LOW-POWER RF SYSTEMS FOR THE KEKB INJECTOR LINAC
H. Hanaki, S. Anami, S. Fukuda, H. Katagiri, T. Matsumoto & S. Michizono
High Energy Accelerator Research Organization, KEK
1-1 Oho, Tsukuba, Ibaraki, 305-, Japangenerate 60-kW RF pulses and to modulate theiramplitude and phase for operating a SLED. Two new ones
were installed for the extended part of the linac.

Abstract
The low-power rf systems of the KEK electron linac havebeen upgraded for the KEKB. The main drive system isequipped with a new frequency multiplier/divider whichgenerates five reference signals for the linac and the KEKBring. The multiplier/divider was manufactured so as tohave a very low noise performance in order to minimize
any rf phase jitter. Eight sub-boosters, which drive fouror eight high-power klystrons, respectively, werereinforced to generate 60-kW rf pulses. A solid-state 10kW amplifier was newly installed for the 571-MHz subharmonic buncher. New RF sources are equipped with
new PLC-based controllers which having panel displays.
1

Reinforcement of the RF Sources of the Electron Linac
2.5-GeV Linac8-GeV Linac
High Power RF Sources
Klystron
30-MW type40/50-MW type(48 units)(58 units)
Modulator
pulse output 80 MW
108 MW
SLED056
Energy gain
65 MeV/unit
160 MeV/unit

INTRODUCTION

The KEK electron linac, which will be an injector for theKEKB collider rings, will have its energy upgraded from
2.5 to 8 GeV by increasing both the RF power and thetotal accelerator length[1].
The reinforcement of the RF sources is summarized inthe following table. Increasing the acceleration RF poweris mainly performed by replacing klystrons and adopting aSLED. The klystron modulators had been upgraded[2] inorder to increase the output power and to extend the highvoltage pulse width up to 4 µs on its flat top. The 30MW Klystrons had been replaced by a new 50-MW
type[3]. A SLED, which is an RF-pulse compressor, hadbeen installed in every high-power RF source[4], asshown in Figure 1, except for two, which require severe
phase and amplitude control. Sub-booster amplifiers,
which drive high-power klystrons, were reinforced so as toCW571 MHz

Schematic Diagramof the RF SystemMAIN DRIVESYSTEM

Low Power RF Sources
6 units
8 units
10-kW type × 260-kW typevacuum-tube type solid-state typevacuum-tube type solid-state type
119 MHz 5 kW
114 MHz 20 kW
476 MHz 5 kW
571 MHz 10 kW

Sub-booster
Klystron
Modulator
SHB amplifier

2

MAIN DRIVE SYSTEM

In the case of the previous TRISTAN main ring, the RFfrequency for acceleration was not completely
synchronized with beam injection from the linac.
However, the KEKB project requires their synchronization
within 30 ps. Therefore, the frequency for the KEKB ring
RF system had to be shifted in range from 508.3 MHz to508.9 MHz in order to have complete synchronization
with the linac RF for acceleration. Finally, we fixed thefollowing RF frequencies:
2856 MHz

Ref. Signal
Generator

E/O

Optical Lines
SUB-BOOSTER 2
O/E

114 MHz571 MHz
DriverTrigger
System60kW
Klystron
SUB DRIVE LINE

Coaxial Lines

SB-A

SB-B

SB-C

IΦA

SB-1

1 kW
Amp.
System

SB-3

SB-4

SB-5

50MW
Klystron

1 kW
Amp.
SystemSLED

Solid-State
Amp.
20 kW
e114
MHzElectronGun

SHB1

10 kW

Target571MHzPrebuncher
SHB2
Buncher

Sector A

Sector B

Sector C Sector 1e+ e-ACC

Sector 2

Figure 1 Diagram of the upgraded RF system

Sector 3 Sector 4 Sector 5

The RF frequencies for the KEKB
Fundamental
10.38546 MHzKEKB ring RF
508.88754 MHz
Linac SHB1
114.24006 MHz
Linac SHB2571.2003 MHz
Linac acceleration
2856.0015 MHz
The specification of the injection-beam-energy
distribution requires low phase jitter of less than 1 degree(or 1 ps). The master frequency of the linac RF system
must be chosen so as to minimize the phase noise ofreference signals. Consequently, the frequency for subharmonic buncher (SHB) 2 was determined to be themaster frequency, and the synthesizer HP 8662A wasemployed for the master oscillator.
MAIN DRIVE SYSTEM
Five Reference Signal Generator
571.2 MHzfor SHB2 Amplifier

