28-May-2008 Non-linear Beam Dynamics WS 1

On Injection Beam Loss

at

the SPring-8 Storage Ring

Masaru TAKAO

&

J. Schimizu, K. Soutome, and H. Tanaka

JASRI / SPring-8

28-May-2008 Non-linear Beam Dynamics WS 2

Outline

• Motivation

• SPring-8 storage ring

• Injection efficiency measurement

• Tracking simulation

• Improvement of injection efficiency– Beam collimation in transport line

– Low chromaticity operation

– Beta-distortion correction

• Summary

28-May-2008 Non-linear Beam Dynamics WS 3

Motivation

• Injection beam loss is a very important issue

for top-up operation.

– Demagnetization of insertion devices (ID)

– Radiation safety

• Before introducing top-up operation, we

intensively studied injection beam loss at the

Spring-8 storage ring.

– Effects of ID gap, chromaticity, beta-distortion, …

28-May-2008 Non-linear Beam Dynamics WS 4

SPring-8 Storage Ring Parameters

energy 8 GeV

circumference 1.5 km

horizontal / vertical betatron tune 40.15 / 18.35

horizontal / vertical chromaticity 8.0 / 8.3

natural emittance 3.4 nmrad

emittance coupling ratio 0.002

synchrotron tune 0.01

energy spread 0.0011

bunch length (zero current limit) 12.5 ps

@ 2002.9 ~ 2003.7

28-May-2008 Non-linear Beam Dynamics WS 5

Storage Ring Optics

• Modified Chasman-Green optics• 4 magnet-free straight sections of 30 m long• 36 normal cells, 4 long straight sections

-10

0

10

20

30

40

50

60

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150

Bet

atro

n F

un

ctio

n [

m]

Disp

ersion F

un

ction [m

]

Long Straight SectionNormalCG Cell

Path Length [m]

NormalCG Cell

xy

x

28-May-2008 Non-linear Beam Dynamics WS 6

Insertion Devices @ SPring-8

• 27 ID's– in-vacuum: 21, out-vacuum: 6.– One of in-vacuum undulators (ID19) is 2

5 m long.

standard ID long ID

in-vacuum ID

28-May-2008 Non-linear Beam Dynamics WS 7

Insertion Device Parameters

ID19 (long) ID20 (standard)

length 25 m 4.5 m

minimum gap 12 mm 7 mm

maximum gap 50 mm 50 mm

vertical beta @ center 14.1 m 5.6 m

vertical beta @ ends 25.2 m 6.5 m

cf. vacuum chamber height: 40 mm

28-May-2008 Non-linear Beam Dynamics WS 8

Injection Efficiency Measurement• Turn-by-turn current monitor

– ICT + oscilloscope.

– Used for study.

• Voltage sum of 4 electrodes of turn-by-turn BPM

– Influenced by synchrotron motion.

• (DCCT @ storage ring) - (BCM @ beam transport)

– Monitoring in user operation.

0.8

0.9

1

0 500 1000 1500 2000

current monitorBPM voltage sum

Inje

ctio

n E

ffic

ienc

y

Turn

28-May-2008 Non-linear Beam Dynamics WS 9

Experiments• Injection efficiency is measured for various ID gap.

– Use ID as a scraper.• Measured for ID19 (long), ID20, ID37 (standard).

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

ID19

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm

13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mm

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

ID20

Inje

ctio

n E

ffic

ienc

y

Turn

7 mm8 mm9 mm10 mm

50 mm ~ 11 mm

long undulator standard undulator

28-May-2008 Non-linear Beam Dynamics WS 10

Dependence of injection efficiency on ID gap• Gap where injection efficiency starts to decrease is different between l

ong undulator and standard ones.• The injection efficiencies corresponding to the same effective gaps of

ID's coincide.• The effective gap of injection efficiency starting to drop corresponds to

the minimum effective height of the vacuum chamber.• Injection efficiency is limited by transverse dynamics.

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50

ID19ID20ID37

Inje

ctio

n E

ffic

ien

cy

Gap [mm]

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20

ID19ID20ID37

Inje

ctio

n E

ffic

ien

cy

Effective Gap (Gap/y1/2) [mm/mm1/2]

Minimum effectivechamper height

28-May-2008 Non-linear Beam Dynamics WS 11

Tracking Simulation

• "Racetrack" based tracking code.

• 6 x 6 formalism.

• Symplectic integration.

• Using ring model (error fields) derived by response ma

trix analysis.

• With physical apertures.

• 1000 particles, 1000 revolutions.

28-May-2008 Non-linear Beam Dynamics WS 12

Injection Beam Parameters

horizontal emittance 220 nmrad

emittance coupling 0.002

energy spread 0.0013

bunch length 63 ps

off-set from stored beam orbit 10 mm

cf. booster synchrotron lattice: FODO. circumference: 400 m.

28-May-2008 Non-linear Beam Dynamics WS 13

Simulation Results• Decay rate of simulation is somewhat faster than that of

experiment.• Dependence of injection efficiency on ID gap is enough

described by simulation.

0.6

0.7

0.8

0.9

1

0 200 400 600 800 1000 1200

ID19

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mm

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

ID19

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm

13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mm

experiment simulation

28-May-2008 Non-linear Beam Dynamics WS 14

Lost Points of Injection Beam• Loss points detected by simulation.

