< kazuro.furukawa @ kek.jp >Pulse-to-pulse Beam Modulation
andEvent-based Beam Feedback System
at KEKB Linac
K. Furukawa, M. Satoh, T. Suwada, T.T. Nakamura
KEK< kazuro.Furukawa @ kek.jp >May 25, 2010.

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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KEK Electron Accelerator Complex
Linac clientsKEKB Asymmetric Collider
HER 8-GeV e– 1nC x2
LER 3.5-GeV e+ 1nC x2(with 10nC primary e–)

PF 2.5-GeV e– 0.1nC
 PF-AR 3-GeV e– 0.2nC

Improvement efforts at Linac were carried in several
steps

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Contents
Past feedback loops at KEK linac
Simultaneous top-up injections
 Beam instrumentation

Event-based closed feedback loops
Conclusion

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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KEKB Operation Improvement
Belle/KEKMay.2000
Apr.2003
Dual Bunch e+Feb.2005
ContinuousInjections
Dec.2008
Crab Cavities andSimultaneous Injection
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Linac Beam Instabilities at CommissioningBeam instabilities were observed at the beginning ofcommissioning (2000~2005)
 Energy, orbit, energy spread, emittance, charge

Fluctuation source hunting Analysis by correlation, tolerance, single value decomposition, timedependent correlation, etc
 Many of them caused by simple failures of equipment, utility(temperature, power), or design deficiencies
 But it took some time to fix... During that time,Simple and slow beam feedback loops were effective
 Sometime, more sophisticated method like down-hill simplex wasperformed (that may hide the important defects)

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Energy Stabilization
Energy instability was sometimes found Closed feedback loops
were formed
 Beam positions weremeasured where dispersion
function is large
 RF phases at adjacentstations were changed
 Loop parameters were
beam mode dependent Energy spread feedback
using multi-electrode monitor
was also implemented
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Simple Orbit Stabilization
If Orbit became unstable Beam positions were measured where betatron phases are90degree apart Corresponding steering magnets are adjusted
 If the orbit fluctuation was large, weighed average of BPMs
based on response functions to beam kick or energy change The same method was applied to equipment stabilization

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Simple Stabilization Examples
 7-min energy change, later 40-min orbit change, later attributed toattributed to air conditioner
RF source for a buncher cavity
at the 1st high power source

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Implementation and Results
Those closed loops were implemented in a scripting
computer language with graphical user interface
 With separate activity management/monitor panel As standard simple PI (Proportional-Integral) controller

Very effective during commissioning
Instability sources were identified and fixed Became unnecessary later during normal operationEffective during beam study With unusual and scanning beam condition

1Hz measurement at the beginning 50Hz measurement was hoped
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Fast beam switching or Simultaneous Injection
Luminosity degradation on beam studies at PF andPF/ARSensitive luminosity tuning with Crab cavities
Future SuperKEKB injections with shorter lifetime
PF top-up injection for higher quality experiments
CERN/PS switches beams every 1.2s (PPM)SLAC/SLC switched beams at 180 Hz

KEK Linac had switched beams 360 times a day in 2008 (justbefore simultaneous injection)
10~120seconds per switching

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Linac Energy ProfileB	A	C	1	R	

2	3	4	5	Energy(GeV)	

deceleration	

e-: 0.1nC	

2.5 GeV → PF	

1.7	

8.0 GeV → HER	e-: 1.0nC	n	acceleratio

1.7	e-: 10nC	

1.7	

R	Pulse-to-pulse modulation and feedbacke+: 1nC	

3.5 GeV → LER	

end of LINAC	

Kazuro Furukawa, KEK, May.2010.

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Event System Configuration
 MRF’s series-230 Event Generator / Receivers
 VME64x and VxWorks v5.5.1
114.24MHz event rate,
 EPICS R3.14.9 with DevSup v2.4.1
50Hz fiducials
 17 event receivers up to nowMore than hundredCentral"
Event Generator"
50Hz-Analog/Timing data
Multi/single-mode fiber
Timing precision is < 10ps.
SH_A1"
Injection"

KL_B5/B6"

ARC!

SB_B"

SB_A"

 < 1ps with external module.

e­	  Gun!

e– BT (PF: 2.5GeV, 0.1nC)!

Cont-ABC"
KL_51/52"
SB_C"

SB_1"

SB_2"

SB_3"

SB_4"

SB_5"

e+ BT (KEKB: 3.5GeV, 2nC)!	  

e+	  Target
Cont-1"

Cont-2"

Cont-3"Cont-4"Cont-5"

Event Receivers"
Pulse-to-pulse modulation and feedbacke– BT (KEKB: 8GeV, 2nC, !
PFAR: 3.0GeV, 0.1nC)!

Kazuro Furukawa, KEK, May.2010.

