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

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 Designed lattice locations of 4 skew quadrupoles

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

6 Emittance vs. Q-Vertical alignment error

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

8 Emittance growth vs. Bending rotation error

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

10 Emittance growth vs. Q-Horizontal alignment error

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

12 Emittance growth vs. Q Rotation error

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

14 Emittance growth vs. Bending misalignment error

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

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

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

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

23 ILC bunch compressors ( Nov ) Alternative BC Baseline BC Bunch length (mm) 0.15 Energy spread (%) 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 Emittance growth in ILC BCs ( Nov ) 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 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.