Wir schaffen Wissen – heute für morgenPaul Scherrer InstitutVolker Schlott, Matsamitsu Aiba, Michael Böge, Natalia Milas,Martin Rohrer, Angela Saa-Hernandez, Andreas Streun (PSI)Åke Andersson, Jonas Breulin (MaxLab)

Design and Expected Performance of the
New SLS Emittance Monitor
PSI, October 1, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Contents• Motivation – EU-Project TIARA WP-6 SVET
• Swiss Light Source – 1 pmrad Vertical Emittance• Measurement Principles – π-Polarization Method
Interferometric Method• New Monitor Design – New Features & Improvements• Critical Issues and Components• Status & Outlook
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Test Infrastructure and Accelerator Research Area
www.eu-tiara.eu

Work Package 6 “SVET”

Partially funded by the European Commission under the FP7-INFRASTRUCTURES-2010-1/
INFRA-2010-2.2.11 project TIARA (CNI-PP). Grant agreement no 261905.

SVET: SLS Vertical Emittance Tuning→ investigate ultra-low vertical emittance tuning and control in the regime of strong IBS→ relevance for damping rings of future linear colliders & for next generation light sources→ upgrade Swiss Light Source to enable R&D on ultra-low emittances

SVET Partners
PSICERN
INFN/LNF
Max-IV-Lab→ SLS coupling suppression and control→ CLIC damping ring design→ Super-B factory design→ MAX-IV emittance measurement and coupling control

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

SVET Activities
1. verification of low vertical emittancebeam size measurement: σyemittancemagnet optics control: βydesign of a high resolution beam size monitor at SLS (PSI and Max-Lab)

2. minimization of vertical emittancebeam-assisted SLS storage ring alignment and optics correction
tuning methods and automation
skew quadrupole corrections and orbit settings (PSI and INFN / LNF)

3. intra beam scattering simulations and measurements
emittance and energy spread increase at high currents
low energy (1.6 GeV) operation of SLS (PSI, CERN)
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Swiss Light Source – Some Key Parameters• Beam Energy• Circumference• Emittances2.4 GeV

horizontal
vertical

5.5 nm rad
1 … 7 pm rad• Coupling• Energy Spread• Beam Current• Life Time• Stability

0.02 % … 0.13 %288 m

0.09 %
400 mA (top-up operation)~ 3 – 10 h
< 1 µm (photon beam at front end)

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012SR User Facility with 19 Beam Lines (Status 2012)

Design and Expected Performance of the New SLS Emittance Monitor

Pre-Requisites and Tools for SLS Vertical Emittance Tuning
1. high beam stability as a pre-requisite
top-up operation → high thermal (long term) stability
precise BPMs:~ 100 nm rms (< 100 Hz)
fast orbit feedback

orbit control & short term stability

2. procedures & equipment for vertical emittance tuning
re-alignment (beam-assisted girder alignment) of storage ring
→ remote positioning of 48 girders in 5 DoF (eccentric cam shafts drives)
skew quadrupoles for coupling control (36 in case of SLS)
→ sextupoles with additional coils
high resolution beam size monitor→ π polarization method

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance MonitorProcedure for SLS Vertical Emittance Tuning
1. measurement and correction of BPM roll error→ avoid “fake” vertical dispersion readings (from 48 dispersive BPMs with ηhor ≠ 0)

2. realignment of magnet girder to remove main sources of vertical dispersion→ reduction of rms vertical correction kick from ~ 130 µrad to ~ 50 µrad

3. measurement & correction of linear optics→ model-based quadrupole corrections

4. measurement & correction of vertical dispersion and betatron coupling→ model-based skew quadrupole corrections (12 dispersive and 24 non-dispersive skew quads)

5. “random walk” optimization of vertical beam size
→ skew quadrupole corrections using beam size measurements from profile monitor
works in the background (small steps), overcomes measurement limitations and model deficiencies
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

SLS Vertical Emittance Optimization – Results
Iterative Minimization Procedure→ BPM roll error corrections→ beam-based girder alignment→ dispersion & coupling corrections→ beam size monitor tuning→ random walk optimization

Illustration of SLS Beam Size (short ID straight – 2σ)courtesy of A. Streun
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

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

Design and Expected Performance of the New SLS Emittance Monitor

SLS Vertical Emittance Optimization – Results• vertical beam size: 3.6 µm ± 0.6 µm• vertical emittance: 0.9 pm ± 0.4 pm• error estimate from beam sizeand β-function at monitor• dispersion not subtracted

Beam Size Display from SLS π-Polarization Monitor

Horizontal and Vertical Emittances of Storage Rings

existing () and planned ()Figure taken from:
R. Bartolini, Low Emittance Ring Design, ICFA Beam Dynamics
Newsletter, No. 57, Chapter 3.1, 2012 – and updated.

