Performance of the New Emittance Monitor at SLS of the New Emittance Monitor at SLS . ... TIARA - PP Final Meeting ... TIARA-REP-WP6-2012-015. 3

Performance of the New Emittance Monitor at SLS

Jonas Breunlin, Åke Andersson (MAX IV Laboratory) Angela Saa-Hernandez, Masamitsu Aiba, Michael Böge, Natalia Milas, Martin Rohrer, Volker Schlott , Andreas Streun (PSI)

TIARA - PP Final Meeting – STFC Daresbury Laboratory – Nov 26th 2013

• Introduction and motivation

• Diagnostic beamline design

• Working principle

• Theoretical studies

• Beam size mesurement results

• Work ongoing

Jonas Breunlin – TIARA - PP Final Meeting – Nov 26th 2013

Outline

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Introduction

Limited by old monitor resolution!

Old monitor, commissioned in 2006 Å. Andersson et al., Determination of a small vertical electron beam profile and emittance at the Swiss Light Source, NIM-A 591 (2008) 437-446

– Estimations on beam size resolution suggested difficulties to measure 1 pm*rad vert. emittance – Modification discarded: monitor is integrated in machine diagnostics! Decision for a new monitor of similar design

• Low vertical emittance campaign in 2012

M. Aiba et al., Ultra Low Vertical Emittance at SLS Through Systematic and Random Optimization, NIM-A 694 (2012) 133-139

– Vertical beam size: 3.6 ± 0.6 µm – Vertical emittance: 0.9 ± 0.4 pm

• Apparent limitations of the old monitor

– Optical magnification (0.9) and wavelength (minimum 364 nm) New monitor, practicle advantages (amongst others)

– Optical magnification (1.8 to 2.0, depending on focusing element and wavelength) – Short wavelength (down to 266 nm) – Obstacles (complementary method, resembling an interference method) – Accessable experimental area

N. Milas et al., Specifications for the new SLS beam size monitor: Deliverable 6.2, TIARA-REP-WP6-2012-015

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Choice of focusing element: • Toroidal mirror (focal length is wavelength-independent, allowing broader bandwidths, at the

expense of a higher price and worse surface quality compared to…) • Spherical lens (presented measurements are done with this setup!) • Spherical mirror (discarded because of unpractical reflection angle needed to avoid aberrations) Optical component alignment with lasers Deviation from the optical axis of the lens < 0.5 mrad Optical hutch: access during machine operation


Beamline design

Example: Lens λ = 325 nm; S1 = 5.336 m; S2 = 10.073 m; M = 1.888

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Beamline design

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Imaging of synchrotron radiation (SR) from bending magnet in vis-UV • Focusing element (lens, mirror) and CCD camera in the image plane

π-polarized SR • Characteristic angular intensity distribution: lobes above and below the bending plane with π phase shift

Theoretical calculations with the ‚Synchrotron Radiation Workshop‘ (SRW) • Filament beam spread function (FBSF): image characteristics of a point-like bunch

Using π-polarized SR : the image has zero intensity in the mid-plane! • Measured beam profile: FBSF convolved with the electron beam profile • Ratio of intensity in mid-plane vs. side peaks is sensitive to the electron beam size


Working principle

𝐼𝑝

𝐼𝑣

O. Chubar, P. Elleaume, "Accurate And Efficient Computation Of Synchrotron Radiation In The Near Field Region", proc. of the EPAC98 Conference, 22-26 June 1998, p.1177-1179.

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valley-peak ratio: 𝐼𝑣𝐼𝑝


Theoretical studies Wavelength • Shorter wavelength: less diffraction dominated Interference method: introduce centered obstacle • 15, 20 and 25 mm (1 mm ≈ 0.2 mrad) • Complementary method • Potential to an increased resolution

Off-center obstacle (vertically displaced) • FBSF shows finite intensity in the mid-plane • May be advantageous for small beam sizes!

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σ𝑦 = 3.7 µm → ε𝑦 = 1 pm

Emittance monitor studies in September 2013 • Achieved vertical beam size: σ𝑦 = 4.8 ± 0.5 µm (without dedicated vertical emittance tuning shift)

Corresponding vertical emittance: ε𝑦 = 1.7 ± 0.4 pm

• Beta-function measurements ( by quadrupole strength variation method) β𝑥 = 0.481 ± 0.008 m ; β𝑦 = 13.41 ± 0.05 m

• Dispersion at the observation point: (measurement RF frequency scan, beam displacement measured with monitor)

η𝑥 = 27.2 ± 0.4 mm ; η𝑦 = −1.0 ± 0.2 mm Very low vertical dispersion -> negligible effect on derived emittance ->


Results

σ𝑦2 = ε𝑦β𝑦 + η𝑦2σδ2

ε𝑦 ≈σ𝑦2

β𝑦

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Results: π-pol. September 2013 Beam size measurements comparedy to SRW calculations π-polarized SR λ = 325 nm no intereference obstacle

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Results: π-pol., 20 mm obstacle

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September 2013 Beam size measurements comparedy to SRW calculations π-polarized SR λ = 325 nm 20 mm intereference obstacle

Vertical obstacle position strongly influences the mid-plane intensity! • Mid-plane intensity is minimized for centered obstacle • Scanning the obstacle: position alignment with high precision

Off-center obstacle measurements increase the distance to camera background -> chance to measure smaller beam size


Results: π-pol., 15 mm obstacle, vertically displaced

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Measurements and SRW calculations: 15 mm obstacle, centered 15 mm obstacle, displaced by 4.42 mm

• „Camera odyssey 266 nm“ – 1st measurements with old camera at 266 nm, unsatisfactory Measured images show unexplained deviations from theory New camera acquired

• Spots on the exit windows

– Old and new beam size monitor – Unexplained (UV-induced crystalization of Fused Silica?) – For now: change the light path through the exit window time to time


Work ongoing:

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We achieved: • Monitor beam line commissioning with lens • Measured beam with σ𝑦 = 4.8 ± 0.5 µm → ε𝑦 = 1.7 ± 0.4 pm • Beam size measurements with complementary methods in good agreement • Measured and simulated vertical beam profiles in good agreement Estimation on resolvable emittance under present monitor condition: σ𝑦 = 3.0 µm → ε𝑦 = 0.6 … 0.7 pm On the way: • Next monitor beamline studies at low ε𝑦 on Dec. 3rd • Systematic studies on monitor resolution • New UV camera for 266 nm • Toroidal mirror will be installed beginning of next year


Summary

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Documents

Performance of the New Emittance Monitor at SLS of the New Emittance Monitor at SLS . ... TIARA - PP Final Meeting ... TIARA-REP-WP6-2012-015. 3