1. 1 Alternative ILC Bunch Compressor 7 th Nov. 2007 KNU (Kyungpook National Univ.) Eun-San Kim

2. 2 Introduction  Alternative BC has two rf sections and two chicanes with 4 bending magnets each. Each chicane includes a 34 m lattice of bending.  Bunch lengths of 6 mm rms and 9 mm rms can be compressed to 0.15 mm rms and 0.3 mm rms in the BC, respectively.  We performed the lattice tunings to control the emittance growths with conservative machine errors. : It was shown that the system was error tolerant.  It was highly recommended by EDR phase to perform the alternative BC since it would permit a significant cost savings without sacrificing performance.

3. 3 Designed lattice locations of 4 skew quadrupoles

4. 4 Emittance Tuning  Correction of vertical dispersion that is generated by skew components was performed by using of 4 skew-quadrupoles in rf linac section.  We performed both dispersion correction and orbit correction at the same time such that they have a minimum value.

5. 5 Lattice distortion due to Q vertical alignment error (300  m rms) Without lattice correction With lattice correction

6. 6 Emittance vs. Q-Vertical alignment error

7. 7 Lattice distortion due to bending rotation error (300  rad rms) Without lattice correction With lattice correction

8. 8 Emittance growth vs. Bending rotation error

9. 9 Lattice distortion due to Q-Horizontal alignment error (300  m rms) Without lattice correctionWith lattice correction

10. 10 Emittance growth vs. Q-Horizontal alignment error

11. 11 Lattice distortion due to Quadrupole rotation error (300  rad rms ) Without lattice correctionWith lattice correction

12. 12 Emittance growth vs. Q Rotation error

13. 13 Lattice distortion due to Bending vertical misalignment error (300  m rms ) Without lattice correctionWith lattice correction

14. 14 Emittance growth vs. Bending misalignment error

15. 15 Considered 6 machine errors Error Magnitude H-misalignment in Q 300  m rms V-misalignment in Q 300  m rms Rotation in Q 300  rad rms V-misalignment in B 300  m rms H-misalignment in B 300  m rms Rotation in B 300  rad rms

16. 16 Lattice distortion due to 6 machine errors Growths of emittance : factors of 1 / 1.04 in H / V Without lattice correction Growths of emittance : factors of 1.48 / 254 in H / V With lattice correction

17. 17 80 and 70 % of seed number shows emittance growth less than 10 % in x and y-direction. Effect of random seed number With 6 machine errors

18. 18 Effect of BPM offset error Offset error of 300  m rms shows negligible emittance growth. With 6 machine errors

19. 19 Longitudinal phase space Initial bunch length of 6 mmInitial bunch length of 9 mm Initial After chicane 1 After chicane 2

20. 20 Main parameters in BC ( ) denotes parameters for initial bunch length of 9 mm rms.

21. 21 Effects of ISR and CSR on emittances At Chicane 1At Chicane 2  x for 6 mm bunch length  x for 9 mm bunch length CSR 8.28  m 8.22  m ISR 8.37  m 8.92  m CSR+ISR CSR 8.42  m 8.38  m CSRCSR+ISR 8.47  m 8.90  m CSR+ISR 8.65  m 9.14  m ISR is a main source to emittance growth.

22. 22 Fluctuation in bunch length 100 successive bunches due to rf voltage jitter (left) and rf phase angle jitter (right).

23. 23 ILC bunch compressors ( Nov. 2005 ) Alternative BC Baseline BC Bunch length (mm) 0.15 Energy spread (%) 2.6 2.46 Horizontal emittance (  m) 8.3 (ISR) 8.2 (ISR) Vertical emittance (  m) 0.02 Beam energy (GeV) 13  Performance of the alternative BC showed good agreements with results of cross checks by SLAC groups and showed comparable values with baseline BC. * Initial bunch length : 6 mm

24. 24 Emittance growth in ILC BCs ( Nov. 2005 ) By SLAC group * Initial bunch length : 6 mm Errors Alternative BCBaseline BC 10  m BPM resolution 5.85 nm 5.34 nm 500  m cavity alignment 2.83 nm 3.04 nm 75  rad cavity rotation 3.14 nm 2.68 nm

25. 25 Summary  Studies on performance, error tolerance and jitter of alternative BC are presented.  Results on emittance tuning in the alternative BC show that the system is error tolerant.  The work-packages of EDR include the alternative BC and more improvements will be performed in the coming EDR phase.