Laser-wire • • A quantum gas jet for non-invasive beam profile measurement, A. Jeff, E. B. Holzer, T. Lefèvre, V. Tzoganis, C. P. Welsch, H. Zhang, Proc. IBIC (2014) Laserwire at the Accelerator Test Facility 2 with submicrometer resolution, L. J. Nevay et al. , Phys. Rev. ST Accel. Beams 17 (2014) E-beam • Electron scanner for SNS ring profile measurements, W. Blokland, S. Aleksandrov, S. Cousineau, D. Malyutin, S. Starostenko, Proc. DIPAC (2009)
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