JASRI Acc Div.�Linac GroupH. Hanaki

1 Overview of SPring-8 linac2 Beam stabilization • Stabilization of RF amplitude & phase • Synchronization of linac RF with ring RF • Energy compression system (ECS) • Feedback control3 Summary

Beam Stabilization in SPring-8 Linac

Beam energy instability of SPring-8 linac is 0.01% rms.

How have we achieved it •••

Injection beam Booster synchrotron NewSUBARU

Pulse widthPeak current

Beam energyRepetition rate

Energy spread

1 GeV1 pps1 ns2 A± 0.5 %

1 GeV1 pps40 ns70 mA± 0.3 %

1 GeV1 pps1 ns200 ± 0.2 %

Injection beam

Booster synchrotron NewSUBARU

Pulse widthPeak current

Beam energyRepetition rate

Energy spread

1 GeV1 pps1 ns2 A± 0.3 %

1 GeV1 pps40 ns70 mA± 0.5 %

1 GeV1 pps1 ns200 mA± 0.2 %

NewSUBARUNewSUBARU

1-GeV linac1-GeV linac

8-GeV booster synchrotron8-GeV booster synchrotron

8-GeV storage ring8-GeV storage ring

Thermionic electron gun

Bunching section

Accelerating structure

Linac synchrotronbeam transport line

80 MW klystron

Beam energy 1.2 GeV max.Beam current 2 ABeam pulse width 250 ps, 1 ns, 40 nsRF frequency 2856 MHzRepetition 60 ppsKlystron 80 MW x 13Acc. structure 3 m x 26Length of linac 140 m

Present Linac RF System

ECS

ChicaneGUN

OSC

PIN Mod.Amp

AttenuatorPhase Shifter

80MW Klystron (13 sets)

Prebuncher Buncher H0 Acc. H1 Acc. M18 Acc. M20 Acc.

Drive Line (90 m)

PLL-Stabilized Coaxial Line

2856MHzΦ Φ

Φ Φ Φ

Φ

Φ

Φ

Beam Injection Instability in 1998

0.5

-0.5

0.0

15 30 45 600Time (minutes)

Ene

rgy

Var

iatio

n (%

)

0

5

1 0

1 5

2 0

2 5

3 0

0 2 4 6 8 1 0

Bea

m c

urre

nt [m

A]

Time [hour]

WCM-M20@1 GeV straight line

9.0% (rms)WCM-LS@LSBT

1 Stabilization of RF amplitude & phase Investigate variation chains

Stabilization of their origins or devices 2 Reduce beam loading fluctuation

Synchronization of linac RF with ring RF3 Compensate accidental energy variation

Introduce Energy Compression System (ECS)4 Reduce residual beam position drift

Introduce feedback control

No SHB!

Strategy for stabilizing beam energy

Long Period Variation Chain

Cooling watertemperature

Line voltage

RF phase in longtransmission line

RF phase in acc. guide

Klystron RF phase

Klystron RF amplitude

Beam energy variation

Phase noise of RF system

Asynchronousityof beam pulse and linac RF

PFN voltage ofmodulator

Shot-by-Shot Variation Chain

Roomtemperature

RF phase in lowpower RF system

Klystron RF phase

RF beam loading

Variation chains in SPring-8 linac

Bunch chargedistribution

No SHB

Room temperature stabilization• Readjustment of air conditioners• Covering the long drive line with heat jackets• Circulating temperature stabilized water inside the jackets Klystron temperature stabilization• Improvement of water cooling system Isolate line voltage variation• Stabilization of Pulse Forming Network

(PFN) voltage by improving modulator regulation circuits

Reduction of long-period RF variation

10 deg. / 4˚C

< 1 deg. / 1˚C

90 m long main drive line

H0 klystron

90 m long main drive line

H0 klystron

Room temperature stabilization

Phase variation

10 deg.

4 ˚C

< 1 deg.

< 1 ˚C

2.4 deg. / 3˚C

< 0.5 deg. / 0.5˚C

-11

-10

-9

-8

-7

-6

-5

-4

-3

25

30

35

40

45

0 0.5 1 1.5 2

Ph

ase

[deg

]

Co

olin

g w

atertem

peratu

re [˚C]

Time [hours]

Cooling water temperature

Phase of 80 MW klystron

-11

-10

-9

-8

-7

-6

-5

-4

-3

25

30

35

40

45

0 0.5 1 1.5 2

Ph

ase

[deg

]

Co

olin

g w

atertem

peratu

re [˚C]

Time [hours]

Cooling water temperature

Phase of 80 MW klystron

Klystron temperature stabilization

Phase variation

Calculated temperature coefficient: 0.74 deg. / ˚C

2.4 deg.

3 ˚C

< 0.5 deg.

