BL5 EPU coupling Strong skew gradient varies with gap (not much variation with row phase) 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).

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

EPU coupling correction schemes

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

PM skew quad end correctors At 30 mm gap, skew corrector generates required correction plus -5.8 G/cm 2 skew octupole (compare to 40 G/cm 2 specification for BL12 undulator). At 50 mm gap, skew gradient = 375 Gauss, skew octupole = G/cm 2 {At 40 mm gap, skew gradient = 235 Gauss, skew octupole = -5.3 G/cm 2 } a3a3 a3a3

EPU skew quad end correctors

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

Lifetime reduction independent of row phase

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

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

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.)

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

Fit skew gradients from LOCO measurements

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)

A.P., June 28, 2004

A.P., June 29, 2004

A.P., July 13, 2004

A.P., July 14, 2004

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.