Orbit Control at the SLS Storage Ring 26th Advanced ICFA Beam Dynamics Workshop on Nanometre-Size Colliding Beams (September 2-6, 2002, Lausanne) T. Schilcher Outline • Stability Requirements • Feedback Implementation 1 Slow Orbit Feedback • Results of Slow Orbit Feedback • Upgrade to Fast Orbit Feedback 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
SLS Parameters Energy: 2.4 GeV RF frequency: 500 MHz Circumference: 288 m Emittance (horizontal): 5.0 nm · rad Vertical Beamsize X 10 µ m (1% coupling) @ ID (short straights): Beta functions @ short straights: horizontal: 1.4 m vertical: 0.9 m Stability Requirements Source fluctuations < one order of magnitude below resolution of experimental stations angular stability: < 1 µ rad ∆Θ ! beam position stability: 1/10th of vertical beam size at ! location of insertion devices 1 1 µ m in vertical plane suppress oscillations up to 100 Hz by factor of 10 ! 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Feedback Strategy ! using all 72 BPMs and all 72 corrector magnets in each plane global orbit feedback based on SVD algorithm ! ! RF frequency as independent control parameter Slow Orbit Feedback BPM / SLS Corrector Storage Ring BPM / BPM / Station Corrector Corrector Station Station central processing unit: 100 Mbit/s BPM / BPM / calculate inverted Ethernet Corrector ! Corrector Station Station response matrix (SVD) beam dynamics BPM / read all BPM values BPM / ! Corrector Corrector server Station Station calculate correction ! set new corrector BPM / BPM / ! Corrector Corrector Station Station settings BPM / BPM / Corrector Corrector use control system BPM / Station ! Station Corrector Station network Fast Orbit Feedback BPM / SLS Corrector Storage Ring BPM / BPM / Station Corrector Corrector Station Station bpm 1 72 1 100 Mbit/s BPM / BPM / Ethernet Corrector Corrector Station Station A = -1 ! corr. beam dynamics BPM / BPM / Corrector 72 Corrector server Station Station 72x72 processing decentralized ! BPM / BPM / Corrector Corrector and integrated in the 12 Station Station BPM stations (6 BPMs BPM / BPM / 40 Mbyte/s Corrector Corrector point-to-point BPM / Station Station fibre optic links Corrector and 6 corrector magnets Station per station) 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Slow Orbit Feedback: Properties stroboscopic position readings with ! a rate of 3 Hz (BPM resolution < 0.5 µ m) BPM server sends data to feedback client ! with a rate of 2 Hz sliding average of BPM data over a ! predefined no. of successive samples (default: 3) correction calculated on TRACY server ! toggle correction between x & y plane ! full correction cycle < 3 s ( X 0.4 Hz ) ! running since Aug. 2001 ! 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Results of Slow Orbit Feedback Example: 3 days run, 13 Aug 2002 - 16 Aug 2002 beam current: 181 current [mA] 180 179 180 mA top-up ∆ I / I = 3.3 E 1 0 −3 178 177 0 14 28 42 56 70 84 time [h] top-up operation ! 1 thermal equilibrium of machine 1 nearly no drifts 1 no beam current dependencies of BPMs 1 constant heat load on experiments correct orbit to “golden orbit” ! - minimum coupling (beam based alignment) - requested local bumps at ID 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Global Orbit Stability Global RMS Values: 35 30 number of samples @ 0.4 Hz x (rms) [ µ m] 25 RF freq. 20 corrections 15 10 5 0 0 1 2 3 4 0 14 28 42 56 70 84 x (rms) [ µ m] time [h] 25 20 y (rms) [ µ m] number of samples @ 0.4 Hz 15 10 5 0 0 1 2 3 4 0 14 28 56 70 84 42 y (rms) [ µ m] time [h] 1 orbit globally stabilzed to micron level 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Global Horizontal Mean Position: 5 0 -5 -10 x mean [ µ m] -15 -20 -25 RF frequency corrections -30 -35 -40 -45 -50 0 14 28 56 70 84 42 time [h] RF frequency corrections: if path length changes correspond to > 5 Hz frequency changes � Energy Stability: G 2 E 10 -5 number of samples @ 0.4 Hz -4e-05 -3e-05 -2e-05 -1e-05 0 1e-05 2e-05 3e-05 4e-05 dp / p 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