< 0.5 ˚C

Control Induction Voltage Regulator (IVR) to compensate line voltage variation

Optimization of de-Q'ing rate 7% 4%

Improvement of modulater regulation

0.3 % (rms)

0.03 % (rms)

PFN voltage

24

25

26

��

��

��

Vdc

Vpfn

Vdc

Vpfn

00:007/3

00:007/2

00:007/1

±0.29% rms

±0.03% rms

24

25

26

��

��

��

Vdc

VpfnVdc

Vpfn

00:005/23

00:005/22

00:005/21

±1.1% rms

±0.08% rms

2 days2 days

IVR AC to DC De-Q'ing PFNAC PFN Voltage to PulseTransformer

[kV

]

[kV

]

[kV]

[kV]

-1

-0.5

0

0.5

1

0 1 2 3 4

Bea

m e

ner

gy

[%]

Time [hours]

0.06 % (rms)0.4 % (peak to peak)

Improved beam stability

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10

Bea

m i

nte

nsi

ty

Time [hours]

1.9 % (rms)

0.03 % (���) (10 min)

> 1 % (10 h)

0.06 % (���) (4 h)

Beam energy

> 20 %

1.9 % (rms)

Beam current

1 Stabilization of RF amplitude & phase Investigate variation chains

Stabilization of their origins or devices 2 Reduce beam loading fluctuation

Synchronization of linac RF with ring RF3 Compensate accidental energy variation

Introduce Energy Compression System (ECS)4 Reduce residual beam position drift

Introduce feedback control

No SHB!

Strategy for stabilizing beam energy

Asynchronous RF issue before 2001

0.5% 1% 0.5% 1%

Asynchronous 2856-MHz RF forms two or three bunches along with beam trigger timing referred to the RF phase.

Energy distribution of 1-ns beam (@1.9A)

Ring 508.58 MHz Linac2856 MHz

Counter

NoSub-harmonic

buncher1-Hz beam

triggerAsynchronous

relation

Unstable beam energy at high current Unstable current of single-bunch beam

New synchronous oscillator

Ring MasterOscillator508.58 MHz

Counter

Arbitrary WaveformGenerator

Band PassFilter

± 5 kHzExt. Clock

1 pps

Start Trigger

Gun Trigger

2856 MHz

ProgrammedBurst Sine Waves

89.25 MHz

FrequencyMultiplier

x 32

Linac RF system

A start signal synchronous to 508.58 MHz starts the AWG to generate a burst wave of 89.25 MHz

A narrow band pass filter reduces phase noises

290 µs O/E E/O

Beam pulse width : 250 ps

Single-bunch current stability

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120

Beam current after electron gun

Beam current after bunching section

AsynchronousSynchronous

Time (min)

Bea

m C

urre

nt (

A) Instability caused in

bunching section

Beam energy stability at high current

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0 50 100 150 200

Bea

m e

ner

gy

[%]

Time [s]

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0 50 100 150 200

Bea

m e

ner

gy

[%]

Time [s]

Asynchronous Synchronous0.03% rms 0.009% rms

1-ns beam energy at 1.4 A

Strategy for stabilizing beam energy

1 Stabilization of RF amplitude & phase Investigate variation chains

and fix their origins2 Reduce beam loading fluctuation

Synchronization of linac RF with ring RF3 Compensate accidental energy variation

Introduce conventional Energy Compression System (ECS)4 Reduce residual beam position drift

Introduce feedback control

Bunch length

Bea

m e

ner

gy

1 GeV beam3 m long accelerating structureRectangular type bending magnets

Energy Compression System (ECS)

Chicane expands bunch length along with beam energy. ECS compresses beam energy spread and variation. ECS requires RF phase stability

ECS requires RF phase stability

1) PLL circuit for ECS klystron drive system

Phase variation0.2 deg. rms

New synchronousOscillator

Phase variation0.2 deg. rms

ECS Phase instability: 0.3 deg. rmsEnergy instability : ~ 0.01% rms

2 ) Klystron voltage > 350 kV

0

2

4

6

8

10

0 2 4 6 8 10 12Bea

m c

urre

nt@

sync

hrot

ron

[mA

]

Time [minutes]

ECS compressed beam energy spread

3.5%

ECS off

1.4%

ECS on

40-ns beam at 350 mA

Injection enhancement

Strategy for stabilizing beam energy

1 Stabilization of RF amplitude & phase Investigate variation chains

and fix their origins2 Reduce beam loading fluctuation

Synchronization of linac RF with ring RF3 Compensate accidental energy variation

Introduce conventional Energy Compression System (ECS)4 Reduce residual beam position drift

Introduce feedback control

Feedback control of beam trajectory

Beam position drift at the linac upstream Small betatron oscillation Beam position drift at the injection points

Problem: beam position drift

Beam position stabilization at BT lines• Injector part• Linac end• Long BT to the NewSUBARU storage ring

Control steering magnets reffering to BPM data • Position window: 60µm • Response time: a few minutes

Solution: beam position feedback control

Beam Position Feedback Control

Synchrotron

NewSUBARU

Acc. Structure

Chicane Magnets

-10

-8

-6

-4

-2

Hor

izon

tal S

teer

ing

Mag

net [

A]

Time [week]0 1 2 3

Hol

izon

tal S

teer

ing

Mag

nets

[A]

Automatic Steering Control

-0.2

0

0.2

0.4

0.6

0.8

1

Hor

izon

tal B

eam

Pos

ition

[mm

]

Time [week]0 1 2 3

Hol

izon

tal B

eam

Pos

ition

[mm

]

Stabilized Beam Position

Window 60µm

Feedback Control

BPMsSteeringMagnet

1 Stabilization of RF amplitude & phase Investigate variation chains

Stabilization of their origins or devices Energy instability: 0.03% rms

2 Reduce beam loading fluctuation Synchronization of linac RF with ring RF

Energy instability: < 0.01% rms3 Compensate uncontrolable energy variation

Introduce Energy Compression System (ECS) Long and short term stability High current injection

4 Reduce residual beam position drift Introduce feedback control

Position stability: 60 µm

Summary