InternationalInternational
Conference
Conferenceon Accelerator
on Accelerator
and LargeandExperimental
Large Experimental
Physics Control
PhysicsSystems,Control1999,
SystemsTrieste, Italy

DATA ACQUISITION OF BEAM-POSITION MONITORSFOR THE KEKB INJECTOR-LINAC
Norihiko Kamikubota, Tomonori Obata*, Kazuro Furukawa and Tsuyoshi Suwada
High Energy Accelerator Research Organization (KEK)
1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
Mitsubishi Electric System and Service Co. Ltd. *Umezono 2-8-8, Tsukuba, Ibaraki, 305-0045, Japan
Abstract
About 90 stripline-type beam position monitors (BPM)
have been installed for the KEKB e-/e+ injector-linac. Adata acquisition system for the BPM has been developed.
It is comprised of two Unix workstations and eighteen dedicated front-end systems (VME computers and digital oscilloscopes). The BPM waveforms, detected by a digital
oscilloscope, are analyzed by a VME computer, then thecalculated beam parameters (beam current, x-position, yposition) are transferred to workstations using the UDP
protocol. The workstations are used as data servers forclient applications. The present data acquisition system enables a real-time indication of the beam parameters over thewhole linac.

1Application(Unix, PC)
BPM
BPM
application
application

BPM
application
BPM
BPM
application
application

TCP
protocolData server(Unixworkstation)
shared memory
for BPMfor
Frontend #1

TCP
protocolBPM
data server
Read shared memory
for BPMfor
Frontend #18

...

for
Frontend #1

BPM
data server
Read...

Write

INTRODUCTION

2 DATA-ACQUISITION SYSTEM
Overview

UDP
Front-end
VME #1 send protocol(VMEOS-9)
Readsharedmemory BPM
for BPM data

for
Frontend #18

Write

recv

The KEKB (KEK B-factory) project, which aims to investigate CP violation in the decay of B mesons by an asymmetric electron-positron collider, is now undergoing accelerator commissioning. As a part of the KEKB project, thee-/e+ injector-linac [1, 2] has been upgraded to provide single bunch beams of 3.5 GeV positrons and 8 GeV electrons
directly to the KEKB rings. The beam currents (design values) are 0.64 nC/bunch and 1.3 nC/bunch for positrons andelectrons, respectively. In addition, high current electron
beams (10 nC/bunch) are required to produce a sufficientamount of positrons. In order to suppress any beam blowup
generated by a large transverse wakefield, a real-time monitor for beam orbits is indispensable.
We developed a data acquisition system for the beam position monitors in the KEKB e-/e+ injector-linac. It has
been extensively used during the commissioning of theKEKB accelerators since December, 1997. In this article, detailed descriptions of the data acquisition system aregiven in Section 2, and discussion follows in Section 3.
Some other subjects (i.e. design of the monitor, calibration
coefficients determination, etc.) are given in [3, 5].

2.1

4, 5]. The data acquisition system comprises two1 Unix
workstations and eighteen2 dedicated front-end systems.
An overview of the data acquisition system with important
control processes and data flow is shown in Fig. 1.

recv

VME #2

UDP
protocol

VME #18

Write
BPM
waveform read-out
from oscilloscope

Figure 1: Overview of the data-acquisition system.

2.2

Front-end

The eighteen front-end systems are located in the linac
klystron gallery at a nearly equal interval along the beamline. Each front-end system controls 3–12 BPMs (12 atmaximum). Fig. 2 shows a schematic drawing of a frontend system. It is comprised of a VME computer (the OS-9operating system with a 68060 microprocessor at 50 MHz),a digital oscilloscope (Tektronics TDS680B) as a signal
digitizer, and two signal combiners in a box.
The four signals of one BPM are fed to two signalcombiners (vertical and horizontal) together with the sig-

About 90 stripline-type beam position monitors (BPM)
have been installed at the KEKB e-/e+ injector-linac [3,217

