CONTROL SYSTEM FOR A BUNCH/PROFILE MONITOR
AT THE KEK e+/e– LINAC
Kazuro Furukawa, Atsushi Enomoto, Yujiro Ogawa, Satoshi Ohsawa, and Takuya Kamitani
National Laboratory for High Energy Physics (KEK)1 – 1 Oho, Tsukuba, Ibaraki 305, Japan
Abstract
An elaborate beam-monitoring system is indispensable in order to realize stable operation of the electron/positron linac with high-current beams for KEKB. In
this connection we have provided a brief accommodation
for the control system of a bunch/profile monitor employing optical transition radiation (OTR).
In order to utilize the excellent features of the OTR
monitor, it should be associated with an adequate control
system for such components as optical/timing devices anda streak camera.
Since the components had not been designed integratedly, we had to bring them together so that they canwork as a single monitoring system. The components wereconnected to the operator console through Ethernet, GPIB
and serial lines. The software was designed to organize separate devices into a single control object. We developed agraphical user interface on X-Window. The entire system
works satisfactorily and serves as an effective tool for beamdiagnosis.

Introduction
In the next KEK B-factory project (KEKB) [1] theelectron/positron linac at KEK should provide beams with
better quality and stability in order to achieve a higher
luminosity in the ring. Extensive studies must be carriedout in order to understand the beam characteristics withimproved beam energy and current.
The injector section, which comprises a subharmonic buncher, prebunchers, and a buncher, is oneof the most crucial parts for studying the beam characteristics. It is therefore important to simulate the beam
behavior on computer codes, and to measure the transverse/longitudinal distributions of the beam in this region.
Due to the benefit of a fast time response, the combination of optical transition radiation (OTR) and a streak
camera becomes a good system for investigating the longitudinal behavior of the beam. The OTR monitor serves
not only as a beam-bunch monitor, but also as a beamprofile monitor without a halo.
However, the number of such instruments is usuallysmall, or only one, and it normally requires special configurations. It is therefore not economical to design an interface for a single piece of equipment, and such instruments

often are not accompanied with reasonable remote-control
systems, although it is useless without a control system.
In this paper we describe the control system for the
beam bunch/profile monitor which was built without designing dedicated hardware. This may be a typical casefor such a measurement system.

System Description
Transition Radiation Monitor
The transition radiation monitor was intensively investigated at the KEK linac, and showed good results [2].
It comprises a polished stainless-steel radiator, a radiatormover, an optical system, a CCD camera, a timing anddelaying system, and a streak camera. The CCD camera
provides a video signal for the beam profile, and the temporal analyzer of the streak camera provides analyzed datafor beam-bunch information.
We use a streak camera (Hamamatsu Photonics
Ltd., C1587) having a time resolution of 2 ps. The details of the monitor and its performance have been given
elsewhere [2].
Since the distance between the radiator and thestreak camera is large, the optical system must be precisely aligned in order to gather radiation light. Two setsof three-axis movers were installed in order to resolve thisproblem. These movers are used to precisely align lightguiding lenses.
An accurate adjustment of the beam trigger is also
necessary in order to acquire data with multiple bunches
without jitters. We use a coarse delay which is synchronized to the linac rf frequency, and a fine cable delay having
a minimum step of 30 ps.
Control System Design
Since each component for the monitor has not been
designed integratedly, it is important to bring them together so that they comprise a single monitoring system
when it is viewed from the operator side. The system wasconstructed while associating the components with eachother.
The part for the beam-profile monitor, which comprises a radiator mover and a CCD camera, is controlled
by a normal profile-monitor control system. An entry wasmerely added to the system database table so as to enable
this monitor. The OTR monitor shows a greater linearBeam Trigger 476 MHz Clock

CAMAC
Interface

OTR

OpticalSystem

TemporalAnalyzer

StreakCamera

Table 1: List of the components of the bunch-monitor system and their interfaces.
InterfaceRS232C
RS232CGPIB–CAMAC
GPIB
GPIB & RS232C
RS232C

Each component has either a serial line (RS232C)
or a general-purpose interface bus (GPIB) interface. Components which have RS232C interfaces are connected witha terminal server, which accepts host-computer initiated
TCP/IP connections. Instruments having GPIB interfaces
are attached to an Ethernet–GPIB gateway box.1 A system block diagram is presented in Fig. 1.
The monitor is operated at the linac console room.
Most of the software runs on a Unix workstation of the accelerator control system, and an interactive user interfacehas been provided on the X-Window server, as shown inFig. 2.
Software Design
Since the RS232C and the GPIB are not reliable
compared with other parts of the control system, greatcare has been taken to handle any failure recovery and toavoid a deadlock situation. For this purpose, our TCP/IP
1 We use ET488 from Sony Tektronix Inc., which gateways theGPIB and TCP/IP on Ethernet.

RS232C

RS232C

RemoteController

The linac control system was designed as softwareand hardware components that are interconnected withInternet-protocol (TCP/IP) networks [3]. The bunch monitor was also designed so as to connect with the control network, converting the equipment-specific interface of eachcomponent. Table 1 lists the components and their interfaces.

