BL5 EPU coupling

1. BL5 EPU coupling • Strong skew gradient varies with gap (not much variation with row phase). 570 G @ 30 mm gap • Implemented permanent magnet correctors on each end of device (R. Carr). • Good correction at 30 mm gap • Overcorrection at larger gaps • Despite poor coupling correction, lifetime decreases by 15% at gaps ~45 mm. • Beam-based measurements indicate only weak nonlinear fields • Cause of lifetime reduction remains a mystery • Design of electromagnet skew quad corrector in progress (R. Carr).

2. BL5 EPU ops., June 24-25 • Strong coupling; varies with gap and a bit with row phase. EPU mode Lifetime varies with gap changes Lifetime varies with row phase change

3. EPU coupling correction schemes

4. EPU coupling correction schemes

5. Permanent magnet skew corrector Four bar magnets at each end of EPU EPU integrated skew gradient vs. gap - corrector - EPU error + + + + Over-corrects at intermediate gaps. - -

6. PM skew quad end correctors a3 a3 At 30 mm gap, skew corrector generates required correction plus -5.8 G/cm2 skew octupole (compare to 40 G/cm2 specification for BL12 undulator). At 50 mm gap, skew gradient = 375 Gauss, skew octupole = -11.8 G/cm2 {At 40 mm gap, skew gradient = 235 Gauss, skew octupole = -5.3 G/cm2}

7. EPU skew quad end correctors

8. Lifetime vs. EPU gap after PM skew corrector installed, lifetime reduction at intermediate gaps, despite larger coupling at these gaps!? 4.2 A*hr 3.6 A*hr

9. Lifetime reduction independent of row phase

10. LOCO analysis of coupling vs. gap with skew corrector installed: confirms coupling larger at 45 mm, despite lower lifetime:

11. Lifetime reduction at 45 mm gap with 100 mA in 31 consecutive bunches 210 mm 45 mm 30 mm

12. Dynamic aperture and beam-based nonlinear dynamics measurements indicate lifetime reduction for EPU at 45 mm not associated with nonlinear fields. (Analysis not yet fully completed.)

14. Electromagnet skew corrector • Kapton tape, total thickness 150 mm, *2 layers (above and below the beampipe) increase gap 0.3 mm. • 576 Gauss integrated correction • Design in progress.

18. Fit skew gradients from 2004-10-08 LOCO measurements

19. EPU coupling • Jeff Corbett, 7/14/04: With the EPU out, closest tune approach is ~400Hz. If we set skew quads to zero closed tune approach is ~2kHz. With the EPU at 30 mm closest tune approach is ~10kHz. • Analyzing response matrices from 6/29/04: • Integrated skew gradient from EPU at 30 mm is 570 Gauss. • 20% stronger than strongest skew corrector • 11 times stronger than BL4&7 skew gradient spec. • Row phases for this measurement were for vertical polarization (horizontal field)

20. A.P., June 28, 2004

21. A.P., June 29, 2004

22. A.P., July 13, 2004

23. A.P., July 14, 2004

24. EPU mode during 2004 run: • 23:00 16 June, 4 hours, A.P. • 06:00 24 June, 40 hours, ops. • 29 June, A.P. • 14 July, A.P.