50

100

150

0 500 1000 1500

ID19 gap = 50 mm (full open)ID19 gap = 12 mm (minimum)

Nu

mb

er o

f L

ost

Par

ticl

es

Path Length fron Injection Point [m]

0

Long straight sections

Long undulatorSeptum wall

(injection section)

ID 19 gap condition main loss points

minimum (12 mm) ends of undulator

maximum (50 mm)quadrupole magnets in matching section (highest vertical beta at upstream and down stream of long straight sections)

-10

0

10

20

30

40

50

60

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 50 100 150

Bet

atro

n F

unc

tion

[m

]

Disp

ersion F

un

ction [m

]

Long Straight SectionNormalCG Cell

Path Length [m]

NormalCG Cell

xy

x

28-May-2008 Non-linear Beam Dynamics WS 15

Lost Particle Distribution in Initial Phase Space• Lost particle distribution in phase space of injection beam

detected by simulation.• Horizontal phase space: lost particles localize in large amplitude

side.• Vertical & longitudinal phase spaces: lost particles uniformly

distributed.

-0.015

-0.0075

0

0.0075

0.015

-0.2 -0.1 0 0.1 0.2

capturedlost

y' [

mra

d]

y (mm)

-0.005

-0.0025

0

0.0025

0.005

-80 -40 0 40 80

capturedlost

p /

ps (mm)

-0.6

-0.4

-0.2

0

0.2

0.4

-16 -14 -12 -10 -8 -6

capturedlost

x' [

mra

d]

x (mm)

28-May-2008 Non-linear Beam Dynamics WS 16

Beam Collimation in Transport Line• Beam collimator in horizontal direction was installed in transport

line from booster to storage ring to eliminate unnecessary beam tail.

= 0. 544mm = 1. 249mm

50

60

70

80

90

100

0 1 2 3 4 5 6

All ID Gap Full OpenAll ID Gap Full Close

Inje

ctio

n E

ffic

ien

cy [

%]

Collimator Gap (Half Width) []

booster

SR

28-May-2008 Non-linear Beam Dynamics WS 17

Influence of Chromaticity 1• Lowering the chromaticity improves injection efficiency.• In low chromaticity condition, ID gap dependence of the injection

efficiency is scarcely observed.

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

ID19

Inje

ctio

n E

ffic

ienc

y

Turn

50 mm ~ 12 mm

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

ID19

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm

13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mm

high chromaticity ( 8, 8 ) low chromaticity ( 2, 2 )

28-May-2008 Non-linear Beam Dynamics WS 18

Influence of Chromaticity 2

• Particle distribution in vertical direction– long undulator entrance.– after 500 revolutions.– without aperture limit.

10-1

100

101

102

103

104

105

-15 -10 -5 0 5 10 15

( x, y ) = ( 8, 8 )

( x, y ) = ( 2, 2 )

Nu

mb

er o

f P

arti

cles

y [mm]

0.6

0.7

0.8

0.9

1

0 200 400 600 800 1000 1200

( x, y ) = ( 8, 8 )

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mm

ID19 gap

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

( x, y ) = ( 2, 2)

Inje

ctio

n E

ffic

ienc

y

Turn

50 mm ~ 12 mmID19 gap

28-May-2008 Non-linear Beam Dynamics WS 19

Beta-Distortion Correction

• Beta-distortion was corrected by using 48 auxiliary qua

drupole magnet power supplies.

• Beta-distortion was measured by response matrix anal

ysis.

• Correction performance was checked by re-measurem

ent of beta-distortion after correction.

• It is observed beta-distortion correction improved inject

ion efficiency by about 15 %.

28-May-2008 Non-linear Beam Dynamics WS 20

Beta-Distortion Correction

before (rms distortion: 7.4%)

after (rms distortion: 1.9%)

0

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40

0 100 200 300 400 500 600 700

x[m]

s [m]

0

10

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30

40

0 100 200 300 400 500 600 700

x[m]

s [m]

* Half of the Ring is shown.

28-May-2008 Non-linear Beam Dynamics WS 21

Beta-Distortion Correction

before (rms distortion: 7.3%)

after (rms distortion: 1.5%)

0

20

40

60

0 100 200 300 400 500 600 700

y[m]

s [m]

0

20

40

60

0 100 200 300 400 500 600 700

y[m]

s [m]

28-May-2008 Non-linear Beam Dynamics WS 22

Influence of Beta-Distortion• Particle distribution in vertical direction

– beta-distortion correction ON/OFF.

– at long undulator entrance.

– without aperture limit.

0.4

0.6

0.8

1

0 200 400 600 800 1000 1200

with correction

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mm

ID19 gap

0.4

0.6

0.8

1

0 500 1000 1500 2000

without correction

Inje

ctio

n E

ffic

ienc

y

Turn

12 mm13 mm14 mm15 mm16 mm18 mm20 mm

50 mm ~ 22 mmID19 gap

10-1

100

101

102

103

104

105

-20 -10 0 10 20

w/o correctionwith correction

Nu

mb

er o

f P

arti

cles

y [mm]

28-May-2008 Non-linear Beam Dynamics WS 23

Summary

• Injection efficiency at the SPring-8 storage ring was

investigated by experiments and simulations.

• Simulation well describes the experiments.

• Injection efficiency is mainly limited by vertical aperture.

• Following the implication by the simulation, we

improved the injection efficiency.– Injection beam collimator.

– Lowering chromaticity.

– Correction of beta-distortion.