JAERI-Conf 95-021

PB02
Calibration of Beam Position Monitor for the SPring-S Synchrotron
Tsuyoshi Aoki, Hiroto Yonehara, Hiromitsu Suzuki, Norio Tani, Hiroshi AbeKenji Fukami, Soichiro Hayashi, Yasuo Ueyama, Takayoshi Kaneta, Kenji Okanishi
Shigeki Ohzuchi, Takeji Miyaoka*, Kiyokazu Sato*, Eiji Toyoda*, Hiromasa Ito*and Hideaki Yokomizo
JAERI-RIKEN SPring-8 Project Team, Kamigori, Ako-gun, Hyogo, 678-12, Japan*)Toshiba Co, 1-6, Uchisaiwai-cho, 1-chome, Chiyoda-ku, Tokyo, 100, Japan

AbstractBeam position monitors (BPMs) for SPring-8
synchrotron were already designed and manufactured.
80-BPMs were successfully calibrated for the beam
position measurement. In this paper, we introduce thestructure of BPMs, the electronics of signal detection
system and the calibration system, and the results ofcalibration are reported.

position of A and D electrodes are x=24 mm from thecenter of the vacuum chamber to measure the beam
positions on both the reference orbit and the bump orbit
for the beam extraction.
The type 3 pickup has also a 100x30 mm2 vacuum
chamber, and the position of the electrodes are as sameas the type 1. The type 2 and the type 3 pickups arelocated on the straight-section where the beam extraction
systems are placed.

1. Introduction
Beam position monitors, which are placed in the
SPring-8 booster synchrotron, are designed to measure aclosed orbit distortion (COD). The BPMs are located at
the upstream position of SO-quadrupole magnets. EachBPM consists of four button-type electrodes which aremounted on the wall of the vacuum chamber. The
diameter of all the electrodes are 18 mm. Output signals
from the electrodes of 20-BPMs are selected by PINdiode switches, and the amplitudes of these signals aremeasured by the same detection system. Four detection
systems are used at the same time for 80-BPMs, and themeasurement time of this system is less than 30 ms.
The BPMs are calibrated by using an antenna tosimulate an electron beam. The antenna is mounted on
the X-Y table which is driven by the pulse motors. The508.58 MHz signal, which is the acceleration RF in thesynchrotron, is supplied from the tracking generator tothe antenna. The output signals from the electrodes aremeasured by the spectrum analyzer. The normalized
values about horizontal and vertical positions are
obtained by the output signals.
2; Structure of BPM pickup
The BPM pickup consists offour button-type pickup
electrodes which are attached to the SMA-type coaxial
feedthroughs welded on a 80x30 mm2 or 100X30 mm2
racetrack-type vacuum chamber. About the electrode, thediameter is 18 mm and the capacitance with afeedthrough is about 6.8 pF.
We use three types of BPM pickups. The type 1
BPM pickups are placed at 78 positions. The horizontal
distance between the center of the vacuum chamber andthe electrodes is 14 mm. Figure 1 shows a cross-sectionalview of the ~ 1 BPM pickup. The type 2 pickup has a
100x30 mm racetrack-type vacuum chamber, and the80Fig. 1.

The cross-sectional view of a type 1 BPM
pickup3. The Electronics of BPM

The block diagram of BPM electronics for COD
measurement is shown in Fig. 2. The output signals fromthe BPM pickups are transmitted through the 3 dB
attenuators and the coaxial cables to the electrodeselector which consists of fast PIN-diode switches and a600-MHz low-pass filter (LPF). The switching time of
the PIN-diode is less than 0.01 ms, and the duration of
an one-electrode selection is 0.35 ms. The output signals
from the electrode-selectors are transmitted throughlow-loss, high-frequency cables (WF-H50-4) to theBPM-selector.
Heterodyne circuit is used at the detection system.
The 508.58 MHz signal, which frequency is the same
one as the acceleration RF in the synchrotron, istransformed to a signal of 70 MHz intermediate
frequency by mixing with a 438.58 MHz signal from the-251-

JAERI-Conf 95-021

local oscillator. The 70 MHz signal is converted to DClevel as position signal by the synchronous detector andthe 3.5 MHz LPF.
The output signals from the 80-BPM pickups aredetected by four detection circuits. It is expected that thetotal measurement time of 80-BPMs is less than 30 ms.
To measure a single-bunch beam position, the output
signals from a BPM pickup are observed simultaneously
by digital sampling oscilloscope (SONY Tektronix
CSA803A, sampling head SD-26). Five electrodeselectors have functions to change over from COD mode
to single-bunch mode.
4. Calibration System

The schematic diagram of the BPM calibration
system is shown in Fig. 3. To simulate an electron beam,semi-rigid coaxial cable {UT-85) is used for an antenna
and is mounted on the X-Y table which is driven to x, yand s directions by the pulse motors. The coaxial cable isinserted in the stainless steal sleeve which has 3 mm
inside diameter and 5 mm outside diameter. The lengthof the inner conductor out of the sheathe is 50 mm.

