On Injection Beam Loss at the SPring-8 Storage Ring

1. On Injection Beam Lossatthe SPring-8 Storage Ring Masaru TAKAO & J. Schimizu, K. Soutome, and H. Tanaka JASRI / SPring-8 Non-linear Beam Dynamics WS

2. Outline • Motivation • SPring-8 storage ring • Injection efficiency measurement • Tracking simulation • Improvement of injection efficiency • Beam collimation in transport line • Low chromaticity operation • Beta-distortion correction • Summary Non-linear Beam Dynamics WS

3. Motivation • Injection beam loss is a very important issue for top-up operation. • Demagnetization of insertion devices (ID) • Radiation safety • Before introducing top-up operation, we intensively studied injection beam loss at the Spring-8 storage ring. • Effects of ID gap, chromaticity, beta-distortion, … Non-linear Beam Dynamics WS

4. SPring-8 Storage Ring Parameters @ 2002.9 ~ 2003.7 Non-linear Beam Dynamics WS

5. Storage Ring Optics • Modified Chasman-Green optics • 4 magnet-free straight sections of 30 m long • 36 normal cells, 4 long straight sections Non-linear Beam Dynamics WS

6. Insertion Devices @ SPring-8 in-vacuum ID • 27 ID's • in-vacuum: 21, out-vacuum: 6. • One of in-vacuum undulators (ID19) is 25 m long. standard ID long ID Non-linear Beam Dynamics WS

7. Insertion Device Parameters cf. vacuum chamber height: 40 mm Non-linear Beam Dynamics WS

8. Injection Efficiency Measurement • Turn-by-turn current monitor • ICT + oscilloscope. • Used for study. • Voltage sum of 4 electrodes of turn-by-turn BPM • Influenced by synchrotron motion. • (DCCT @ storage ring) - (BCM @ beam transport) • Monitoring in user operation. Non-linear Beam Dynamics WS

9. Experiments • Injection efficiency is measured for various ID gap. • Use ID as a scraper. • Measured for ID19 (long), ID20, ID37 (standard). standard undulator long undulator Non-linear Beam Dynamics WS

10. Dependence of injection efficiency on ID gap • Gap where injection efficiency starts to decrease is different between long undulator and standard ones. • The injection efficiencies corresponding to the same effective gaps of ID's coincide. • The effective gap of injection efficiency starting to drop corresponds to the minimum effective height of the vacuum chamber. • Injection efficiency is limited by transverse dynamics. Non-linear Beam Dynamics WS

11. Tracking Simulation • "Racetrack" based tracking code. • 6 x 6 formalism. • Symplectic integration. • Using ring model (error fields) derived by response matrix analysis. • With physical apertures. • 1000 particles, 1000 revolutions. Non-linear Beam Dynamics WS

12. Injection Beam Parameters cf. booster synchrotron lattice: FODO. circumference: 400 m. Non-linear Beam Dynamics WS

13. Simulation Results • Decay rate of simulation is somewhat faster than that of experiment. • Dependence of injection efficiency on ID gap is enough described by simulation. experiment simulation Non-linear Beam Dynamics WS

14. Lost Points of Injection Beam • Loss points detected by simulation. Non-linear Beam Dynamics WS

15. Lost Particle Distribution in Initial Phase Space • Lost particle distribution in phase space of injection beam detected by simulation. • Horizontal phase space: lost particles localize in large amplitude side. • Vertical & longitudinal phase spaces: lost particles uniformly distributed. Non-linear Beam Dynamics WS

16. Beam Collimation in Transport Line • Beam collimator in horizontal direction was installed in transport line from booster to storage ring to eliminate unnecessary beam tail.  = 0. 544mm  = 1. 249mm booster SR Non-linear Beam Dynamics WS

17. Influence of Chromaticity 1 • Lowering the chromaticity improves injection efficiency. • In low chromaticity condition, ID gap dependence of the injection efficiency is scarcely observed. high chromaticity ( 8, 8 ) low chromaticity ( 2, 2 ) Non-linear Beam Dynamics WS

18. Influence of Chromaticity 2 • Particle distribution in vertical direction • long undulator entrance. • after 500 revolutions. • without aperture limit. Non-linear Beam Dynamics WS

19. Beta-Distortion Correction • Beta-distortion was corrected by using 48 auxiliary quadrupole magnet power supplies. • Beta-distortion was measured by response matrix analysis. • Correction performance was checked by re-measurement of beta-distortion after correction. • It is observed beta-distortion correction improved injection efficiency by about 15 %. Non-linear Beam Dynamics WS

20. Beta-Distortion Correction before (rms distortion: 7.4%) * Half of the Ring is shown. after (rms distortion: 1.9%) Non-linear Beam Dynamics WS

21. Beta-Distortion Correction before (rms distortion: 7.3%) after (rms distortion: 1.5%) Non-linear Beam Dynamics WS

22. Influence of Beta-Distortion • Particle distribution in vertical direction • beta-distortion correction ON/OFF. • at long undulator entrance. • without aperture limit. Non-linear Beam Dynamics WS

23. Summary • Injection efficiency at the SPring-8 storage ring was investigated by experiments and simulations. • Simulation well describes the experiments. • Injection efficiency is mainly limited by vertical aperture. • Following the implication by the simulation, we improved the injection efficiency. • Injection beam collimator. • Lowering chromaticity. • Correction of beta-distortion. Non-linear Beam Dynamics WS