114.2 MHzMaster
Oscillator
571.2 MHzCounter
1/55

Phase
Detector

114.2 MHzfor SHB1 Amplifier

VCXO

RF powers are 20 kW for 114 MHz and 10 kW for 571
MHz.
The previous 119-MHz SHB amplifier (5 kW) had
been reinforced before making a new amplifier. Twovacuum-tube type amplifier units (for final stage) weretuned and cascaded so as to generate 15-kW RF pulses atmaximum. A new 20-kW solid-state type will replace thepresent one in 2000.
A 571-MHz solid-state amplifier was newly
manufactured and installed last spring. This amplifiersystem, as illustrated in Figure 3, comprises ten amplifier
modules, a preamplifier, an amplitude & phase controller
and a phase stabilizer. The amplifier, itself, made byNEC, is manufactured by modifying a cw amplifier forbroadcast use.
The sources of phase variations of the microwaves
stored in the SHB cavity are the amplifier, thetransmission line, or the cavity, itself. The phasestabilizer compensates for these phase variations.
Specification of the 571-MHz amplifierTypesolid-state, AB classFrequency
571.2 ±5 MHz
Output power
10 kW
Input power
1 mW
Pulse width
10 - 50 µs
Pulse repetition
50 ppsLong-term variation
Amplitude±1.5 % (AGC off)Phase
±1.5 deg.

Counter
1/11

10.385 MHz

10.385 MHz
for Ring Trigger
508.9 MHz

Phase
Detector

508.9 MHzfor Ring RF

VCXOCounter
1/49
Counter
1/2×11

SAMPLERIF 57.1 MHzCounter
1/102856 MHz
for Sub-Boosters

Phase
Detector

2856 MHzYTOE/OOptical Linesfor SB-2,3,4,5
Coaxial Linesfor SB-A,B,C,1

Figure 2 Block diagram of the main drive system
A reference signal source divides and multiplies themaster frequency to generate the above-mentioned fivefrequencies. The signal generator, which was designed andmanufactured by Sony/Tektronix, satisfies thespecifications by means of precision PLL circuits
represented in Figure 2.
The reference 2856 MHz has been fed to sectors 2,3,4
and 5 by optical cables so as to minimize any phase shift
in the long transmission line caused by room-temperaturevariations. For the extended part of the linac, coaxial
cables transmit reference signals to sectors A,B,C and 1,
because we gave priority to eliminating phase drifts with
E/O or O/E converters.
This main drive system, except for the master
oscillator, is mounted in a thermostatic chamber, which
regulates the inside temperature at 28±0.2 ˚C. Thus, any
slow phase drift is minimized.
3SHB AMPLIFIER SYSTEM

The primary electron beam for positron production is
specified to be a single bunch of 10 nC at the target.
That is, the sub-harmonic bunchers must strongly
compress the high-current electron beam in order toprevent the production of satellite bunches. The requiredDivider

571 MHz SHBAMPLIFIER SYSTEM

1 kW

Combiner

10 kW
LinearAmplifier

Gate
Pulse
IΦA
571.2 MHzReference

DividerΦΦSHB
CavityCombiner

AM

10 kW
MonitorFeedback
Controller
Local/RemoteController
S/H
DBM

Phase
Stabilizer

Figure 3 571-MHz solid-state amplifier system
4

SUB-BOOSTER SYSTEM

In order to operate the SLED's we upgraded the subbooster system as follows (Figure 4): (1) Amplitude
modulators and 0-π phase modulators were installed inevery sub-booster. Thus, the sub-booster can generate
rectangular RF pulses with a 4-µs width and can reverse
their phases of the last 1 µs for SLED operation. (2) The
phase modulator has a voltage-controlled fast phase shifter
in it; the rise time of its control voltage is variable from67 to 400 ns. A slow phase-reverse time, such as 300 ns,