GPIB
GPIB Interface

GPIB

Component Interconnection

Component
Optical System
3-axis mover for lens 1
3-axis mover for lens 2
Trigger Systembeam synchronous 2.1ns delay
30ps fine delay
Streak Camera Systemtemporal analyzer
remote controller

2.1nsDelay

30ps
Delay

3-AxesController

Terminal
RS232C

Control Network - Ethernet - TCP/IP

response compared to our alumina profile monitors. Theprofile can be examined by an image analyzer at the operator’s console.
For the beam-bunch monitor part, since the number of monitors is only one, we did not design a dedicatedcontroller. Instead, we built a system with commerciallyavailable hardware and the software library which has already been developed and used for the linac accelerator
control system.

Server

RS232CNTSC - Video

3-AxesController

Fig. 1: Block diagram of the bunch-monitor components inthe control system. The optical, timing and streak-camera
systems are connected to a control network.
Control Network - TCP/IP - Ethernet
From/To
Equipement

UserInterfaceUnixServer
Computer

X-Window
Display(X-Terminal)

Data Processingand Controls
Video - NTSC
Analyzer Information

VideoDisplay

Fig. 2: Operation of the beam-bunch monitor from thelinac console room.
socket library routines, which reasonably handle time-out
and other failures, were used [4].
The software library for the GPIB was written so
as to be compatible with those on Unix workstations andVME systems, so that it can be adopted for other applications. If the situation changes, we can even replace thehardware for the bunch monitor with the VME system.
However, the software for the RS232C interfaces could not
be made compatible with those on other systems becauseof failure-recovery procedures.
Since the configuration of this type of monitor may
change frequently, we designed the software in an objectoriented way. Each component was built so as to be able
to behave independently, so that each software component
can be easily replaced. However, at the same time, the entire assembled software is intended to form a single objectof a bunch monitor.
In order to make the operator’s manipulation easier,the software components were designed so as to exchange
information with each other. For example, precise calibrations of two beam-trigger delays, and the delay inside thestreak camera, which depends on the sweep ranges, aretreated consistently within the system.
Operator User Interface
In order to build prototypes of the graphical operator interfaces quickly, we used Tk toolkits for the XWindow system [5]. This has enabled us to make user interfaces to equipment very quickly. Figure 3 is an exampleof the interface windows.

Fig. 3: One of the graphical user interface panels on XWindow to control the bunch monitor system. This wasbuilt using Tk toolkits.
Since we can not spend much effort on each single
system, we need well-designed graphical user interfaces.
Tk toolkits are suitable for such applications as beam studies. Further, it can make complicated graphical applications simple. In addition, the event-driven structure of
the language system is appropriate for the control-system
software.
Since Tk follows the Motif look-and-feel criterion for
the graphical user interface standard, it meets our needs.
However, since Tcl language, on which Tk is based, is nota standard computer language, we have not yet decided
whether Tk is appropriate for use in normal control applications.

Discussion and Conclusions
We could build a reasonable control system for ourbunch monitor in a short term by employing commerciallyavailable hardware components, object-oriented software
design and Tk prototyping toolkits for the user interfaces.
This enables us to efficiently study the beams.
This method to build a simple control system may
be applied to minor measurement systems, which may beinstalled in order to improve the linac operation for KEKB.
However, points to be considered still remain. Firstof all, we must connect and monitor the interlock systemof the CCD device in the streak camera. We have not yet
found any proper devices for it. Without interlocking it
may be easily spoiled.
Not all data-manipulation methods which are available on the temporal analyzer are provided on a workstation yet. Since such methods as Fourier transformations
are often useful for understanding the beam characteristics,
we should implement them and provide a user interface tothem.
The GPIB gateway that we used is suitable for isolated GPIB equipment. More GPIB instruments for special measurements will be used in the future. They can bereadily installed in the control network using GPIB gateways. They are also inexpensive, compared with VME
crates with a GPIB board. However, if the number of
items becomes larger, a VME crate may be used.
Under normal accelerator operation we do not yet
use the bunch monitor effectively, mainly because it is hardto predict the beam behavior in the injector section. We
are considering to build operator interfaces to simulation
codes such as PARMELA for buncher sections. A preliminary version was built using Tk toolkits. We hope thatthe combination of beam monitors, such as a bunch monitor and online simulation codes, improve the linac beam
quality for the KEKB upgrade.

Acknowledgment
The authors would like to thank the linac staff forvaluable discussions during the system design. They would
also like to thank the linac operators, especially Mr. S.
Kusano, for their help during the software development ofthe system.

References[1] A. Enomoto et al., “Re-formation of the PF 2.5GeV
Linac to 8 GeV”, these proceedings.
[2] Y. Ogawa et al., “Beam Monitor Utilizing Transition Radiation”, proceedings of the Particle Accelerator Conference, Washington D.C., USA., 1993; KEKPreprint 93–37.
[3] K. Furukawa et al., “Upgrade Plan for the Control System of the KEK e–/e+ Linac”, proceedings of the International Conference on Accelerator
and Large Experimental Physics Control Systems,
Tsukuba, Japan, 1991, pp. 89–92.
N. Kamikubota et al., “New Control System for theKEK Linac”, these proceedings.
[4] K. Furukawa, “Reference Manual for libs2”, not published.
[5] J. Ousterhout, “Tcl and the Tk Toolkit”, AddisonWesley, 1994.