Orbit Studies during ALBA Commissioning · 0 1 2 3 Horizontal [mm] mean rms max 0 1 2 3 Vertical 13...
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M. Mu˜ noz ∗ , Z. Mart´ ı, D. Einfeld, G. Benedetti, CELLS-ALBA, Bellaterra, Spain Abstract The 3rd generation light source ALBA is in the com- missioning stage [1]. This paper review the results of the commissioning concerning the transversal beam behavior, in particular the orbit correction system, results from the beam based alignment (BBA), and coupling. The orbit con- trol system of ALBA consists of 88 horizontal and vertical correctors, mounted as extra coils in the sextupole mag- nets, up to 104 LIBERA BPMs (brilliance version). The correctors magnets would be used for both static orbit cor- rection and for the fast orbit feedback mode, providing up to 1 mrad of correction in the static case. In phase one of the commissioning, the orbit has been corrected down to values of 50 μm rms, with an estimated emittance ratio in the order of 1% . INTRODUCTION The commissioning of the storage ring of the ALBA syn- chrotron started in February 2011, with the first stage (ma- chine without any narrow gap insertion devices) finishing in June 2011. The lattice description can be found in [2]. The orbit correction system consists of 88 horizontal and vertical correctors, located as extra coils in the sextupoles magnets, and 104 BPMs, equipped with Libera Brilliance electronics. The 88 corrector magnets will used for the slow orbit correction as well as for the fast orbit feedback system. During this stage of the commissioning all avalaible BPMs (in general 102 out of the 104) were used for cor- recting the orbit, with the target orbit being defined by the center of the quadrupoles. The RF frequency has not been included routinely in the correction, only adjusting it once in order to find the center frequency. Algorithm and Software The starting algorithm used for correcting the orbit is the well know inversion of the response matrix by means of the Singular Value Decomposition (SVD). The response ma- trix used have been the measured one, only using the theo- retical one at the start. After inclusion of the Beam Based Alignment constants, it was possible to correct the orbit us- ing up to 86 out of the 88 SVD eigenvalue in each plane. The software used is the setorbitgui routine of the Mat- lab MiddleLayer (MMA). The option to use Tikhonov reg- ularization in place of the simpler truncated SVD technique for inverting the response matrix has been added to the GUI. When using this method, the orbit can be corrected ∗ [email protected] using maximum corrector values a 30 % smaller thant when using the truncated SVD. BEAM BASED ALIGNMENT The BBA constant of the BPMs respect the center of the nearest quadrupoles have been measured two times, with the second measure performed after taking in accoung the results for the first round. Figure 1 show the total BBA constant measured. The results are reproducible to values under 10 μm, consistent with the noise in the BPMs at this stage of the commissioning. Most offsets are of the order of the 100 μm, but some peaks up to the 1 mm are present. The possible source of this large deviations have not been identified. 0 50 100 150 200 250 -1.5 -1 -0.5 0 0.5 1 1.5 s [m] [mm] Horizontal Vertical Figure 1: Offset from the electrical center of the BPMs to the magnetic center of the nearest quadrupoles (BBA off- sets). ORBIT EVOLUTION DURING COMMISSIONING BPM Noise In this stage of the commissioning, the switching mode of the BPM electronics was not activated, increasing the noise in the measurement of the orbit. Figure 2 shows the measured noise in the BPMs. The figure shows the change in the reading of the BPMs during a period of 180 seconds, with a new measure each second, respect the average value. Bare Orbit In the initial stage of the commissioning one corrector in each plane was needed for injection and accumulation ORBIT STUDIES DURING ALBA COMMISSIONING THPC056 Proceedings of IPAC2011, San Sebastián, Spain 3020 Copyright c ○ 2011 by IPAC’11/EPS-AG — cc Creative Commons Attribution 3.0 (CC BY 3.0) 02 Synchrotron Light Sources and FELs A05 Synchrotron Radiation Facilities
Transcript of Orbit Studies during ALBA Commissioning · 0 1 2 3 Horizontal [mm] mean rms max 0 1 2 3 Vertical 13...
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M. Muñoz∗, Z. Martı́, D. Einfeld, G. Benedetti, CELLS-ALBA, Bellaterra, Spain
Abstract
The 3rd generation light source ALBA is in the com-missioning stage [1]. This paper review the results of thecommissioning concerning the transversal beam behavior,in particular the orbit correction system, results from thebeam based alignment (BBA), and coupling. The orbit con-trol system of ALBA consists of 88 horizontal and verticalcorrectors, mounted as extra coils in the sextupole mag-nets, up to 104 LIBERA BPMs (brilliance version). Thecorrectors magnets would be used for both static orbit cor-rection and for the fast orbit feedback mode, providing upto 1 mrad of correction in the static case. In phase one ofthe commissioning, the orbit has been corrected down tovalues of 50 µm rms, with an estimated emittance ratio inthe order of 1% .
INTRODUCTION
The commissioning of the storage ring of the ALBA syn-chrotron started in February 2011, with the first stage (ma-chine without any narrow gap insertion devices) finishingin June 2011. The lattice description can be found in [2].The orbit correction system consists of 88 horizontal andvertical correctors, located as extra coils in the sextupolesmagnets, and 104 BPMs, equipped with Libera Brillianceelectronics. The 88 corrector magnets will used for theslow orbit correction as well as for the fast orbit feedbacksystem.
