Proceedings of the 22nd Linear Accelerator Meeting in Japan

pp-35
N E W S C R E E N M O N IT O R S Y S T E M F O R T H E K E K B IN JE C T O R L IN A C
T. S U W A D A , N. K A M I K U B O T A , K . F U R U K A W A , A N D H. K O B A Y A S H I
K E K , H igh Energy Accelerator Research Organization
1-1 Oho, Tsukuba, Ibaraki, 305 JapanAbstract
The KEKB injector linac is now being upgraded for the KEKB project. A new screen monitor system has beendeveloped in order to reinforce the beam-profile monitoring system. The compact screen monitor was developed inorder to diminish the spatial sizes of all the mechanical components because the available space of the new beam line isrequired to be as large as possible. A new VME-based computer control system was also developed in order to perform
fast and stable control of the monitor system. The compactness of the monitor and fast control system made it possible
to decrease the driving time of the monitor (~0.2 sec) to the center of the beam line. This report describes the hardware
and software design of the new screen monitor system in detail.
1 .Introduction
The KEKB injector linac is required to supply acertain amount of electron beams(8xl09e'/bunch) andpositron beams(4x 109e+/bunch) for the KEKB highenergy and low-energy rings[l]. High-current primaryelectron beams(6x 101°e'/bunch) are also required toproduce such an amount of positron beams. The screen
monitor system is important and essential in order toeasily handle the beam orbits and to measure thetransverse spatial size of such high-current beams.
About one hundred screen monitors in total (elevenmonitors /sector on the average) are being installed in
the new beam line of the linac. A compact screen
monitor was designed and developed in order todiminish the spatial length along to the beam line. A
new VME/OS9-based computer control system wasalso developed in order to reinforce the beammonitoring system which was connected with the linac
control system. The new control system offers fast andstable operation of the beam-monitoring system.
2. System DesignOverview
The screen monitors have been controlled by thelinac control system, which comprises VME front-endcomputers with the OS-9 operating system and UNIXbased workstations[2,3]. In 1993, the number ofscreen monitors was typically 2-5 per each sector. As apart of the KEKB project, we decided to improve ourbeam-monitor system:a) increase the number of screen monitors,b) introduce new beam-monitors (beam-position
monitors and wire scanners), andc) digitize the waveforms of wall-current monitors.
Since the existing front-end computers do not havesufficient CPU power for these new requirements, newfront-end computers were introduced for exclusive use.
The new ones are essentially the same as those of thelinac control system; however, the main CPU ha been
upgraded from MC68040(25 MHz) to MC68060 (50MHz). A more detailed discussion has been given
elsewhere[4].
A new network system was also introduced inconjunction with the KEKB project. As shown in

Figure 1，all of the front-end computers are linked to aswitching-hub with a star-topology. Fiber-optic cables
are used for physical connections in order to avoid
electromagnetic noise from high-power klystrons. The
hub has a link to the linac control network, whereUNIX workstations and man-machine interfaces areconnected.
All of the screen monitors are controlled byeighteen front-end computers and a few UNIX
workstations. Each front-end computer is located on
the linac klystron gallery (an upper floor over the linac
tunnel) at a nearly equal interval along the beam line,
and takes care of the above-mentioned monitor systems
for a half sector. Six screen monitors on the average
are controlled by each front-end for a half sector of thebeam line.
Mechanical design
Figure 2 shows a picture of the new screenmonitor. The monitor is made of stainless-steel
chamber (SUS 304)，an actuator, and a screen material.
The length between the flange ends was reduced to be
85 mm from 160 mm (old design). The vacuum pipe
can be directly joined with a beam pipe of a current
monitor by welding, which is insulated by a ceramic
insulator. A quick-release flange (manufacturer’sstandard KF flange) is used which couples by a clamp
chain coupling with a metal gasket in order to make itpossible to easily mount the monitor on the beam line.
A small viewport (ICF70) is coupled to the bottom portof the chamber to extract fluorescent light emitted fromthe screen. The actuator comprises a central shaft，acompact cylinder with a size of 16 (bore) mm x 5(stroke) mm, driven by a compressed-air system(5kgf/cm2) in the linac and a micro-solenoid valve. A
compact commercially available actuator was selectedso as to be directly mounted on the chamber. The
driving speed of the actuator is adjustable by speedcontrol tuners which control the amount of compressed
inlet and outlet air. The central shaft stroke is 3mm,limited by two stopper screws which accurately set thescreen center position to the center of the beam line.
The driving position of the screen is monitored by anon-contact micro sensor switch (solid state type)
mounted just on the cylinder. The sensor signals aresent to the monitor control system, which monitors theposition status of all the screen monitors. Details
concerning the mechanical design has been reported
elsewhere[5].