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Principle of the SLS Beam Size Monitor – The π-Polarization Method Å. Andersson, et al., Determination of Small Vertical Electron Beam Profile and Emittance at the Swiss Light Source, NIM-A 592 (2008) 437-446
SpectralFilter• imaging of vertically polarized SR in the visible / UV

2-D Electric Field Distribution (in image plane)• phase shift of π between two radiation lobes⎛ 2πx c ⎞Eπ ( x, y ) = Eπ 0 sinc ⎜, x ⎟⎝ λ p ⎠→ destructive interference in the mid plane→ Iy=0 = 0 in FBSF (filament beam spread function)+∞⎛ 2πp ⎞⎛ 1 λ123 2 ⎞× ∫ (1+ ζ 2 ) ζ K1 3 ⎜ c (1+ ζ) ⎟ sin ⎜, yζ⎟ dζ⎝⎠2λλγp⎝⎠0• finite vertical beam size → Iy=0 > 0 in FBSF
• modeling by SRW* (Synchrotron Radiation Workshop)

2-D Intensity Distribution (in image plane)€ O. Chubar & P. Elleaume, Accurate and Efficient Computation ofSynchrotron Radiation in the Near Field Region, EPAC 1998
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

€cos (ψ ) −1
Iπ ( x, y ) ~ sinc ( x ) ×ψ
22with ψ =2π θ yλ

Design and Expected Performance of the New SLS Emittance Monitor

Comparison of the “Old” and “New” SLS Beam Size Monitor• operating wavelength: 403 / 364 / 325 nm• opening angle:
7 mradH x 9 mrad V• finger absorber to block main SR intensity• imaging by fused silica lens• magnifications:• surface quality of optics:

0.854 / 0.841 / 0.820< 30 nm (λ/20 @ 633 nm)• operating wavelength:variable (266 nm)• opening angle:
7 mradH x 9 mrad V• finger absorber to block main SR intensity• imaging by toroidal mirror• magnification:• surface quality of optics:

1.453< 20 nm (λ/30 @ 633 nm)

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Comparison of the “Old” and “New” SLS Beam Size Monitor• operating wavelength: 403 / 364 / 325 nm• opening angle:
7 mradH x 9 mrad V• finger absorber to block main SR intensity• imaging by fused silica lens• magnifications:• surface quality of optics:

0.854 / 0.841 / 0.820< 30 nm (λ/20 @ 633 nm)• operating wavelength:variable (266 nm)• opening angle:
7 mradH x 9 mrad V• finger absorber to block main SR intensity• imaging by toroidal mirror• magnification:• surface quality of optics:

1.453< 20 nm (λ/30 @ 633 nm)• π-polarization or interferometric method selectableVolker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor“New” SLS Beam Size Monitor – 2nd Method: SR Interferometry
 T. Mitsuhashi, Spatial Coherency of the SR at the Visible Light Region and its Application forElectron Beam Profile Measurement, Proc. PAC 1997, Vancouver, p. 766

spectral filter
λ0 ± Δλpolarizer

Y0D2aR0R• double slit Michelson interferometer adapted for beam size measurements by T. Mitsuhashi (see WEIC02)• van Citert-Zernike’s theorem relates transverse distribution f(y) via FFT with spatial coherence γ(y)Intensity of Interference Pattern→ spatial coherence€⎡⎛ π a χ( D) ⎞⎤ ⎡⎛ 2π D ⎛ y 0⎞⎞ ⎤
I ( y 0 ,D) = ( I1 + I2 ) ⎢sinc ⎜
y 0 ⎟⎥ ⋅ ⎢1+ γ cos⎜⋅ ⎜ +ψ ⎟⎟ ⎥⎠⎠ ⎦⎝ λ ⎝ R⎝ λ R⎠⎦ ⎣⎣⎛ 2 I ⋅ I ⎞ ⎛ I − I ⎞λ R 1 ⎛ 1 ⎞
1 2⎟⎟⋅ ⎜ max min ⎟ provides rms beam size σ =γ = ⎜⎜ln ⎜ ⎟
I+II+IπD2⎝ γ ⎠⎝⎠⎝ 1 2 ⎠ max minVolker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012€€

Design and Expected Performance of the New SLS Emittance Monitor

The “New” SLS Beam Size Monitor – Beam Line X08DA
calibration & alignment

Main Features of the “New” SLS Beam Size Monitor• X08-DA allows for longer beam line

→ optics table fully accessible outside of accelerator bunker• higher magnification ratio (M = -1.45)→ increase of measurement precision• toroidal mirror as focusing element→ free selection of SR wavelength without shift of image plane→ shorter wavelength increases resolution• π-polarization & interferometric method → matched operating ranges (nominal and high resolution)→ cross-checking of results• alignment & calibration set-up
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