RF Frequency Change: -1540 -1550 -1560 -1570 ∆ f [Hz] -1580 -1590 -1600 1 day 1 day -1610 -1620 -1630 0 14 28 42 56 70 84 time [h] ∆ f = 5 Hz 1 ∆ U Z 3 µ m (circumference) Outside Temperatures: 30 28 outside temperatures [deg C] 26 24 22 20 18 16 14 12 1 day 1 day 10 0 14 28 42 56 70 84 time [h] 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
RF BPM @ Insertion device 6S (protein crystallography beamline): x position: 15 σ = 1.04 µ m x 10 number of samples @ 0.4 Hz x position [ µ m] 5 0 -5 -10 -15 -4 -2 0 2 4 upstream BPM x position [ µ m] -20 0 14 28 42 56 70 84 time [h] y position: σ = 0.65 µ m 15 y 10 number of samples @ 0.4 Hz y position [ µ m] 5 0 -5 -10 -15 0 -4 -2 2 4 upstream BPM y position [ µ m] -20 0 14 28 42 56 70 84 time [h] downstream BPM horizontal: vertical: σ = 0.98 µ m σ = 0.64 µ m x y 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Angular Stability @ ID σ = 0.29 µ rad horizontal angle: ∆Θ number of samples @ 0.4 Hz -1.5 -1 -0.5 0 0.5 1 1.5 horizontal angle [ µ rad] σ = 0.19 µ rad vertical angle: ∆Θ number of samples @ 0.4 Hz -1.5 -1 -0.5 0 0.5 1 1.5 vertical angle [ µ rad] 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
X-BPM Results X-BPM @ Protein Crystallography Beamline ! start of X-BPM commissioning: ! middle of Aug. 2002 data from 3 days run: 9 Aug - 12 Aug 2002 ! -60 -65 y position [ µ m] -70 drift: X 1.7 µ m -75 ! -80 per day -85 -90 subtracting the ! -95 1 drift -100 0 8.6 17.2 25.8 34.4 1 time [h] horizontal: vertical: σ = 2.7 µ m σ = 1.5 µ m x y number of samples @ 0.4 Hz number of samples @ 0.4 Hz -10 -5 0 5 10 -10 -5 0 5 10 x position [ µ m] y position [ µ m] 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Fast Orbit Feedback Properties: update rate: 4 kHz ! BPM data exchange only between adjacent ! sectors over point-to-point fibre optic links (40 Mbytes/s) ( 1 reflecting the localized structure of the inverted response matrix) direct control of magnet power supplies ! (by-passing control system) Status: global BPM data exchange < 8 µ s ! implementing communication between ! beam dynamics server and individual BPM/feedback stations planned start of commissioning: Dec. 2002 ! (priority to multibunch feedback system) Important Prerequisite: reliable BPM data 1 “intelligent” BPM software which detects faulty data and disables BPM 1 already implemented for slow orbit feedback 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
Conclusion global orbit stabilized to 1 µ m in both ! planes with a rate of 0.4 Hz RF frequency control to compensate path ! length changes beam stability @ low beta insertion ! devices to (sub)micron level: position angle X 1.0 µ m X 0.3 µ rad horizontal X 0.7 µ m X 0.2 µ rad vertical thermally stable machine only needs ! feedback when - moving IDs - changing RF frequency fast feedback required in order to ! - compensate ID movements - suppress beam oscillations in the low frequency band (<40 Hz) - if necessary 26th Advanced ICFA Beam Dynamics Workshop ,Sep. 2 - 6, 2002 T. Schilcher
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