reduces the power level of RF pulses reflected by theaccelerator guide. (3) Every sub-booster station wasrelocated from the center of the sector to its head. Thus,since the timing of the accelerating RF pulses can beoptimized, the beam energy can subsequently bemaximized. (4) A 60-kW klystron, which can drive eight
50-MW klystrons, was newly developed. New pulse
power supplies were also manufactured for the klystron.
It is equipped with a solid-state switch (36 kV, 16A)
instead of a vacuum tube for higher reliability.
A feedback controller was installed in every klystrondrive circuit in order to stabilize the phase and amplitudeof the cw-RF signal amplified by a 3-W amplifier. Thisstabilized signal is transmitted to every RF monitor
station[5] as a phase reference. The drive circuits aremounted in thermostatic chambers as well as the maindrive system.
An RF-phase drift of the sub-booster strongly depends
on the temperature of the cooling water for the klystron.
The observed phase-temperature coefficient is about 1deg/˚C.
Specification of the sub-booster
KlystronFrequency
2856 MHz
Output power
60 kW
Cathode voltage-25 kV
Pulse width
4 µs
Pulse repetition
50 ppsLong-term variation
Amplitude±0.3 %
Phase±1 deg.

supported. We thus had to prepare a new device controller
with high reliability and with good maintainability.
The design policy of the new controller is as follows:(1) high reliability of the hardware and network
communication against severe EMI, (2) easy maintenanceof the hard/software, (3) direct replacement with an oldtype controller. Consequently, we developed a PLC-basedcontroller. It has a TFT display with a touch panel for auser interface and optical Ethernet ports forcommunication.
The following fundamental functions of the newcontroller are the same as that of the old one:
• remote ON/OFF operation• finding an interlock signal changed first• remote operation of an RF devices, such as a phaseshifter• communication with a device manager
The controller also supports the following newfunctions:• GUI for easy understanding and for easy local operation• local trend displays of monitored signals, such as theRF powers or the pressures in the wave guides• statistical processes of analog data
• automatic conditioning of an RF unit
The new controllers were introduced in the extended
part of the linac and have worked without any problem forthe last half year.
RF DEVICE CONTROL SYSTEM
Ion Pump
Power Suplly

Pressure
Data

VacuumController

UNIXDevice Manager

VXI
RF Monitor
SystemRFSignals

Data Flow

Simplified Network

SUB-BOOSTER AMPLIFIER
OpticalReference
2856 MHz

Klystron Modulator

THERMOSTATIC CHAMBER
28 ± 0.2 °C
Phase &CW 3 W
Amplitude
O/E
Stabilizer

For a Reference line

Local
Controller

Peak PowerMeter
Timing
Pulse

IΦA

Φ0AM

0.5 W

ConsolePC GUI

TFT
Display

Modulator
Devices
For High Power
Klystrons

PM

PLC
Assembly

RS/Loop3
Converter

60 kW
KlystronπRemote Controller

ON/OFFInterlock
DC Signals

SLED Detuner
Controller

IP

De-QingTriggerIΦA

0

Figure 5 Block diagram of RF-device control-25 kV

Remote I/O Unit

OpticalEthernet

OpticalCable

Solid-StatePulse Modulator

Ion Pump
Power Supply

30 kV DCPower Supply

Focus Magnet
Power Supply

Local/Remote Controller

Figure 4 Sub-booster amplifier system
5RF-DEVICE CONTROLLER

The RF-device controllers for the klystron modulator haveworked for over 15 years. However, some of them arestarting to show a remarkable failure rate ofcommunication. It is easily expected that most of thefailure will be caused by severe electromagnetic noise
emitted by the reinforced modulators. In addition, it will
be difficult to maintain the network for the controller overthe next ten years, because it is not commercially

6REFERENCES[1] A. Enomoto, et al., "Reformation of the PF 2.5 GeV
Linac to 8 GeV", Proceedings of the 1994 Inter-nationalLinac Conference (Tsukuba), p 184.
[2] H. Honma, et al., "Upgrade of the PF 2.5-GeV Linac
Klystron Modulator for the KEK B-Factory Project",
Proceedings of the 1994 International Linac Conference(Tsukuba), p 436.
[3] S. Fukuda, et al., "Development of the B-Factory Linac
50-MW pulsed klystron", Proceedings of the 1994
International Linac Conference (Tsukuba),p 427.
[4] H. Hanaki, et al., "Use of SLEDs for High-GradientAcceleration", Proceedings of the 1994 International
Linac Conference (Tsukuba), p 430.
[5] H. Katagiri, et al., "Microwave monitor systems for
KEKB injector linac", in this proceedings.