During this stage of the commissioning all avalaibleBPMs (in general 102 out of the 104) were used for cor-recting the orbit, with the target orbit being defined by thecenter of the quadrupoles. The RF frequency has not beenincluded routinely in the correction, only adjusting it oncein order to find the center frequency.
Algorithm and Software
The starting algorithm used for correcting the orbit is thewell know inversion of the response matrix by means of theSingular Value Decomposition (SVD). The response ma-trix used have been the measured one, only using the theo-retical one at the start. After inclusion of the Beam BasedAlignment constants, it was possible to correct the orbit us-ing up to 86 out of the 88 SVD eigenvalue in each plane.The software used is the setorbitgui routine of the Mat-lab MiddleLayer (MMA). The option to use Tikhonov reg-ularization in place of the simpler truncated SVD techniquefor inverting the response matrix has been added to theGUI. When using this method, the orbit can be corrected
using maximum corrector values a 30% smaller thant whenusing the truncated SVD.
BEAM BASED ALIGNMENT
The BBA constant of the BPMs respect the center of thenearest quadrupoles have been measured two times, withthe second measure performed after taking in accoung theresults for the first round. Figure 1 show the total BBAconstant measured. The results are reproducible to valuesunder 10 µm, consistent with the noise in the BPMs at thisstage of the commissioning. Most offsets are of the orderof the 100 µm, but some peaks up to the 1 mm are present.The possible source of this large deviations have not beenidentified.
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Figure 1: Offset from the electrical center of the BPMs tothe magnetic center of the nearest quadrupoles (BBA off-sets).
ORBIT EVOLUTION DURINGCOMMISSIONING
BPM Noise
In this stage of the commissioning, the switching modeof the BPM electronics was not activated, increasing thenoise in the measurement of the orbit. Figure 2 shows themeasured noise in the BPMs. The figure shows the changein the reading of the BPMs during a period of 180 seconds,with a new measure each second, respect the average value.
Bare Orbit
In the initial stage of the commissioning one correctorin each plane was needed for injection and accumulation
ORBIT STUDIES DURING ALBA COMMISSIONING
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Figure 2: Signal in the 102 working BPMs, measured dur-ing 180 s, at 2 Hz. Some BPMs present a large drift ofseveral 10s µm, but the noise is under the µm level.
but after reaching the right working point, and the injectionparameters have been optimized, it was possible to injectand store the beam without any correctors. The bare orbitis small ( 3), a sign of a good alignment.
Figure 3: Measurement of the bare orbit.
Best Correction
Starting from the bare orbit, using a measured responsematrix, and using the Tikhonov regularization method toinvert it, the orbit has been corrected down to values circa30 µm at all the BPMs, using a only 30 % of the avalaiblecorrector strength. Figures 4 and 5 show the results.
Figure 4: Optimal orbit correction. Orbit corrected at the102 BPMs, using the Tikhonov regularization.
Figure 5: Optimal orbit correction. Current in the correc-tors. The correctors can reach up to 10 A, corresponding to1 mrad of deflection.
Reproducibility
The orbit of the machine was very reproducible, withchanges up to 100 µm between days or when changing theconditions of the machine (cycling of the magnets, changesof the chromaticity). Figures 6 and 7 show the change in theorbit and correctors along the commissioning. The largereductions in orbit and corrector strength corresponds tothe setting of the right RF frequency (first large drop) andto the inclusion of the BBA offsets.
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Figure 6: Orbit evolution. Measured corrected orbit duringcommissioning. The first large reduction corresponds tothe fixing of the central frequency. The next one to theBBA offset inclusion in the correction.
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Figure 7: Orbit evolution: Corrector values correspondingto 6. Note that the mean value of the horizontal correctorsgoes to zero when the frequency is corrected.
COUPLING AND DISPERSION
The orbit correction system also compensate the cou-pling and the dispersion. Figure 8 shows a typical measure-ment of the horizontal and vertical dispersion after correct-ing the orbit. The vertical dispersion is under 10 mm. Themeasured coupling is between 0.5 % and 2 %. This value isconsistent with measurements of the beam size and of thelifetime.
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NEXT STEPS
Definition of the Golden Orbit
In the next steps of the commissioning, synchrotron lightwould be delivered routinely to the beam lines for commis-sioning. A golden orbit in 88 BPMs would be defined, andthe orbit will be corrected using only this BPMs, using theother 16 for monitoring. In the future, the 104 BPMs couldbe used for correction, including weights.
Feedback System
The Slow Orbit feedback has been already been tested,running as a Matlab application. The maximum rate of thepresent implementation is 0.5 Hz, and has proved capableof compensating the perturbation created by closing the gapof the multipole wiggler. The design of the Fast Orbit feed-back is finished, with the implementation under way, and isexpected to be commissioned before the end of 2012.
REFERENCES
[1] D. Einfeld, “Commissioning of ALBA” IPAC’11,September 2011, MOXAA01, This proceedings,http://www.jacow.org.
[2] M. Muñoz and D. Einfeld, “Lattice and beam dynamics of theALBA storage ring”,ICFA Beam Dyn. Newslett. 44, 2007.
THPC056 Proceedings of IPAC2011, San Sebastián, Spain
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02 Synchrotron Light Sources and FELs
A05 Synchrotron Radiation Facilities
