Low vertical emittance at the SLS (update December 2011 – October 2012) A. Saa Hernandez on behalf of the TIARA WP6 collaboration ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 Outline Summary of the project status Motivation, Equipment, Procedures and Results This year activities Design and expected performance of the “New” Beam Size Monitor Maintenance of the “Old” Beam Size Monitor Low energy IBS measurements at SLS Outlook ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

SLS Vertical Emittance Tuning (SVET) 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 “The main objective of SVET is to upgrade the Swiss Light Source (SLS) at PSI to enable R&D on ultra-low emittances. [...] SLS will – after this upgrade – be an R&D infrastructure suitable to investigate ultra-low vertical emittance tuning and control, in particular also in the regime of strong IBS. This is relevant for damping rings of future linear colliders and for next generation light sources.” Activities: 1. minimization of vertical emittance: (PSI and INFN/LNF) storage ring alignment, optics correction & tuning methods and automation 2. measurement of low vertical emittance: (PSI and Max-Lab) design & construction of a high resolution beam size monitor 3. intra beam scattering (IBS) studies: (PSI and CERN) simulations and measurements of emittance and energy spread increase at high currents ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

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 skew quadrupoles for coupling control (36 in case of SLS) → sextupoles with additional coils high resolution beam size monitor → π-polarization method ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 Principle of the 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 imaging of vertically polarized SR in the visible/UV phase shift of π between two radiation lobes → destructive interference in the mid plane → Iy=0 = 0 for point-like beam → Iy=0 > 0 for beam with finite vertical beam size look-up table for beam size determination from SRW  O. Chubar & P. Elleaume, Accurate and Efficient Computation of Synchrotron Radiation in the Near Field Region, EPAC 1998 ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Procedure for SLS Vertical Emittance Tuning 1. measurement and correction of BPM roll error → avoid “fake” vertical dispersion readings (from 48 dispersive BPMs with hhor ≠ 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 vertical dispersion and betatron coupling → model-based skew quadrupole corrections (12 dispersive and 24 non-dispersive skew quads) 4. “random walk” optimization of vertical beam size (NEW!) → skew quadrupole corrections using beam size measurements from profile monitor works in the background (small steps), overcomes measurement limitations and model deficiencies ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Random walk optimization of vertical beam size Model-independent correction Target function of the optimization is the measured vertical beam size The optimum solution is within easy “walking-distance” after systematic correction Potential of online optimization, i.e. keeping small emittance during the operation  M. Aiba, et al., Ultra Low Vertical Emittance at SLS Through Systematic and Random Optimization, NIM-A 694 (2012) 133-139 ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 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 ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 SLS Vertical Emittance Optimization – Results ESLS 2011 (results March 2011) ESLS 2012 (results December 2011) vertical beam size: 5.0 ± 0.5 µm 3.6 ± 0.6 µm vertical emittance: 1.9 ± 0.4 pm 0.9 ± 0.4 pm error estimate from beam size and β-function at monitor dispersion not subtracted Limited by beam size monitor resolution! Horizontal and Vertical Emittances of Storage Rings Beam Size display from SLS π-polarization monitor existing () and planned () Figure taken from: R. Bartolini, Low Emittance Ring Design, ICFA Beam Dynamics Newsletter, No. 57, Chapter 3.1, 2012 – and updated. ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Main Features of the “New” SLS Beam Size Monitor calibration & alignment X08-DA allows for longer beam line → optics table fully accessible outside of accelerator tunnel 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 → online inspection of monitor at 266 nm and 532 nm Main Features of the “New” SLS Beam Size Monitor ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 Expected performance π-Polarization Method – Emittance Resolution Interferometer Method – Emittance Resolution 25 mm obstacle width π -Polarization Method – Resolution vs Wavelength Interferometer Method – Resolution vs Obstacle Width ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 Expected performance π-Polarization Method vs. Interferometer Method improved resolution → ~ 4 μm (old monitor) to < 2 μm (new monitor) two measurement methods → π-polarization for nominal SLS operation → interferometer for low emittance studies calibration & alignment path → online check of monitor performance ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Critical issues: misalignments Toroidal mirror used for imaging → peak/valley ratio extremely sensitive to misalignments SRW simulations used to define constraints on mechanical alignment and for guidance during commissioning Offsets horizontal offset Dx vertical offset Dy → not critical within ± 50 μm Tilts and Axis Rotation horizontal tilt Tx symmetric broadening and and washing out of peak-to-valley pattern rotation around mirror axis R and vertical tilt Ty asymmetric washing out of peak-to-valley pattern for R & Ty ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Critical issues: surface quality Toroidal mirror specifications Surface errors modifies path length → modeled to set specifications of optical elements Model principle  M. Sanchez del Rio and A. Marcelli, Waviness effects in ray-tracing of real optical surfaces, NIM-A 319 (1992) + L Toroidal mirror specifications Slope error 0.2 arcsec Roughness 21 nm p-v (λ/30), <4 nm RMS Waviness pattern vertical (also radial) ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Modeling of interference of partially coherent light Calibration of measurements with numerical simulations from SRW + analytical model Interference of partially-coherent light is modulated, Ipeak/Ivalley varies as a function of the source size (e- beam) b θ ~size of partially-coherent light source w a ~aperture size and shape ~interference of light from 2 apertures s  B. J. Thompson and E. Wolf, Two-Beam interference with partially coherent light, Journal of the optical society of America 47 (1957) Preliminar! ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Maintenance of the old monitor: X-ray branch Replace exit window: aluminium - very low transmittance at low energy (1.6 GeV) diamond + kapton (100 μm) - kapton burns → vacuum problems diamond + diamond Good measurements for beam sizes ≥ 10 μm ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Maintenance of the old monitor: Visible/UV branch Replace second mirror and gimbal mount - broken Replace exit window fused silica - UV damaged sapphire - birrefringent = polarization changes fused silica Replace lens - UV damaged 30 % ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

Low energy IBS measurements at SLS SLS top-up mode at 1.6 GeV, for measurements of intra-beam scattering Not trivial procedure, scaling down parameters not enough → highly non-linear magnet behavior Setting booster with flat top at 1.6 GeV → still some non-reproducible problems Results from intra-beam scattering measurements: Beam size measurements (blue squares) and IBS expectations (based on CIMP formalism) for different zero vertical emittances and bunch lengths (solid lines)  F. Antoniou et al, Optics design optimization for IBS dominated beams, HB 2012 ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 Summary and Outlook methods for emittance tuning established at SLS → lowest vertical emittance of 0.9 ± 0.4 pmrad design of “new” high resolution beam size monitor at SLS → application of π-polarization and interferometric methods with 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 → expected measurements resolution for vertical beam height < 2 mm maintenance of old monitor; some difficulties most probably solved promising results on IBS measurements; new data to be analyzed next steps…: → installation of “new” monitor in SLS X08DA beamline in January 2013 → further emittance minimization until mid of 2013 (SLS quantum emittance limit at 0.2 pmrad) ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012

ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012 Thank you! ESLS Workshop, Helmholtz Zentrum Berlin, 19 - 20 November 2012