SYNCHRONIZED BEAM POSITION MEASUREMENT FOR
SuperKEKB INJECTOR LINAC
M. Satoh†, F. Miyahara, and T. Suwada, KEK/SOKENDAI, 305-0801 Tsukuba, JapanT. Kudou, S. Kusano, Mitsubishi Electric System & Service Co., Ltd., 305-0045 Tsukuba, Japan
T. Ofusa, H. Satome, and M. Takagi, KIT, 300-0045 Tsuchiura, Japan
Abstract

The SuperKEKB injector linac delivers the electron
and positron beams of different properties to four
independent storage rings and a positron-damping ring.
The required injection beam energies are from 1.1 GeV to7 GeV, and the amounts of bunch charges are from 0.3 nC
to 10 nC. Especially, the injection beams to SuperKEKB
electron and positron storage rings require the low
emittance and high intensity bunch charge for the nanobeam scheme operation aiming at the peak luminosity of
8x1035 cm-2 s-1, 40 times higher than the luminosity recordof previous KEKB project. The Phase I beamcommissioning of SuperKEKB has already been
completed from February to June in 2016. The Phase II
beam commissioning of SuperKEKB already started inMarch 16th for physics experiment. Towards Phase III
commissioning of SuperKEKB, the stable beam operation
with high quality beam is getting more and more
important for the success of achieving the luminosity goal.
For this purpose, the linac beam handling to keep theemittance as small as possible is strongly required. For
this reason, we developed the synchronized beam position
measurement software for the correlation analysis
between the beam positions and some beam jitter sources.
In this paper, we report the synchronized beam position
measurement system by using around 100 monitors for
the SuperKEKB injector linac in detail.

INTRODUCTION
The KEKB project has successfully completed in theJune of 2010 after more than decade long operation.
During the KEKB operation, the injector linac provided
the different flavors of electron and positron beams tofour independent storage rings; KEKB electron, positron,
PF, and PF-AR rings. The target ring for the beam
injection can be switched within 20 ms since the linac
parameters of timing and low-level rf phase can bearbitrary controlled up to 50 Hz for the simultaneous top
up injection of three rings excluding PF-AR. The
achievement of simultaneous top up injection gave astrong impact on the great success of KEKB project. It
improves the KEKB and PF stored current stabilities up to0.05% and 0.01%, respectively [1].
For the SuperKEKB project [2], the injector linac
upgrade and beam commissioning have been progressedsince the final stage of KEKB project [3]. Figure 1 shows
the layout of SuperKEKB injector linac with the total
length of 600 m. Here, the beam energy at the J-ARC___________________________________________†masanori.satoh@kek.jp

section is decreased from 1.7 GeV to 1.5 GeV since themain ring energy of electron is changed from 8 GeV to7 GeV. It is effective for grabbing a standby klystron inSectorA and SectorB. For the SuperKEKB injector
operation, the most challenging issue is the high bunchcharge transportation of low emittance beam. It isstrongly required to the nano-beam scheme operation of
the main ring for getting the high luminosity. For the highintensity positron generation, the flux concentrator and 10large aperture S-band accelerating structures have been
manufactured and installed into the beam line. As a lowemittance and high intensity electron source, we havedeveloped and installed a new photocathode rf gun cavity
based on a noble new scheme in the summer of 2013. Inaddition, a new laser system has been also developed andworked well [4].

Figure 1: Schematic layout of the SuperKEKB injector
linac. It comprises two strait sections of 120 m and
500 m long. They are connected 180 degree bending
section. The both electron sources of thermionic andphoto cathode rf gun are situated at the most upstream
end of the injector linac.

BEAM POSITION MONITOR READOUTSYSTEMPrevious System
For the stable beam operation, the beam monitors aresignificantly important for getting information of beam
bunch length, transverse profile, bunch charge, beamposition, and so on. The beam position monitor (BPM) is
one of the essential monitor for the accelerator beamcontrol. In the SuperKEKB injector linac, around 100
strip line type BPMs have been installed and utilized forthe daily beam operation and various feedback systems[5].
In the begging of the KEKB project, a first BPM
readout system have been developed for the injector linac.
It was comprised of a VME bus based CPU module witha MC68060 microprocessor of 50 MHz, a digital
oscilloscope, and a cable combiner box. The digital
oscilloscope has the performance with the sampling rateof 5 GHz, the vertical resolution of 8 bits, and the analog

Figure 3: Beam orbit panel developed by Python/Tkscript. The plots show the horizontal (top), vertical(middle) beam positions in the units of mm, and bunchcharge in the unit of nC at each BPM location throughthe electron gun to the end of beam transport line.

