Non-invasive profile monitors for energy-frontier machines

Adam JeffCERN & University of Liverpool

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Motivation

• Beam profile measurements are crucial for understanding new machines• 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…

Future challenges

• Future Circular Collider

• CLIC drive beam• High-Lumi LHC

Imaging techniques

• Synchrotron radiation

• Gas ionisation & fluorescence

• Vertexing

Scanning techniques

• Laser-wire• Electron-beam

scanner• Gas jet scanner

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Motivation

• Beam profile measurements are crucial for understanding new machines• 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…

Future challenges

• Future Circular Collider

• CLIC drive beam• High-Lumi LHC

Imaging techniques

• Synchrotron radiation

• Gas ionisation & fluorescence

• Vertexing

Scanning techniques

• Laser-wire• Electron-beam

scanner• Gas jet scanner

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ture

Circ

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Future Circular Collider• Proton beams at up to 100 TeV and leptons at Top & Higgs energies• Synchrotron with 100 km circumference, field strength 2xLHC dipoles• Challenges: High stored energy, low loss tolerance, small beam size…

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Beam

CLIC Drive Beam• Two-beam acceleration scheme demonstrated at CTF3

2.4 GeV

1.5 TeV

CLIC• Two-beam acceleration scheme demonstrated at CTF3• High intensity in drive beam: 100 A peak current• Requires non-intercepting profile measurement

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High-Lumi LHC• Halo particles become important• Needs high-dynamic-range profile measurement• Hollow electron lenses for halo cleaning – need dedicated diagnostics

~4mm

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Motivation

• Beam profile measurements are crucial for understanding new machines• 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…

Future challenges

• Future Circular Collider

• CLIC drive beam• High-Lumi LHC

Imaging techniques

• Synchrotron radiation

• Gas ionisation & fluorescence

• Vertexing

Scanning techniques

• Laser-wire• Electron-beam

scanner• Gas jet scanner

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• FCC would produce lots of visible synchrotron light at all energies, even with protons

• At top energy, plenty of x-rays too

Synchrotron Radiation spectra for protons in FCC dipoles

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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

ynch

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adia

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

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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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• Background due to ionisation / excitation by synchrotron radiation

• Space charge effects distort profile measurement• Need strong magnet to

constrain ions• Fast measurement if additional

gas injected

• Space charge not a problem if neutral excited line chosen

• ‘Simple’ installation• Smaller cross-section

• Higher pressure or long integration

Thanks to P. Forck, GSI

Ionisation Profile Monitor Beam Fluorescence Monitor

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• Injection of a curtain-like gas jet through the beam pipe allows beam cross-section to be imaged

• Pressure is locally much higher -> stronger, faster signal• Jet can be collected on opposite side of beam pipe – relatively little

leakage to vacuum system.• Gas jet should be collimated, homogeneous and as thin as possible.

Details in next talk!

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Be

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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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Motivation

• Beam profile measurements are crucial for understanding new machines• 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…

Future challenges

• Future Circular Collider

• CLIC drive beam• High-Lumi LHC

Imaging techniques

• Synchrotron radiation

• Gas ionisation & fluorescence

• Vertexing

Scanning techniques

• Laser-wire• Electron-beam

scanner• Gas jet scanner

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Lase

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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

adam

.jeff@

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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.

• Has been demonstrated for (quasi-)DC beams – analysis more complicated with short bunches.

Accelerator beam

Probe beam

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• ‘Atomic Sieve’ to focus neutral gas jet based on de Broglie wavelength• Now being tested at Cockcroft Institute

• 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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• Profile measurements at future energy-frontier machines will be challenging due to high intensity & small beam size.

• Exotic animals like electron lenses need unique solutions.

• Existing non-invasive techniques will be useful but cannot answer all the challenges– Synchrotron radiation difficult with v. large radius– Beam-gas ionisation limited by space charge

• Novel techniques such as beam gas vertexing and the gas jet scanner are promising, and will be tested soon at CERN and the Cockcroft Institute respectively.

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)

• X-ray imaging

• Beam diagnostics with synchrotron radiation in light sources, S. Takano, Proc. IPAC (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

• A Beam Gas Vertex Detector for Beam Size Measurement in the LHC, P. Hopchev et al., Proc. IPAC (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)

• Gas Jet scanner

• 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)

• Other

• La dieta del cucurucho, A. Benot Morel (2015)