R&D on non-invasive beam profile measurements

Adam JeffCERN & University of Liverpool

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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

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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 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

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• Substantial amount of visible synchrotron light at all energies• At top energy, plenty of x-rays too

Synchrotron Radiation spectra for FCC-hh dipoles

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• Simplest option: imaging of visible SR• LHC experience shows we cannot

achieve required resolution

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• SR interferometry overcomes diffraction limit• Beam size measurement only

Thanks to G. Trad, CERN

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• Reduce diffraction by moving to shorter wavelengths• Many techniques from synchrotron light sources available

Pinhole Camera Fresnel Zone Plate

Compound Refractive Lens

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S

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tion • Need to separate SR from particle beam

• Large bending radius means long distance (>100m)

dipole

beam

SR fan

SR monitor

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𝐷𝑜𝐹 ≈ 𝜌𝛾

∆ 𝑥 ≈ 𝜌𝛾 21

𝛾

1𝛾

FCC-hh DoF Δx

Injection 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

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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 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

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• 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 Monitor Beam Fluorescence Monitor

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• 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

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• Technique used successfully at LHCb for beam imaging• Dedicated instrument installed in LHC for testing during run 2

Thanks to P. Hopchev, CERN

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• 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 demo @ LHC BGV @ FCC-hhGas target Neon @ 6 x 10-8 mbar Same or lower pressure

Sensor hit resolution ~ 70 micron Similar or better

Measurements per track 4 At least 4

Detector acceptance~ 20 – 80 mrad polar angle

over 1 m Smaller polar angles

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s Jet

Sca

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• 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.

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• ‘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…

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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 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

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Lase

r-wire

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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

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W. Blokland, ORNL

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• 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

Accelerator beam

Probe beam

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• 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

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)