→ online inspection of monitor at 266 nm and 532 nm

Design and Expected Performance of the New SLS Emittance Monitor

The “New” SLS Beam Size Monitor – Critical Elements and Issues I
Focusing Element – Toroidal Mirror• S1 = 5.146 m• S2 = 7.459 m• RX = 6.592 m• RZ = 5.627 m• Θ 22.5°→ M = - 1.453→ FX = FZ = 3.045 m• Material: SiC (silicon carbide), Al-coated (UV enhanced)• Surface Quality:
slope error 0.2 arcsec
roughness 21 nm pp (λ/30) , < 4 nm rms
wavinesshorizontal, vertical, radial

Modelling of Toroidal Mirror Surface Quality

horizontal stripes→ asymmetry

vertical & radialstripes→ acceptableVolker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

The “New” SLS Beam Size Monitor – Critical Elements and Issues II
Toroidal Mirror – Offsets & Misalignments• horizontal offset DX• vertical offset DY

Influence of Tilts (TX, TY) and Axis Rotation
horizontal tilt TX
symmetric broadening andand washing out of peak-to-valley patternrotation around mirror axis R
and vertical tilt TY
asymmetric washing out ofpeak-to-valley pattern for R & TY
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012→ not critical within ± 50 µm

Design and Expected Performance of the New SLS Emittance Monitor

The “New” SLS Beam Size Monitor – Calibration & Alignment
 mode images from: Meyrath et al., Opt. Express, Vol. 13, Issue 8, pp. 2843-2851 (2005)
polarizer
remotemirror-1

Δφ = 0
CryLas FQSS 266-Q Laser

266 nm & 532 nm
Δφ = π	pinholes
100 - 5 µm

waveplates formode transformation
TEM00 → TEM01

to π-polarization
monitor beam line
remotemirror-2• CryLas FQSS 266-Q Laser…:

λ1 = 266 nm, λ2 = 532 nm, vertically polarized (100:1), TEM00• pinholes as virtual source…:

diameters of 100 µm, 50 µm, 25 µm, 15 µm, 10 µm, 5 µm, 1 µm

• “mode transformation”“polarization rotation”…:

λ/2 waveplates at 0° (upper half) and 90° (lower half)• remote controlled mirrors…:

for beam transfer into π-polarization beam size monitor

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

The “New” SLS Beam Size Monitor – Expected Performanceπ-Polarization Branch – Emittance Resolution

Interferometer Branch – Emittance Resolution25 mm obstacle size

π-Polarization Branch – Resolution vs Wavelength

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Interferometer Branch – Resolution vs Obstacle Size

Design and Expected Performance of the New SLS Emittance Monitor

The “New” SLS Beam Size Monitor – Expected Performance
Comparison: π-Polarization Branch – Interferometer Branch• improved resolution→~ 4 µm (old monitor) to ~ 2 µm (new monitor)• two measurement methods→→

π-polarization for nominal SLS operationinterferometer for low emittance studies• calibration & alignment path→online check of monitor performance

Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Summary and Outlook• methods for emittance tuning established at SLS (within TIARA-SVET collaboration)→ lowest vertical emittance of 0.9 ± 0.4 pmrad• design of “new” high resolution beam size monitor at SLS→ application of π-polarization and interferometeric methods→ overlapping sensitivity ranges for nominal SLS operation and low emittance studies→ mirror optics (toroidal focusing mirror) provides free selection of SR wavelength→ sensitivity study using SRW provides specifications for optical elements→ calibration and alignment branch allows for online monitor performance check→ expected measurements resolution for vertical beam height ~ 2 µm

• next steps…:→ installation of “new” monitor in SLS X08DA beam line in January 2013
→ further εy minimization by mid of 2013 (towards SLS quantum emittance limit of 0.2 pmrad)→ automated coupling feedback using “new” beam size monitor in 2013
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012

Design and Expected Performance of the New SLS Emittance Monitor

Acknowledgementsmany thanks to…:
→ Jakob Ehrat and PSI mechanical engineering for construction & fabrication→ Albert Kammerer, Markus Baldinger & Rolf Wullschleger for installation→ Pavel Chevtsov & Colin Higgs for control system interfacing & support→ Helge Brands for CCD read-out and image processing→ Christian Lüscher & Stefan Speckert for safety & interlock systms (EPS & MIS)
→ Nazareno Gaiffi & the SLS vacuum group for UHV & installation support→ Elmar Zehnder & Beat Sommer for cabling & electrical installations→ Peter Oggenfuss & Roger Sommer for SLS floor coordination→ Tino Höwler & the alignment group for alignment of all components→ many more for their support and fruitful discussions→ the audience for their attention, interest and patience
Volker Schlott, IBIC-2012, Tsukuba, October 2nd, 2012