1

Alternative ILC Bunch Compressor

7th Nov. 2007

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 t

he alternative BC since it would permit a significant cost savings without sacrificing performance.

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Designed lattice

locations of 4 skew quadrupoles

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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.

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Lattice distortion due to Q vertical alignment error (300m rms)

Without lattice correction With lattice correction

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0 200 400 600 800 1000

1

10

100

1000yom

y/ yo

RMS quadrupole vertical alignment error (m)

without correction with correction

Emittance vs. Q-Vertical alignment error

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Lattice distortion due to bending rotation error (300 rad rms)

Without lattice correction With lattice correction

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0 200 400 600 800 1000

1

10

100

yom

without correction with correction

RMS Bending rotation error (m)

y/ yo

Emittance growth vs. Bending rotation error

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Lattice distortion due to Q-Horizontal alignment error (300 m rms)

Without lattice correction With lattice correction

10

0 200 400 600 800 1000

1

10

RMS quadrupole horizontal alignment error (m)

x/ xo

xom without correction with correction

Emittance growth vs. Q-Horizontal alignment error

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Lattice distortion due to Quadrupole rotation error (300 rad rms )

Without lattice correction With lattice correction

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0 200 400 600 800 1000

1

10

yom

RMS quadrupole rotation error (m)

y/ yo

without correction with correction

Emittance growth vs. Q Rotation error

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Lattice distortion due to Bending vertical misalignment error (300 m rms )

Without lattice correction With lattice correction

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0 200 400 600 800 1000

1

10

yom

y/ yo

RMS Bending vertical alignment error (m)

without correction with correction

Emittance growth vs. Bending misalignment error

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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

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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

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0 50 100 150 2000.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

y/ yo

Number of Random Seed

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

0 50 100 150 2000.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

x/ xo

Number of Random Seed

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Effect of BPM offset error

Offset error of 300 m rms shows negligible emittance growth.

165 170 175 180 185 190 195 200

1.0

1.1

1.2

1.3

1.4

1.5

x/ xo

Number of Random Seed

without BPM offset with 300 m BPM offset

With 6 machine errors

165 170 175 180 185 190 195 2000.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4 without BPM offset with 300 m BPM offset

Y/ Yo

Number of Random Seed

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Longitudinal phase space

Initial bunch length of 6 mm Initial bunch length of 9 mm

Initial

After chicane 1

After chicane 2

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Main parameters in BC

( ) denotes parameters for initial bunch length of 9 mm rms.

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Effects of ISR and CSR on emittances

At Chicane 1 At Chicane 2 x for 6 mm bunch length

x for 9 mm bunch length

CSR CSR 8.28 m 8.22 m

ISR ISR 8.37 m 8.92 m

CSR+ISR CSR 8.42 m 8.38 m

CSR CSR+ISR 8.47 m 8.90 m

CSR+ISR CSR+ISR 8.65 m 9.14 m

ISR is a main source to emittance growth.

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Fluctuation in bunch length

0 20 40 60 80 1000.94

0.96

0.98

1.00

1.02

1.04

1.06

Number of bunches

Re

latv

e b

un

ch

le

ng

th

1% rms voltage error 2% rms voltage error

0 20 40 60 80 1000.94

0.96

0.98

1.00

1.02

1.04

1.06

0.1 degree rms phase error 0.3 degree rms phase error

Number of bunchesR

ela

tve

bu

nc

h l

en

gth

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

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ILC bunch compressors ( Nov. 2005 )

Alternative BC Baseline BC

Bunch length (mm) 0.15 0.15

Energy spread (%) 2.6 2.46

Horizontal emittance (m) 8.3 (ISR) 8.2 (ISR)

Vertical emittance (m) 0.02 0.02

Beam energy (GeV) 13 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

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Emittance growth in ILC BCs ( Nov. 2005 )

By SLAC group * Initial bunch length : 6 mm

Errors Alternative BC Baseline 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

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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.