1 To be three after September 1999. See 3.2.
2 Since June 1999, there are nineteen.

nals from other BPMs. Delay cables (7ns) are used to avoid
waveform overlaps at the signal combiners. The two combined signals are digitalized by an oscilloscope at a sampling rate of 5 GHz. The digitalized signals are analyzed by
a VME computer in order to deduce the beam parameters(beam-current, x-position, y-position), taking into accountthe calibration coefficients.3

GPIBDigital Oscilloscopey x
5GHz Sa/s

VME/OS-9

Combiner Box
8ch-Combiner*

8ch-Combiner*

Klystron Gallery
35-m-longcoaxial cableBPM

Linac Tunnel

2.4

BPM Applications

All of the BPM applications receive the latest beam parameters by sending requests to one of the data servers.
This communication is made with the TCP-protocol using the standard format of the injector-linac control system.
Typical response times are 1–10 ms, depending on the CPU
power of the application side computer.
Some applications with real-time graphical presentation
have been developed. An example, which runs with theX-window environment, is shown in Fig. 3. This application can show the positions (x and y) and beam-currentsof the entire linac with a refresh interval of 2–5 seconds.
It is interesting that the graphic part of the application isgenerated by using the resources of the SAD computers4
at the KEKB-ring control system. Thus, this is an example
of successful communication between two different controlsystems.
More important applications of the BPM are feedbacksof the energies and the orbits. The feedback applications
have been developed in order to suppress beam instabilities over long-term operation. As of July 1999, there areroughly 20 feedback applications, and among them 10 arealways running during normal operation [10, 11].

*Delay Cable (7ns)

Figure 2: Schematic drawing of a front-end system.
Trigger pulse signals, which are synchronized with thelinac beam, are provided to all front-end systems at 0.7 Hzcycle. These signals are used to start the data taking cycleof each front-end system. The trigger rate is limited by theGPIB communication throughput between the VME computer and the oscilloscope.

2.3

Figure 3: Example of a graphic application of the BPM.

Data Servers

Calculated beam parameters at a front-end are transferredto the Unix workstations with the UDP protocol, wheredata servers are available (see Fig. 1). The workstations are
the same ones for the injector-linac control system [6, 7].
Two data servers have been prepared to realize higher redundancy, as well as to distribute the CPU loads over the
existing workstations. In order to reduce the network traffic, data transfer is done when the beam positions and currents are renewed at a front-end. As a result, the traffic rate
between the front-end systems and the Unix workstations
is always constant (25 frames per second, 0.7 Hz x 18 x 2).
Unix workstations store the most recent ten data setsfor each front-end in shared memory. The data server returns averaged values by using this cached data. The use ofcached data greatly decreases the total amount of the network traffic and the workstation CPU load.
3 Detail description on the calibration coefficients is given in [3, 5].

3 DISCUSSION
3.1

Performance

Though the injector-linac can be operated at 50 pps(pulses per second) at maximum, the data-acquisition rateof the present system is 0.7 Hz (see 2.2).
The position resolutions have been measured using single bunch electron beams [3, 5]. The measured values are
0.12 mm for a beam of 1 nC/bunch, and 0.098 mm for
7 nC/bunch, respectively. These values agree well with thedesign value (0.1 mm).
4 SAD, Strategic Accelerator Design, is a computer program complex
for accelerator design. It has been developed in KEK since 1986. See [8]for more detail.

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3.2

Operational Experiences

The present data acquisition system has been sufficiently
stable since December, 1997. During the KEKB commissioning in 1998-1999, many BPM applications (see 2.4)
were developed. They are now indispensible for both theoperators and the commissioning staff to achieve highly
stable beam supplies for the KEKB rings.
During operation in the first half of 1999, we have experienced very high CPU consumption rates on the Unix
workstations, because too many BPM applications (especially feedback applications) were invoked at the sametime. We have rearranged the feedback applications so as
not to consume so much CPU power (i.e. set the iterationintervals longer). In addition, a new Unix workstation wasintroduced in August, 1999, in order to increase the total
CPU power. This third workstation will be used for operation very soon [9, 10].
Occasionally (typically once a month), due to long-term
jitter of the trigger signals for the oscilloscopes, the system becomes unable to analyze BPM waveforms. In sucha case, we control the main source of the trigger signals tocancel the jitter.