The optical sensors are used to set the antenna at theinitial position before every measurement.
The 508.58 MHz signal is amplified and is supplied
to the antenna from the tracking generator output of thespectrum analyzer (HP 8560E). The output signals fromthe electrodes: VA,VB,Vc and Vo are switched byelectrode-selector and are measured by the same
spectrum analyzer. The X-Y table and electrode-selector
are controlled by HP model 362 through the motor
controller and 1/0 box. The offset distances between theinitial position of the antenna and the center of the BPM
pickups have been measured previously, and they arecompensated on the software.
To simulate a distribution of electromagnetic fieldin the beam duct, two dummy ducts are attached bothends of the BPM pickup. To avoid a noise signal by theleaked electromagnetic wave, electromagnetic shieldrubbers are stuck on the inside of dummy duct's outersides and on the base of the antenna. At the longitudinal
position more than 60 mm from the end of sleeve,
electric field distribution is nearly constant. Therefore,
the X-Y table is driven to s-direction that the position
comes on the center of the electrodes.

VME~~~_,----r-----~~~DO. .- 7 - - , ~~~.-~~DO

monitor select signal
data acquisition trigger pulser--O-E~measurement start signal

i... •. _ .• _,,_, _____ ,,_,,_,,_,,_,,_ •• _ .• _ .. _ .. _,,_,,_,,_,,_,,_,,_,,_,,_,,_,,_ •• _ .• _ .• _ .• _ .• _,,~

signal detection system

Fig. 2. The block diagram ofBPM electronics for COD measurement

HPmodel362

antenna

motor'---1===~ controler&I/O box
GPIBspectrum RF out
analyzer sos..ssMHz

Fig. 3. The schematic diagram of BPM calibration system-252-DODI

JAERI-Conf 95-021

5. Result of Calibration

The normalized values calculated with the output
signals from electrodes:
H=(VA-VB-Vc+Vo)/(VA+VB+Vc+Vo) and
V=(VA+VB-Vc-Vo)/(VA+VB+Vc+Vo)are obtained at a position (x,y) of the antenna. Fig.4
shows an example of a result of measurement between(H, V) and (x,y) of type 1 BPM. The calibrated area oftype 1 and type 3 BPM pickup is x=± 15 mm and y=±8mm, and type 2 is from x=-15 mm to x=+25 mm andy=±8mm.

calibration is about 0.1 mm. To estimate the accuracy ofthis calibration system, we calibrated ten times about asame BPM pickup. The deviation of the electric center,
which is the position ofH=V=O, is within 0.04 mm.
6. Conclusion

80-BPMs were successfully calibrated and theaccuracy of calibration was about 0.1 mm. The BPM
pickups are already welded to the beam ducts.

XIJol
TIJol
1.8 ....---::3'9!'........~~-~-,--~-~----,=--~~.8~.6~ f~lllllllllllillllilllllllll~l~.4~.1~ 8.8~ -.1+

$ -.4
II> -.6-.8-1.8 '----~-~~-~-'----~-~~-~-----~-1.8-.6-.8-.4-.1

1.8.8

.6.4

.1

8.8

H=(A·B-C+D)/(A+B+C+D)

An example of a result of measurement
between (H,V) and (x,y) of type 1 BPM

Fig. 4.

The relationship between (x,y) and (H, V) are expressed
as sextic polynomials that obtained by least square
method. Figure 5 shows an example of a calibratedrelationship between (x,y) and (H,V) of type 1 BPM.

8.8
&.4

4.8

3.2'Ee~1.5u>- -1.6-3.2~.8·t4-1.1-15.8~

Fig. 5.

~~~uX [mm]uuuu~An example of a calibrated relationshipbetween (x,y) and (H, V) of type 1 BPM

The precision of the X-Y table is about 0.005 mm
and the accuracy of installation of BPM pickup on thecalibration system is within 0.05 mm. The accuracy ofthe optical sensors to set the antenna at the initial
position is within 0.05 mm. Thus the accuracy of the-253-