Proceedings of the 20th Linear Accelerator Meeting in Japan ( September 6—8,1995, Osaka Japan)© - 36MECHANICAL DESIGN OF THE NEW SCREEN MONITOR
T. SUW ADA, A. ENOMOTO, T. URANO AND H. KOBAYASHIKEK, National Laboratory for High Energy Physics
1-1 Oho, Tsukuba, Ibaraki, 305 Japan
Abstract

The PF 2.5-GeV linac is now being upgraded for the KEKB project. A new screen monitor has been developed inorder to reinforce the beam monitoring system. The screen monitor comprises a vacuum chamber, an actuator and ascreen. The spatial sizes of all the mechanical components were diminished in order to increase the available space ofthe new beam line. Particularly, the compactness of the actuator made it possible to shorten the driving time of thescreen (-0.2 sec) to the center of the beam line. This report describes the mechanical design of the new screen monitor
in detail.
1 .Introduction

High-current electron beams (6xl010e'/bunch) are
required to produce a sufficient number of positrons for
the KEKB project[l], [2]. The screen monitor isimportant in order to easily handle the beam orbit andto measure the transverse spatial size of such* beams.
About one hundred new screen monitors in total (abouteleven monitors/sector on the average) will be installedin the new beam line. New mechanical design of thescreen monitor could diminish its spatial size,
particularly those of the vacuum chamber and theactuator, and could reduce the price of the monitor.
The compactness of the actuator makes it possible toshorten the driving time and to make the speed of theactuator fast. The price of the monitor is about 2/3
compared with that of the old design due to asimplification of the manufacturing process.

are shown in Table 1 . A double acting-type cylinder,
which has a size of 16 (bore) mm x 5 (stroke) mm, isused so as to be able to push down and pull up thecentral shaft which is connected to the cylinder througha small universal joint. A compressed-air system(-5kgf/cm 2) of the linac can operate the cylinder,
whose operating speed is adjustable by speed
controllers. The cylinder actuates the central shaft
which drives the screen. The central shaft is connected
to an edge of the screen holder joined with a link
(MoS2-coated aluminum) through a coupling pin(SUS304) fixed inside the chamber; it pushes the edge
down and tilts the screen at 450 to the beam line. Asmall bush (phosphor bronze) mounted on the chamber
makes it possible smooth and straight driving of thecentral shaft. The shaft stroke (3mm) is limited by twostopper screws which accurately set the screen center
position to the beam line center.

2. Chamber Design

The new screen chamber was designed so as toincrease the available space (see fig.l). The chamber ismade of stainless steel (SUS 304). The length between
the flange ends was reduced to be 85 mm from 160 mm(old design). The vacuum pipe is 45 mm in diameterand 1.5 mm thick. This vacuum pipe can be directly
joined with a vacuum pipe of a current monitor bywelding. Both ends of the pipe can be connected with aquick-release flange (manufacturer's standard KFflange) which couples by a clamp chain coupling with ametal gasket. This flange makes it possible to easily
mount the screen monitor on the new beam line. Asmall viewport (ICF70) is coupled to the bottom port ofthe chamber. Fluorescent light emitted from the screen
through the viewport is guided down to a support tableof the linac by optical mirrors, and is received by a TVcamera. The actuator is divided from the screen (invacuum) in the chamber by a small bellows.
3. Actuator Design

The screen actuator comprises a central shaft(SUS304), a cylinder (JDA16x5[3]> driven bycompressed air and a micro-solenoid valve (0304E1[3]). A compact commercially available cylinderand vdve were selected so as to be directly mounted onthe chamber. The main specifications of the cylinder

Table 1 Cylinder specifications
Operation
Bore size (mm)Stroke (mm)Operating pressure range (kgf/cm2):ing speed range (mm/s)

Double acting
type165
2.0^7.1
30-500

A micro-solenoid valve using the shading
method[3] is used to control the cylinder driven bycompressed air. The shading method stabilizes thevalve drive. A 200V (AC) power supply controls the“OPEN/CLOSE” of the valve (the load current is〜15mA). The main specifications of the valve are
given in Table 2.
Table 2 Micro-solenoid valve specifications
Operating method
Pressure range (kgf/cm2)
Voltage range (ACV)
Value of current (mA r.m.s)
Insulation resistance (M Q)

Shading method
1.5-7
180〜 250
18 (Inrush)
12 (Holding)>100The driving position of the screen is monitored bya non-contact micro sensor switch (solid state type)
mounted just on the outside of the cylinder. The sensor
switch [3] acts by a small magnet attached to a piston
inside the cylinder. The sensor signal (DC 24V level)
is sent to the linac control system, which monitors theposition status of all the screen monitors. The main
specifications of the sensor switch are given in Table 3.
Table 3 Sensor switch specifications
SI

Applicable stroke (mm)Load voltage (VDC)
Load current (mA)the “OPEN/CLOSE status of the valve. The second(R-2) is used as an auxiliary or for a special screen
monitor (two-step type). Manual control switches arealso available for local tests. A 24V(AC) power line,
which is supplied to a TV camera, is generated byusing a transformer. A 100V(AC) power source is usedfor auxiliary power. The 24V(DC) power which issupplied to illumination lights (LAMP) for the screen isalso generated by using the same transformer and adiode bridge. The position status signals of the cylinderfrom the sensor switch is sent to the linac control
system through this controller.
5. Conclusions

A commercially available screen material(AF995R[4]), which is made of 99.5% A120 3 and 0.5%
C r 0 3, is used to obtain a sufficient amount offluorescent light. The screen size (the size 25x33xllmm3) was reduced in comparison with that (the size50x50x1* mm3) of the old design because of thecompactness of the chamber. This size is large enoughto measure the transverse spatial size of a positron
beam (16 mm in maximum diameter).
44. Local Controller

A local controller will be newly installed. Thiscontroller was mainly designed in an upgrade of thepreinjector of the linac in 1992. A block diagram of theelectric circuit is shown in fig.2. The main powersource (l<j> 3W ，200V(AC)) is supplied to the controller
from the linac power supply system. The power line,
which is controlled using of two electric relays (R-1JI2) through control signals of the linac control system,
is supplied to the valve. The first relay (R-l) controls

A compact screen monitor has been developed
and will be installed in the new beam line. The monitor
length is about half compared with the old type. The
compact screen actuator makes it possible to shorten thedriving time (~0.2sec) to the center of the beam line.
The driving time was reduced to be about 1/3-1/2 incomparison with that of the old type. A quick-releaseflange was used for easy installation into the new beamline.
References[1 ]A Enomoto et al., "REFORMATION OF THE PF
2.5-GEV LINAC TO 8GEV” ，Procs. of the 17th
International Linac Conference, Tsukuba, Japan, Aug.
21-26,1994, pp.184-186.
[2] S, Kurokawa et al., "Accelerator Design of the KEK
も-Factory' B-Factory Accelerator Task Force, KEK
Report 90-24,1991.
[3] KOGANEI Corp., Iidabashi Matsumoto Bldg., 1-21
Agebacho, Shinjyuku, Tokyo.
[4] DEMARQUEST, Z.I. n° 1,27025 EVREUX
Cedex, FRANCE.

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匕びt11^Fig.2. Electric circuit of the local controller.

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