1. Optics for Skew Correction and Emittance Measurement Leo Jenner This talk is going to look familiar if you were at the recent LC-ABD meeting in Manchester…

2. 2 4D symmetric beam matrix =  Coupling terms To minimise the vertical emittance, especially for a flat beam, it is desirable to remove any cross-plane (x-y) correlations/couplings

3. 3 Sources of Skew Linac is main source of skew in ILC Skew correction section comes immediately afterwards and is the first sub-system of BDS

4. 4 Ideal Skew Correction + Emittance Measurement Layout 4 orthogonal skew quadrupoles correct xy, x’y’, x’y, xy’ 4 wire scanners / laser wires for emittance measurement

5. 5 4D measurement simulation – 6 wire scanners required Measured Emittance Input Emittance Perturbed Projected Emittance Unperturbed Projected Emittance High Rejection Factor with realistic measurement errors

6. 6 2D Measurement simulation with 4 wires scanners Only 4 scanners – shorter, cheaper Scan in x and y separately Coupling is inferred from difference between measured and expected emittance – it seems this is good enough! Calculated projected emittance Unperturbed projected emittance

7. 7 Correction procedure Perturb beam with skew quads Perturb beam with skew quads Measure beam parameters with scanners Measure beam parameters with scanners Infer coupling Infer coupling Calculate skew correction Calculate skew correction Apply to skew quadrupoles Apply to skew quadrupoles (Iterate) (Iterate)

8. 8 Skew Quad Scanning Scan quad strength around nominal value to find minimum Fit parabola Extract parameters

9. 9 Coupling Correction in Action Skew Quad Scan Number Projected/Actual emittance

10. 10 Application1: ATF2

11. 11 Application 2: ILC BDS Skew Section

12. 12 Summary and Future Plans Use ‘real’ ILC errors Use ‘real’ ILC errors Investigate alternative 4D methods Investigate alternative 4D methods Investigate 2D/4D and/or BPM method Investigate 2D/4D and/or BPM method Incorporate simulation of Laserwire Incorporate simulation of Laserwire Tweaking of ATF2/ILC optics Tweaking of ATF2/ILC optics