Embedded EPICS Controller for KEK Linac Screen Monitor System

THPPC032

M. Satoh, K Mikawa, F. Miyahara, T. Suwada, and K. Furukawa
Accelerator Laboratory, KEK, 1-1 Oho, Tsukuba, Ibaraki 305-0801, JapanT. Kudou and S. Kusano
Mitsubishi Electric System & Service Co., Ltd, 2-8-8 Umezono, Tsukuba, Ibaraki 305-0045, Japan
Abstract

New System

The screen monitor (SC) of the KEK linac is a beamdiagnostics device to measure transverse beam profiles witha fluorescent screen. The screen material is made of 99.5%
Al2O3 and 0.5% CrO3, with which a sufficient amount offluorescent light can be obtained when electron and positron
beams impinge on the screen. By detecting the fluorescentlight with a charge-coupled device (CCD) embedded camera,
the transverse spatial profiles of the beam can be easily
measured. Compact SCs were previously developed in 1995
for the KEKB project. About 110 compact SCs wereinstalled into the beam line at that time. VME-based
computer control system was also developed in order toperform fast and stable control of the SC system. However,the previous system becomes obsolete and hard to maintain.
Recently, a new screen monitor control system for the KEK
electron/positron injector linac has been developed and fully
installed. The new system is an embedded EPICS IOC basedon the Linux/PLC. In this paper, we present the new screen
monitor control system in detail.

System Overview
PLC unit
Klystron gallery
Linac tunnel
Local controller
Air cylinder

Solenid valve
Compressed
air
Driving rod

Beam

Limit switch

ScreenFluorescentlightLED
illumination
Power supply
CCD camera

FIG. 1: Typical screen monitor installedin the beam line at the KEKB injector linac.

Video signalFIG. 2: Block diagram of the screen monitor system.

・Compact SCs were previously developed in 1995 for theKEKB project. About 110 compact SCs were installed into
the beam line at that time as shown in FIGs, 1 and 2 [1, 2].
・The compactness of the monitor along with the fast
control system made it possible to decrease the driving
time of the monitor (~ 0.2 s) from its home position to thecenter of the beam line.
・The screen actuator comprises a driving rod, an air
cylinder driven by compressed air through a solenoid valve.
The screen actuator controls the screen motion into thecenter of the beam line. Fluorescent light emitted from thescreen through a glass viewport is guided down to a floor
level by optical mirrors, and the fluorescent light isdetected by a CCD camera.
・The video signals of the camera are sent to a monitor
control station at the klystron gallery, where a video-signal
selector selects a particular channel corresponding to therequired SC by following an implementation of the control
system. Then, the selected video signal is sent to the main
control room through optical-fiber cables after converting
the electrical signal to an optical signal by an electro-optic
converter (E/O module). The beam-profile image can bemonitored by a TV monitor.

(a)

(b)

FIG. 3: PLC-based screen-monitor control system,(a) front view and (b) rear view.

FIG. 4: Block diagram of the PLC-based screen-monitor
control system.

・Linux-based PLC [3] (FIG. 3)
・The basic functions:a) actuator control (up and down)b) selecting the specified video signal
・When the server receives a control
request from an operator interface(OPI) through the linac control,
it selects a channel of a digital relay
output (DO) module corresponding FIG. 5:Flow chart of the control software in the PLC.
to the specified screen, and then the DO implements the actuatorcontrol (FIG. 4).
・The limit switch signal of the actuator positions is fed into a
digital input (DI) module. The DO module is also used as a videosignal selector in which a video signal outputs from 8 input
channels. The software of the new control system has beendeveloped in EPICS and Linux-based environment [4]. The flow
chart of the control software is shown in FIG. 5.
・EPICS IOC on the PLC selects a specified I/O channel througha device support corresponding to the specified SC according to adatabase.
・OPI has been also developed in Linux environment on the PC.
The main OPI program was developed by using Tcl/Tk scripting
language.

Summary•Toward SuperKEKB project, a new SC monitor control systemusing Linux-based PLC was developed and installed.
• Twelve four controllers in total have been finally replaced inSummer 2011 instead of the old VME-based ones.
•Now, whole the new SC system has been well working without any
fatal troubles, and it is made full use of the linac stable operation.

References[1] T.Suwada, A.Enomoto, T.Urano, and H.Kobayashi, Proceedingsof the 20th Linear Accelerator Meeting in Japan, Osaka, Japan,
1995, pp. 245-247.
[2] T.Suwada, N.Kamikubota, K.Furukawa, and H.Kobayashi,
Proceedings of the 22th Linear Accelerator Meeting in Japan,Sendai, Japan, 1997, pp. 329-331.
[3] http://www.yokogawa.com/.
[4] EPICS home page, http://www.aps.anl.gov/epics/.