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Alternative Bunch Compressor

30th Sep. 2008

KNU Eun-San Kim

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Introduction

Alternative BC has two rf sections and two chicanes with 4 bending magnets each. Length of each bending was reduced from 6.8 m to 2.4.

Bunch lengths of 6 mm rms and 9 mm rms can be compressed to 0.15 mm rms and 0.3 mm rms, respecti

vely.

We performed the lattice tunings to control the emittance growths with machine errors. : It was shown that the system was error tolerant.

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Designed lattice

locations of 4 skew quadrupoles

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Main parameters

• Initial bunch length 6 mm 9 mm

• Final bunch length 0.15 mm 0.3 mm

• Final emittance (H/V) 8.6/0.02 8.8/0.02(9.1/0.2)

• R56 in chicane 1 474.2 mm

• R56 in chicane 2 50.8 mm

• Initial beam energy 5 GeV 5 GeV

• Final beam energy 13.2 GeV 14.5 GeV

• Final energy spread(%) 2.4(2.6) 2.1(2.4)

( ) : 6.8 m bending magnet

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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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Emittance Tuning

Correction of vertical dispersion that is generated by skew components was performed by using of 4 skew-quadrupoles.

We performed both dispersion correction and orbit correction at the same time such that they have a minimum value.

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Considered 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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Vertical alignment error in Q*

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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Rotation error in Bending

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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Horizontal alignment error in Q*

Without lattice correction With lattice correction

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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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Rotation error in Q*

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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Bending vertical misalignment error

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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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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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 8.20 m 8.14 m

ISR ISR 8.43 m 8.66 m

CSR+ISR CSR 8.35 m 8.33 m

CSR CSR+ISR 8.45 m 8.62 m

CSR+ISR CSR+ISR 8.63 m 8.8 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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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.