BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Beam Feedback Systems andBPM Read-out System
for the Two-Bunch Acceleration
at KEKB Linac
Kazuro Furukawa
andNorihiko Kamikubota, Tsuyoshi Suwada, Tomonori Obata(KEK)<URL:http://www-linac.kek.jp/>

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Introduction
u Experiment Efficiency of CP Violation Studyat KEKB Electron / Positron Collider—> Now Electron 780mA, Positron 1200mA
2.6A Positron will be Stored—> Especially Quality and Quantityof Positron is Importantu Linac : 8GeV e- 1.28nC / 3.5GeV e+ 0.64nC 50pps
u Multi-Bunch Acceleration at Linac—> Integer Relation 2856MHz : 508MHz = 275 : 49 in rf System
Common Frequency 10.38MHz = 96.29ns (Bunch Separation)—> Only 2 Bunch Possibleu Stable 2 bunch Acceleration—> Longitudinal and Transverse Wakefield Effects
Should be Managed
K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linacu Upgrade of Beam Instrumentation—> Should Observe Both 2 Bunches Simultaneously—> Should not Lose Accuracy for 2 Bunches Separated 96ns
u Wire Scanner—> Split the Signal and Read ADC with the Separate Gate—> Possible to Measure the Emittance of Each Bunchu Streak Camera—> Observe with Separate Timing—> Possible to Measure the Longitudinal Bunch Structureu Beam Position Monitor (BPM)—> Necessary to Read-out 90 Stripline-type BPMs—> Need to Process Two Signals Separated 96 ns

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Read-out System of BPMs
u 18 Measurement Stations along the 600-m LinacConnected with 4 - 10 BPMs
(90 in Total)

Sector B

180-deg.
ArcSector C

Sector A

C-Gun

A-Gun
Positron Source

Sector 2

Sector 1

ECS
Sector 3

Sector 4

Sector 5

PFKEKB

Beam Switchyard

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linacu Signal Processing—> Avoid Overlap with Delay-lines—> Overlay with Combiner—> Waveform Digitization
with Oscilloscope (2ch 5Gs/s)
u Timing Trigger—> Beam Synchronized Trigger
along the Linac by 571MHz rf
u Pre-process with VME Computer—> Adjust Dynamic RangeAccording to Beam Mode
(Sometimes x1 -> x30)—> Read thru GPIB—> Locate and Process
Each Signal in the Waveform

Oscilloscope (5GS/sec)
1st BPM
2ndCh.2
Right

Left
Right

Left

Ch.1

UpUp

Down
Down

Combiner
16ns Delay x 4

Combiner
16ns Delay x 4

Right

Left
Down

Up

1st BPM

2nd BPMBeam

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Improvement for 2-Bunch Accelerationu Acquire 2 Beam-bunch Information in One rf Pulse—> Difficult with Dedicated Electronics(Challenging Issue for Next 50Hz Read-out System)—> Easier with Oscilloscope
Waveform becomes Shifting and Overlapping by 96ns
u Overlap of Signals
Each Signal is 5ns in Full-width, 1ns Peak-to-peak—> Pack Signals down to 8ns
Sometimes Add Delay Linesu Read Resultant Non-overlapping Signals thru Oscilloscope

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linacu Apply Calibration Information
Mapping Function of 3rd Order Polynomial (BPM)
Attenuation Factors of Cables and Oscilloscope
Position Offsets by Beam-based Alignment
Database was Expandedu Server Computers—> Read all Measurement Station thru Network—> Collect 2-Bunch Data of all 90 BPMs in One Shot, Every SecondCommands were Added
u Many Piece of Operation Software—> Many Beam Feedback Loops andOrbit Displays, etc.
—> Read Once in 1 - 5 Second from Server

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Example Operation Softwareu Many Software Panels are Usedin Beam Study and Operationu Energy Measurement at Buncher Exit
Electron Energy Measured
Changing a Steering Magnet
After Adjusting Gun Timing
First Bunch: 15.5MeV
Second Bunch: 15.8MeV
Almost Equal, Good Reproducibility

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Beam Feedback Loops
u More than 30
Software Feedback Loops
u Energy Feedback
Beam Position