3.3

The applications of the BPM have been acknowledged to
be fundamental tools for the commissioning of the KEKB
accelerators. The real-time monitors are essential for successful beam handling, and the feedback loops are inevitable to suppress beam instabilities over long-term operation.
The number of BPM transactions is increasing year byyear. The amount reached as high as 158 transactions per
second in June, 1999. The use of cached data is efficient todecrease the network traffic and the CPU loads in total. In
addition, we introduced a new workstation to increase thetotal CPU power.

5 ACKNOWLEDGMENTS
The authors acknowledge Prof. K. Nakahara and Dr.
H. Kobayashi for kindly supervising our work. We thankDr. H. Koiso for developing the graphic application of theBPM. We also thank the KEKB and the linac commissioning group for encouraging our work.

Transactions

6An analysis of the log files produced by the BPM dataservers enables us to determine how many transactions persecond (data requests) arrived at the data servers. Table 1
gives the expansion of BPM transactions during the recent
KEKB commissioning period.
In June, 1999, the BPM servers accepted 158 transactions per second, while the total transactions for all the accelerator devices (including klystron modulators, magnet
power-supplies, vacuum pumps, and so on) was 230. This
amount (230) corresponds to 700 network frames per second, and 90 kB/s data transfer over the control network [9].
We consider that such a high transaction rate has been possible with the use of cached data at the data servers.
Table 1: Expansion of the BPM transactions.
time
Dec.1997
Jun.1998
Dec.1998
Jun.1999

REFERENCES[1] I. Sato, et. al, KEK-Report 95-18 (1996)[2] A. Enomoto, Proc. XVIII Int’l Linear Accelerator Conference(Linac’96), Geneva, August 1996, CERN 96-07 (1996) p.633[3] T. Suwada, N. Kamikubota, K. Furukawa and H. Kobayashi,
Proc. the 8th Beam Instrumentation Workshop, Stanford,May 1998; KEK-Preprint 98-48[4] T. Suwada, N. Kamikubota, K. Furukawa and H. Kobayashi,
Proc. of the First Asian Pacific Accelerator Conference(APAC98), Tsukuba, Japan, March 1998, KEK-Proceedings
98-10 (1998) p.531[5] T. Suwada, N. Kamikubota, H. Fukuma N. Akasaka andH. Kobayashi, “Stripline-type beam-position-monitor system
for single-bunch electron/positron beams”, Nucl. Instr. Meth.
A, in press; KEK-Preprint 98-236[6] N. Kamikubota, K. Furukawa, K. Nakahara and I. Abe, Nucl.
Instr. Meth. A352(1994)131

Transactions
0 trans./s
35 trans./s
62 trans./s
158 trans./s[7] N. Kamikubota, K. Furukawa, K. Nakahara, I. Abe andA. Shirakawa, Proc. Int’l Conf. on Accelerator and Large
Experimental Physics Control Systems (ICALEPCS’95),
Chicago, October 1995, FERMILAB Conf-96/069 p.1052[8] http://www-acc-theory.kek.jp/SAD/sad.html[9] N. Kamikubota, K. Furukawa, H. Kobayashi, K. Nakahara,
T. Suwada and T. Urano, Proceedings of the 24th Linear Accelerator Meeting in Japan, Sapporo, July 1999, (1999)p.119121 (in Japanese)

4 CONCLUSION
We developed a data acquisition system for the beam
position monitors at the KEKB injector-linac. The system
has been extensively used since December, 1997. The dataacquisition rate is 0.7 Hz, which is limited by the GPIB
communication throughput of a digital oscilloscope.

[10] T. Suwada and the KEKB commissioning group, Proceedings of the 24th Linear Accelerator Meeting in Japan, Sapporo, July 1999, (1999)p.22-24 (in Japanese); KEK-Preprint
99-43[11] K. Furukawa, et. al., “Energy Feedback Systems at KEKB
Injector Linac”, this conference

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