The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

A New System to Control the Cavity Voltage at SOR-RING
Masanori SATOH, Takeyo TSUKAMOTO, Hirofumi KUDO·, Kenji SHINOE·, Hiroyuki TAKAKt,Tadashi KOSEKI·, Norio NAKAMURA. and Yukihide KAMIYA"
Faculty of Science, Science University of Tokyo,
1-3 Kagurazaka Shijuku-ku, Tokyo 162, Japan·synchrotron Radiation Laboratory, The Institute for Solid State Physics (ISSP),The University of Tokyo, Tanashi, Tokyo 188, Japan

Table 1 Main parameters of the RF cavity

Abstract
A new control system for the RF .cavity has beendeveloped and tested at the 500 MeV electron storage ring,
SOR-RING. This upgrade can keep the cavity voltage
almost constant within the range of less than 2 %.

1. Introduction
is an electron storage ring forsynchrotron radiation experiments in the region of vacuum
ultraviolet (VUV) and soft X-ray. It is 17.4 m incircumference and consists of eight bending sections amfour quadrupole triplets. The ring is normally operated at
500 MeV and the stored current is about 200 mA in theroutine operation. The 1.3-GeV Electron Synchrotron (ES),which belongs to the Tanashi Branch Laboratory of theHigh Energy Accelerator Research Organization (KEK), isused as the injector of SOR-RING. Electrons with anenergy of 308 MeV are extracted from ES and injected intoSOR-RING. The injected electrons are accelerated up to 500
MeV in the ring and then stored until the next injection.
The RF frequency of SOR-RING is 120.9 MHz, am
the corresponding harmonic number is seven. The RFcavity of SOR-RING is a re-entrant type cavity with three
RF tuners. Figure 1 shows a schematic view of the cavity
and the tuners. Each RF tuner, called 'flapper', is one-turnshort-circuited loop made of copper. The main parametersof the RF cavity are listed in Table 1.
Two small flappers (No.2 and 3 in Fig. 1) had beenpreviously used to compensate for the beam loading of theRF cavity. The resonant frequency of the cavity is variable
over the range of 500kHz using the two flappers. The loop
angles of the two flappers are controlled by an analog circuit
to keep constant the cavity voltage, which is monitored at apickup loop. The cavity voltage is maintained within therange of 10 % in this system.
A large flapper (flapper No. 1 in Fig. 1) wereinstalled in 1993 to make the frequency adjustment of thecavity quickly. The tuning range of the large flapper isabout 700 kHz. Recently, the control system of the large
flapper has been developed and operated successfully. It is acomputer-controlled system based on the graphicaldevelopment language, HP-VEE. By the new system,
precise control of the cavity. voltage becomes possible.
Thus the cavity voltage can be kept constant within therange of less than 2 %.
SOR-RING[ 11-142-RF frequency
Generator power
Cavity power
Cavity voltage
Accelerating voltage
Shunt impedance
Unloaded Q-value
Loaded Q~value
Coupling coefficient, B
Total tuning range of twosmall flappers
Tuning range of a largeflawer

120.9 MHz
5 kW (typical)
0.5 kW (typical)
22 kV (typical)
4.9 kV (at 500 MeV)
1.1 Mn6400
2900
1.22500kHz
700kHzInput Coupler<D ; Large Flapper@,@ ; Sm~ll Flapper

Fig. 1 SOR-RING RF cavity

The 11th Symposium. on Accelerator Science and Technology, Harima Science.Garden City, 1997

In the following part of this paper, the new system tocontrol the cavity voltage using the large flapper is describedin detail. The relation between the cavity voltage and thebeam lifetime is also presented.

2. The New Cavity Voltage Control system
In the old system using two small flappers, the tuning
angles of the flappers were controlled by an analog circuit.
Since the cavity voltage was controlled only with theaccuracy of 10 %, the behavior of the beam lifetime wasunsteady. In the new system using the large flapper, thetuning angle is controlled precisely by a computer.
Figure 2 shows a schematic view of the control
system. The cavity voltage is monitored by measuring RFpower induced at the pickup loop of RF cavity. Thismeasurement is made by a power meter which is COIUlected
to a computer (Work Station) through the GP-IB bus. Thecontrol system, the program of which has been developedwith HP-VEE (see Fig. 3), compares the measured cavity
voltage and the reference voltage and then generates pulse
signals for the large flapper to compensate for the voltage
difference. A limit switch put on the flapper restricts theangle within 90 degrees which corresponds to 2000 pulses.
There are three operation modes (injection, accelerationand storage modes) in SOR-RING. In the old system, thecavity voltage was changed manually for injection aJXl
acceleration modes.
The new control system runs
automatically for all modes.
~Pulse Signal
unction Gen era tor

IPower Meter~I

RF-Power
1111111

IDigital, . Multimeter. I~

Limit Signal·

Limit Signal Circuit
Pulse Motor
Flapper/.....

IPicku~ Loo~ 1-RF-CAVITY
Fig. 2 Schematic view of the control system.

Fig. 3 HP-VEE-143-

The. 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

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3. Measurements and Results
The stability of the cavity voltage have been measured
in both old and new systems. In the case of the newsystem, the cavity voltage monitored by the pickup loop
was almost constant at a value of 400 [in arbitrary unit] (seeFig. 4), which corresponds to 22 kV. However it wasvaried between 350 to 400 in the old system.
In Figs. 5 and 6, the relation of the cavity voltage andthe beam lifetime is shown. The behavior of the beam
lifetime is apparently improved in the new system.

~~

in ::: ~\\\~~~~·~----~,.~·-~~......~.~··
0>c200;>"'UIIIII

4. Reference[1] H. Kudo et al., "Present Status of SOR-RING", Proc.
the 9th Symposium of Accelerator Science andTechnology, August, 1993, p44.

~00"

3e:~m Lirc!imc

Il500

Timcjhh:mmj

Fig. 4 The cavity voltage.

450

450

ccJOO0):·:200\~\\:.:::(·\.,,~;·i \,\.::::";'~"t··. .,,. ,\......_,______.

I--...----......

I · C:n·ity Volt:1gt I

100,.,~c350::.0?"':i:lO ~c0 t:.·-~--''-------'--~--'--~-......__~----:::' .iOO() L-~--'--~......1.-~-J....._~--'--~--' J()()

OO:IHI

1111:.'0

0 I :00

0 I :JO

02:00

c100:I

02:311

00:00

IIO:JOIll :011

01:.1002:00

112:.111

Timc[hh:mml

Time [hh:mmj

Fig. 5 The beam lifetime and the cavity voltage in the oldsystem.

Fig. 6 The beam lifetime and the cavity voltage in the newsystem.

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