Figure 2: Schematic drawing of the previous BPM
readout system by using a fast digital oscilloscope
based on the Windows operating system. One monitor
station is comprised of an oscilloscope and a cablecombiner box. It processes the analog signal fromabout 4 BPMs.
bandwidth of 1 GHz. The CPU module and the digital
oscilloscope was communicated via GPIB bus. The client
software showing beam orbit information can get the dataof calculated beam position and bunch charge from theCPU module via linac control network. The speed
performance of this system is around up to 1 Hz, which islimited by the communication speed of GPIB bus. Thecontrol system software was a in house system based onremote procedure call.
Towards the simultaneous top up injection of KEKB
electron, positron, and PF rings, the beam position
measurement up to 50 Hz was getting important. For thisreason, the new BPM readout system has been developedand installed [6, 7]. We have adopted a WindowsXP
based fast digital oscilloscope with the sampling
frequency of 10 GHz, the vertical resolution of 8 bits, andthe analog bandwidth of 1 GHz. We have continued toutilize the existing BPM heads and cable combiner boxes.
Around 20 monitor stations process the analog signal
from about 100 BPMs. One monitor station calculates thehorizontal, vertical beam positions and bunch charge byusing the analog waveform from BPMs through the cablecombiner box as shown in Fig. 2.
In this system, CH1/CH2 and CH3/CH4 are used forthe low bunch charge modes and the high bunch charge
mode, respectively since it is impossible to change thevertical scale of oscilloscope in every 50 Hz. The low
bunch charge mode from 0.1 nC to 1 nC are utilized forthe light source injection and KEKB electron ringinjection. The high bunch charge operation around 10 nCis utilized as the primary electron impinging on tungsten
target for positron beam production. The control softwareof this system has been developed with Experimental
Physics and Industrial Control System (EPICS)
framework [8]. We have developed the EPICS
Input/Output Controller (IOC) for this system by using
Microsoft Visual Studio 2005 C++, TekVisa, and EPICS
base R3.14.8.2 environments. Figure 3 shows the example
of beam orbit display panel developed by using Python
scripting language. The calculated beam position andbunch charge data can be accessed via EPICS process
variables (PV). These PVs are utilized for many highlevel applications like an energy feedback system. The
repetitive data acquisition speed performance of thissystem is up to around 150 Hz with the data length of 20
k points and simultaneous 4 channels measurement.

Current System
The previous BPM readout system has the beam
position measurement precision of about 50 µm, which isenough performance for the KEKB project. However, thelow emittance beam handling with the high bunch charge
is one of the key goal indicators for the SuperKEKB
injector linac. The precise alignment of accelerating
structures and magnets less than 100 µm is strongly
required to avoid the emittance growth caused by thetransverse wake field effect. The high precision beam
position measurement and control is necessary since highquality alignment is practically much difficult. For thisreason, a new BPM readout system based on VME card
has been developed and installed [9, 10].
The current BPM readout system consists of a VME
CPU of MVME5500, a RAS board, an event receivermodule (EVR), and a BPM readout board with four
analog input channels. The BPM readout board iscomprised of a main FPGA, four sub FPGA, four ADCs
with the sampling frequency of 250 MHz, and the verticalresolution of 16 bits. In addition, it equips three variableattenuators, two band pass filters (BPFs), one low passfilter, two low noise amplifiers, and one calibration pulser
for each input channel. The band pass sampling techniquewith the combination of 4th order Butterworth filter and2nd order Bessel filter can make a high precision beam

position measurement up to 3 µm. It was convinced thatthe beam position measurement precisions of all BPMs
are less than 10 µm. It satisfies with our final goal. The
EPICS IOC as a control software is built by using EPICS
base R3.14.12 running on VxWorks 6.8.3.

SYNCHRONIZED BEAM POSITION
MEASUREMENT SYSTEM
A synchronized beam position measurement system(SBPMS) is developed as the EPICS IOC with the EPICS
base R3.14.12 running on the Linux of CentOS version 5or 6. The SBPMS is monitoring the all waveform typePVs of 23 monitor stations. One waveform PV contains
the horizontal, vertical beam positions, bunch charges of
1st and 2nd bunch for each BPM, the beam shot ID, and soon. The beam shot ID is delivered from the event
generator module (EVG) to EVR installed in the BPM
readout VME chassis. It is a cyclic counter of 16 bits. By
comparing the beam shot ID, the SBPMS can collect only
exactly synchronized beam shot data over all 23 BPM
readout stations.
The SBPMS contains 12 EPICS PVs as follows. (1)and (2) are the waveform type PVs containing the BPM
name information and the description about the datacontaining order in the DATA PV as the string characters.
There are 10 DATA PVs of (3) corresponding to 10
different beam modes. The beam mode identifier is thelast part of PV name which is presented by 3 characterslike KBE, KBP, and so on.
(1)
LIiBM:BPM_SYNC:NAMELIST(2)
LIiBM:BPM_SYNC:PROPLIST(3)
LIiBM:BPM_SYNC:DATA:[BeamMode]
If the SBPMS cannot obtain the updated PV data fromthe BPM EPICS IOC until the predefined timeout value,
the corresponding parts of synchronized beam position
data are filled with zero values. Even in such case, thehigh-level applications can use the updated synchronized
PVs including some zero values.
In the SuperKEKB injector linac, the fast rf monitor has
been also developed and utilized for the daily operation[11]. This monitor also can handle the beam shot ID
provide by the EVG system. The similar synchronizeddata management IOC is now under development about
the rf monitor. We have a plant to compare thesynchronized shot-by-shot data between the BPM data, rf
phase data, and rf amplitude data in the near future. In
addition, the similar framework will be applied to also thepulsed magnet control system [12]. Eventually, thecomparison among the BPM data and the other monitor
system data for each exact same trigger shot could givesome useful information to find the beam jitter origins[13].

CONCLUSIONSThe synchronized beam position measurement
framework is developed for the SuperKEKB injector linac.
This system is the EPICS IOC running on the Linuxserver computer. The similar framework will be applied

to the other systems like the rf monitors and pulsed
magnet controllers. Eventually, the correlation analysis
between the beam position and other data could bring us
the detailed information about the source of beam
fluctuation. It will be greatly helpful for the high quality
beam operation required for the SuperKEKB Phase III
commissioning.

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