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Linac Event System
Satisfies the requirements
Event rate : 114.24MHz (bit rate : ~2.3GHz)
Fiducial rate : 50Hz
Timing jitter (Short term) : ~8ps
No. of defined events : ~50
No. of receiver stations : 17
No. of Fast parameters : ~130

CPU
EVG
EVR
Opt. Fan-out

EVR & LLRF

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Event Manipulation
Human Operator

Injection Programs

Arbitrate and Generate Beam Mode Pattern (in PythonTk)
considering priorities of the rings
equalizing pulsed power supply intervalin 4 arrays (waveforms) of length 2 (40ms) to 500 (10s)each element corresponds to a 20-ms time slot and a beam mode �Generate Events for the Next 20-ms Time Slot (in Event Generator)
reading two consecutive elements from the beam mode patterngenerate several events for the next pulse
generate preparation events for the next after next�

Generate Signals based on Received Events (in Event Receiver)generate pulsed signals as prepared in the previous time slot
program the signals (enable/disable, delays, etc) for the nextstart to generate analog signals for the next�Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Beam Mode Pattern Generators
 Pattern panel arbitrates requests
 From downstream rings with priorities, or human operators
 There are several pattern rules due to pulse device features andlimitations
 Pattern arbitrator software was written in scripting languages to meet
daily changes during the commissioning stage
Remote controlled automatic pattern arbitrator"

Manual pattern generator"

Recent typical operation.
~37Hz for KEKB LER
~12.5Hz for KEKB HER
~0.5Hz for PF
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Parameters
Parameters switched via event system
LLRF phase/timing : 14x4
Overall energy profile, dual-bunch energy equalization, final energy adjustment

HP RF timing : ~60
Energy profile and backup management

Gun voltages, picosecond delay : 4
Beam charge selection, dual bunch selection, bunchingPulsed magnets/solenoid : 14
Beam transport selection, orbit controls, positron focusing

Injection phase interface : 2
Bucket selection interface : 2
BPM : ~100x3

Sufficient for fast beam mode switchingIntegrity monitors soon
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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BPM
Tektronix DPO7104 can acquire data at >=50Hz
With embedded EPICS

Beam modes are recognized by events through CA network
Clients can monitor data of an interested beam mode
26 oscilloscopes are installed
100 BPMs are synchronized. (100 BPMs at BT as well soon)

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Measurement and Data Acquisition
Originally much efforts to developdetectors, shaping amplifiersNo budget for all BPMs

Switched to direct waveform acquisition
Minimized active components, then minimized
calibration tasks, maintenanceEqual-length cables
One oscilloscope covers about 5 BPMs, orcombined 20 (or 40) waveforms
5 - 10Gs/s (with additional interpolation)
Possible to measure dual bunches
Solved many issues at once!
Extract each signal, apply calibration factors,
send to upper layer at 50Hz

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Simultaneous Top-up Injection Results
Beam currents
are kept withinKEKB 1mA (~0.05%)
PF 0.05mA (~0.01%)

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Three Virtual Accelerators
 Controls and instrumentations are essentially mode-dependent, andmutually independent Selecting a real machine out of three virtual machines Managing three parameter setse− Gun!
ARC!

e– BT (PF: 2.5GeV, 0.1nC)!

PF Injection�
e+ Target

Event-based
Control System"e− Gun!
ARC!
Primary e–KEKB-LER Injection�
(4GeV, 10nC)

e+ BT (KEKB: 3.5GeV, 0.6nC)!

e+ Target"e− Gun!
ARC!

KEKB-HER Injection�
e+ Target"e– BT (KEKB: 8GeV, 1.2nC)!

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Combined Event-based Feedback Loops
Simultaneous injections are managed byindependent parameters for three virtual
accelerators of KEKB-HER, KEKB-LER and PF
On each of virtual accelerators, closed
feedback loops for energies using the sameprocedure were installedAs parameters are independently managed,
no modification to the software wasnecessary
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Three-fold Independent Closed Loops Feedback loop software act on one of three virtual machines Managing independent parameter setse− Gun!
ARC!

e– BT (PF: 2.5GeV, 0.1nC)!

PF Injection�
e+ Target"e− Gun!

Event-basedControl System

ARC!
Primary e–

KEKB-LER Injection�
(4GeV, 10nC)

e+ BT (KEKB: 3.5GeV, 0.6nC)!

e+ Target"e− Gun!
ARC!

KEKB-HER Injection�
e+ Target"e– BT (KEKB: 8GeV, 1.2nC)!

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.22

Results and Future No signs of instabilities up to now (other than white noise) No fast oscillation was observed with 50Hz measurement
 Event-based feedback loops may be useful during beam
study, or when some equipment or utility became unstable Orbit feedback loops should be applied with pulsed steering
magnets. Also energy-spread stabilization may be possible
 In the future SuperKEKB project, when new equipment will beinstalled, event-based feedback loops should be necessary
 Fast processing implemented in a compiler language is underdevelopment

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Conclusion
Closed beam feedback loops for beamcharacteristics were useful under certain condition
Pulse-to-pulse modulated simultaneous injection
improved the experiment performanceEvent-based feedback loops were implemented
Feedback system will be necessary in the future
project with additional equipment
 Acknowledgement: Event-based controls was not possible without
help from EPICS community. Thanks to them all over the world.
Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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Thank you

Pulse-to-pulse modulation and feedback

Kazuro Furukawa, KEK, May.2010.

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