Beam - rf Phaseu Orbit Feedback and Others
Beam Orbits
Steerings

Weighted Average of BPM'sK.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

1st and 2nd Bunch Energy
Two-Bunch Acceleration
1Loading compensation 2.5%

u Relation between
Energy vs. rf Timing

0.99

Relative Energy [%]u Loading Evaluation
Comparing Beams
of 8nC & 0.8nC

Second bunch

0.98

0.97

First bunch
96.29 ns

0.96

0.95-100-50050100

Gun/SLED Timing [ns]K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

New Feedback for Energy Equalizationu Need to Equalize Beam Characteristics of Two Bunches
Suppress Difference of Beam Characteristics from Wakefields
u Energy Difference from Longitudinal Wakefields
Change Energy Gain
Read Beam Position (x and δx)
by rf TimingBeamat Reference Points
BeamFluctuation
BPMBPMof SLED (Energy Doubler)
Klystron Klystron––> Convert into Timingsfor Energy Doublers

Beam Positionsof 2-Bunches
BPMs– Beam Fluctuation––> Convert into Energy
Difference
Average (Integration)
x Gain – Offset

Energy Difference Feedback
K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Successful Acceleration of 2 Bunches (Blue and Green)

Horizontal Orbit

Vertical Orbit

Electron Charge

Positron Charge

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB LinacConclusion
u For 2-bunch Operation of KEKB Injector Linac
Built 2-Bunch Simultaneous Read-out Systemof 90 Beam Position Monitors
u Indispensable to UnderstandDifferences of Beam Characteristics of 2 Bunches
u Many Operation Software Panels Have Been Built
u Beam Feedback Systems
Extended Orbit / Energy Stabilization
Installed New Energy Equalization
Essential for Beam Operationu Now Carrying Beam Study for Injection into KEKB Ring
K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Thank you ...

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Design Beam and Achieved Performance(1) Gun(2) Buncher(3) Arc(4) e+ target(5) e+ Solenoid exit
(6) Linac end

EnergyIntensity
Pulse width
EnergyEnergy spread (σ)
Intensity
Efficiency
Emittance γβε (σ)
Bunch width
EnergyEnergy spread (σ)
Jitters (p-p)
Drift (with feedback)Emittance γβε (σ)
Transmission
EnergyIntensity
Transmission
Intensity
Specific yield
EnergyEnergy spread (σ)
Intensity
Specific yield
Transmission
Emittance γβε (σ)
Pulse repetition

keVnC/pulse
ns
MeV
MeV
nC/pulse
mm
ps
GeV
MeV

8-GeV electron
Goal Achieved
200200
1.5
22
1.8
1616
1.40.06
51.5
0.6%

mm

0.17
100%

GeV
nC/pulse
nC/pulse
e+/e-GeV
GeV
MeV
nC/pulse
e+/e-GeV
mm
pps

1.9
95%
0.04
6
1.7
0.29%

80.15%
1.28>80.05%
>1.28

0.25
50>80%
0.31
50

3.5-GeV positron
Goal Achieved
200
200
13142
2.8151522>10
1190%
0.06
0.08
16101.5
1.7
0.6%
0.38%
0.1%
<0.2%/h1.7>95%100%
3.73.7>10
1096%
2.4
6.8%
3.5>3.5
0.125%
0.15%
>0.64
0.82
2.3%
1.550

1.450
K.Furukawa

BPM-Readout and Beam-Feedback Systemsfor Two-Bunch Acceleration at KEKB Linac

Four Beam Modes at KEKB Linac
u4 Downstream Rings Require Quite Different Beams
u Switching Reproducibility and Reliability are Crucial
u 7300 hours of Operation in FY1999
But Only 73 hours of Beam Loss Time
RingParticle
EnergyChargeHERLERPFARelectron positron electron electron
8GeV 3.5GeV 2.5GeV 2.5GeV
1.28nC 0.64nC 0.2nC
0.2nC(primary10nC)
Bunch
singlesingle1ns
1ns
Repetition 50Hz
50Hz
25Hz
25Hz
Store
500mA 700mA 400mA 40mA
Time
1-2min 5-10min 3-5min 2-5min
Interval
1-2hr
1-2hr
24hr
2-4hr
K.Furukawa