BL 5 EPU coupling Strong skew gradient varies

BL 5 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).

BL 5 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

EPU coupling correction schemes

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

PM skew quad end correctors a 3 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 BL 12 undulator). At 50 mm gap, skew gradient = 375 Gauss, skew octupole = -11. 8 G/cm 2

EPU skew quad end correctors

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

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 m. A in 31 consecutive bunches 210 mm 45 mm 30 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 mm, *2 layers (above and below the beampipe) increase gap 0. 3 mm. • 576 Gauss integrated correction • Design in progress.

Fit skew gradients from 2004 -10 -08 LOCO measurements

EPU coupling • Jeff Corbett, 7/14/04: With the EPU out, closest tune approach is ~400 Hz. If we set skew quads to zero closed tune approach is ~2 k. Hz. With the EPU at 30 mm closest tune approach is ~10 k. Hz. • 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 BL 4&7 skew gradient spec. • Row phases for this measurement were for vertical polarization (horizontal field)