Fig. 2 Photograph of the new screen monitor.
Beam profile monitoring

A commercially available screen material(AF995R[6]), which is made of 99.5% Al20 3 and 0.5%
C r 0 3, is used to obtain a sufficient amount offluorescent light. The screen size (25x33xll mm3) wasreduced in comparison with that of the old design(50x50x11mm3) because of the compactness of thechamber. This size is large enough to measure thetransverse spatial size of even a positron beam.
A block diagram of the screen monitor system isshown in Fig.3. Fluorescent light emitted from thescreen through the viewport is guided down to asupport table of the linac by optical mirrors, and isreceived by a standard CCD camera. The video signals
are sent to a monitor control station, in which therequired signal is selected by a video-signal selector.
Then, the selected video signals are sent to the main
control room through optical-fiber cables afterconverting them to optical signals by electrooptic
converters (E/O modules). The beam-profile images
can be monitored by TV monitors in the main controlroom.
Local controller

A local controller set for each screen monitor in
the linac tunnel is mainly used to test the monitor driveby manual switches and to tune the speed of theactuator at the time of linac commissioning. Thecontroller also supplys power sources for the actuator(AC 200V), screen illumination light (DC 24V) and a
CCD camera (AC 24V). The limit switch signals, whichshow the actuator’s position status, are sent to monitor
selector modules through this controller.
Control software

The server program for the screen monitors arealways running at UNIX workstations during linac
operation. The basic functions provided by the serverare: a) actuator control (up and down), and b) selecting
the specified video signal.
When a server receives a control request, itsearches for the fron-end computer where the specified
screen is installed, then asks for “some work” to thefront-end computer. The communication between
UNIX workstations and front-end computers is madeover the linac control network using the TCP/IP
protocol[4,7]. As shown in Fig.3, the font-end
computer has digital in/out modules[8]. Actuators arecontrolled by a digital output module. The limit switch
signals of the actuator positions are fed into a digital
input module. The digital output module is also usedfor controlling video-signal selectors, which output avideo signal from eight input signals. At the end of“the work’’， the fron-end informs the server that thework has been completed.
Since we utilize the software of the present
control system, no additional developments for thebasic control software were needed in the present
upgrade. However, the device drivers (digital in/out)
were modified in order to use them with the new CPU
chip (MC68060).
Man-machine interface

Two man-machine interfaces are available at themain control room. One is touch-sensitive terminals
based on the NEC PC (80x86, DOS-based)[9]. Thissystem was developed as a part of the present control
system, and has been operational since 1992. Anotheris a new Windows-NT application, which wasdeveloped in recent years[10]. The application supports
mouse-oriented operation without keyboards. Visual
Basic has been used as a development language so as torealize easier maintenace and better visualization. Bothinterfaces send control requests to a server according tothe operator’s requests.
3. Summary

A compact screen monitor system has beendeveloped, and is being installed in the new beam line
for the KEKB injector linac. The monitor length along
to the beam axis is about half compared with the oldtype. The compact screen actuator makes it possible toshorten the driving time (〜0.2sec) to the center of thebeam line. A new VME-based control system and manmachine interface were also developed in order toperform fast and stable operation for the beammonitoring system.
References[1]S. Kurokawa et al., KEK Report 90-24, 1991.
[2] N. Kamikubota, et al” Procs. Int’l Conf. on Acc.
and Large Exp. Phys. Cont. Systems

(ICALEPCS’95)，Chicago, Oct. 1995, FERMILAB
Conf-96/069 p. 1052.
[3] N. Kamikubota, et al” Procs. of the 20th LinearAcc. Meeting in Japan, Osaka, Japan, 1995, p.209.
[4] I. Sato, et al., KEK Report 95-18(1996).
[5] T. Suwada, et al., Procs. of the 20th Linear Acc.
Meeting in Japan, Osaka, Japan, 1995, p.245.
[6] DEMARQUEST, Z.I. n° 1,27025 EVREUX
Cedex, FRANCE.
WindowsNT
PCs[7] N. Kamikubota, et al., KEK-Intemal 95-22 (1996).
[8] Profort PVME501, 80-bit digital in/out module.
INTERNIX Inc., Shinjyuku Hamada Bldg.，7-4-7
Nishishinjyuku, Shinjyukuku, Tokyo.
[9] N. Kamikubota, et al., Procs. ofthe 17th LinearAcc. Meeting in Japan, Sendai, Japan, 1992, p.276.
[10] I. Abe, et al., Procs. ofthe 17th Linear Acc.
Meeting in Japan, Osaka, Japan, 1995, p.224. .

Touch-sensitive
terminals
Switching-Hub(for front-end computers)
fiber-optic cables
to other front-end computers

Front-endcomputer(VME)

Front-endcomputer(VME)

Front-endcomputer(VME)

Fig.l Block diagram of the monitor network system
Monitor Control Station

Beam monitor network
to Linac control network(TCP/IP protocol)
i ,•,^ Optical-fiber cableto Main control room ^ ，ふ , • ---- -----(Video signal)

Network Repeater
E/O Modules
Video-Signal Selector
Monitor Selector
33P 0U I U Joo30
3{npos0 9 0 9Ddu

Consoleterminal
Klystron gallery
L inac tunnel

Local controller
Actuator
Air cylinder
Driving rode"/e+ beam
Flizn

AC power &Limit switch
signals
Screen;cent light 令Illumination

JI
CCD camera

AC power

Fig. 3 Block diagram of the screen monitor system.

Video signal