R&D on non-invasive beam profile measurements Adam Jeff CERN & University of Liverpool

Motivation Wire scanners, screens limited to pilot beams due to material damage and 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 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 1

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 2 Motivation Wire scanners, screens limited to pilot beams due to material damage and 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

Synchrotron Radiation Substantial amount of visible synchrotron light at all energies At top energy, plenty of x-rays too Synchrotron Radiation spectra for FCC-hh dipoles 3

Synchrotron Radiation Simplest option: imaging of visible SR LHC experience shows we cannot achieve required resolution 4

Synchrotron Radiation SR interferometry overcomes diffraction limit Beam size measurement only Thanks to G. Trad, CERN 5

Synchrotron Radiation Reduce diffraction by moving to shorter wavelengths Many techniques from synchrotron light sources available Pinhole CameraFresnel Zone Plate Compound Refractive Lens 6

Synchrotron Radiation Need to separate SR from particle beam Large bending radius means long distance (>100m) dipole beam SR fan SR monitor 7

Synchrotron Radiation FCC-hhDoFΔxΔx Injection3 m850 μm Top Energy0.2 m4 μm Can get round this by using a dedicated undulator LHC undulator would produce soft x-rays SR monitor 8

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 9 Motivation Wire scanners, screens limited to pilot beams due to material damage and 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

Gas Ionisation & Fluorescence Background due to ionisation / excitation by synchrotron radiation 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 Thanks to P. Forck, GSI Ionisation Profile MonitorBeam Fluorescence Monitor 10

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 Thanks to P. Hopchev, CERN Scintillating-fiber detectors Reduced aperture Thin end wall Gas volume 11

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 12

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 Thanks to P. Hopchev, CERN Experience with LHC prototype and developments for HL-LHC will demonstrate feasibility BGV FCC-hh Gas 6 x 10-8 mbarSame or lower pressure Sensor hit resolution~ 70 micronSimilar or better Measurements per track4At least 4 Detector acceptance ~ 20 – 80 mrad polar angle over 1 m Smaller polar angles 13

Gas Jet Scanner Collimated ‘curtain’ gas jet can be used with ionisation or fluorescence Test stand at the Cockcroft Institute shows high-vacuum compatibility Thanks to M. Putignano, Cockcroft Inst. 14

Gas Jet Scanner ‘Atomic Sieve’ to focus neutral gas jet based on de Broglie wavelength Will be tested at Cockcroft Institute this year 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… 15

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 16 Motivation Wire scanners, screens limited to pilot beams due to material damage and 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

Laser-wire Scanner 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 Could detect decelerated electrons instead 17

W. Blokland, ORNL Electron-Beam Scanner 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 18 Accelerator beam Probe beam

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 – Opportunity for interested collaborators to study this option for FCC 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 Conclusions 19

Thank you for your Attention Synchrotron Light at the LHC Design and performance of the upgraded LHC synchrotron light monitor, A. Goldblatt, E. Bravin, F. Roncarolo, G. Trad, Proc. IBIC (2013) SR Interferometry Measurement of small transverse beam size using interferometry, T. Mitsuhashi, Proc. DIPAC (2001) X-ray imaging Beam diagnostics with synchrotron radiation in light sources, S. Takano, Proc. IPAC (2010) 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) The first experience with LHC Beam Gas Ionisation Monitor, M. Sapinski et al., Proc. IBIC (2012) Beam Gas Vertexing Precision luminosity measurements at LHCb, LHCb collaboration, JINST 9 (2014) P12005 A Beam Gas Vertex Detector for Beam Size Measurement in the LHC, P. Hopchev et al., Proc. IPAC (2014) Gas Jet A non-invasive beam profile monitor for charged particle beams, V. Tzoganis, C. Welsch, Appl. Phys. Lett 104 (2014) 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) Laser-wire Laserwire at the Accelerator Test Facility 2 with submicrometer resolution, L. J. Nevay et al., Phys. Rev. ST Accel. Beams 17 (2014) E-beam scanner Electron scanner for SNS ring profile measurements, W. Blokland, S. Aleksandrov, S. Cousineau, D. Malyutin, S. Starostenko, Proc. DIPAC (2009)