OVERVIEW OF THE RF SYSTEM FOR THE JAERI/KEK HIGHINTENSITY PROTON LINAC
S. Yamaguchi†, S. Anami, S. Fukuda, T. Kato, M. Kawamura, C. Kubota, S. Michizono, H. Nakanishi, M. Ono, KEK,Tsukuba, Ibaraki, 305-0801, Japan
E. Chishiro, K. Suganuma, T. Kobayashi, JAERI, Tokai, Ibaraki, 319-1195, Japan
field stability is ± 1% in amplitude and ± 1degree in phase.

Abstract
The construction of a high-intensity proton linear
accelerator has started as the JAERI/KEK joint project. Theinjector linac provides 400-MeV proton beams for thefollowing 3-GeV rapid-cycling synchrotron. The rf system
for the linac is composed of high-power klystrons, highvoltage DC power supplies, a waveguide system, an rf driveand control system and a buncher, chopper driving system.
An overview of the rf system is presented.

2 RF DRIVE AND CONTROL SYSTEM

324 MHz
klystron

amplifier (10, 30 kW)

LLRF

cavityamplifier (40 W)

HVDCPS

debuncher-2

debuncher-1

ACS-45 ,46

ACS-43, 44

ACS-39, 40

ACS-41, 42

ACS-37, 38

ACS-35, 36

ACS-33, 34

ACS-31, 32

ACS-29, 30

ACS-27, 28

ACS-23, 24

ACS-25, 26

ACS-21, 22

ACS-19, 20

ACS-15, 16972 MHz

Figure 1: Layout of the RF system.
†seiya.yamaguchi@kek.jp

ACS-17, 18

ACS-13, 14

ACS-11, 12

ACS-7, 8

ACS-9, 10

ACS-5, 6buncher-4

buncher-3

SDTL-31, 32

SDTL-29, 30

SDTL-25, 26

SDTL-27, 28

SDTL-23, 24

SDTL-19, 20

SDTL-21, 22

SDTL-17, 18

SDTL-15, 16

SDTL-13, 14

SDTL-11, 12

SDTL-7, 8

SDTL-9, 10

SDTL-5, 6

SDTL-3, 4

DTL-3

SDTL-1, 2

DTL-2

DTL-1buncher-2

buncher-1

chopper

RFQThe construction of a high-intensity proton accelerator
complex has started as a joint project of JAERI and KEK at
the JAERI site in Tokai [1]. This accelerator complex iscomposed of a 400-MeV proton linac, a 3-GeV rapid cycling
synchrotron (RCS) and a 50-GeV synchrotron. The linac
provides proton beams to ADS (Accelerator Driven
Transmutation System) as well as RCS. The role of the rf
source for the linac is to provide rf power to twenty lowenergy accelerating structure modules (an RFQ, 3 DTLs and16 SDTLs) operating at 324 MHz and twenty-three highenergy accelerating structure modules (ACS) operating at972 MHz. The maximum pulse width and the repetition rate
are 650µs and 50 Hz, respectively. The layout of the rf
system is shown in Figure 1. The required accuracy of theACS-3, 41 INTRODUCTION

ACS-1, 2

The drive system [2] distributes a 12-MHz master clock
signal to each station (4 solid state amplifiers and 46klystrons), which will be installed in the klystron gallery
with a total length of 350 m. Accelerating frequencies of324 MHz and 972 MHz are generated at the front end of eachpower station by a voltage-controlled crystal oscillator(VCXO), which is phase-locked with the distributed 12MHz signals. For distributing the 12-MHz signals, phasestabilized optical fibers will be used, which have a phasestability of 1 ppm per °C in order to satisfy the phasestability requirement of ± 1degree for a room-temperaturefluctuation of 2 °C.
In order to stabilize the amplitude and phase of the field in
the accelerating cavity, the feedback and feed-forward control
is used in the low-level rf controller [3]. The feedback andfeed-forward control is performed by a combination ofFPGAs for fast and simple processing and DSPs for slow
and complicated processing. A prototype of the low-level rf
controller is now under testing using an SDTL cavity inhigh-power operation with preliminary results of therequired field stability.

The feasibility of the feedback control of the amplitude
and phase was demonstrated for a DTL test cavity using
analogue modules with two feedback loops: a major loop forthe DTL cavity and a minor loop for the klystron (seeFig.2). Proportional and integral (PI) control using an I/Q
modulator and a demodulator was adopted. The input powerof the cavity was 400 kW.
AMPM
f=324MHz
CW

FB1

BLTB

WR2300

FB2A

amplitude set point
phase set point

DTLK

Minor loop
Major loop

FB1:Feedback Controller 1
FB2;Feedback Controller 2

AMPM:Amplitude & Pulse Modulator

4 WAVEGU IDE S YS TEM

A:RF Amplifier
K:KlystronFigure 2: Block diagram for the test of feedback control.
The measured stability in a pulse was 0.38% rms and0.95% peak in amplitude and 0.24° rms and 0.71° peak inphase. The long-term stability was 0.03% rms (0.18% peak)for the amplitude and 0.24° rms (0.71° peak) for the phase.
The pulse response with electrically simulated “beamloading” was measured using a “beam loading test box” [4].
The test results are shown in Fig 3. Except for the parts forthe rise and fall of the pulse and the start and stop of thebeam loading, almost a flat shape was obtained for both theamplitude and phase. Residual ripples at the start and stop ofbeam loading are to be rejected with the feed- forward
control. The bandwidths of the feedback loop were measured
for the drive amplifier, the klystron and the DTL tank bymeasuring the frequency response for an amplitudemodulated input signal. The measured bandwidths were 53
MHz, 1.2 MHz and 18 kHz, respectively.
20010214_5.kld

(a)

(c)

(b)

(d)

010214_6.kld(b)
15

Amplitude [a.u.]

15

Amplitude [a.u.]

The elements of the waveguide system include circulators(see Fig. 4 (a)), power dividers (b), phase shifters (c),coaxial-waveguidetransformers, E and H corners and dummyloads (d). All of these elements were developed specially forthis project use.

20(a)

10

Beam Loading

510
Beam Loading
5000100

200300400500

600

700

800

0100200300

Time [µs]

400

500

600

700

800

Time [µs]140180010214_5.txt.kld-2

010214_6.txt.kld-2

(c)

175

Phase [deg]

120

110

170165
Beam Loadibg

160
100

Beam Loading

155

90

150
0100

Figure 4: Prototype of the waveguide components: (a)circulator, (b) power divider, (c) phase shifter, and (d)dummy load.

(d)

130

Phase [deg]power. From an experimental investigation and simulation,
it was revealed that the back-streaming electrons scatteredfrom the collector induced these strong oscillations. By
using a large-radiusand long-length collector, theoscillation problem was eliminated.
Gun oscillations were observed for a prototype of a 972MHz klystron [6]. The mechanism is under investigation.
Since one DC power supply drives four klystrons, a largesag (5% in amplitude and 50 degrees in phase) is expected
due to the capacitance of the condenser bank. This sag will
be compensated by feedbackcontrol in a minor loop.

200300400Time [µs]5006007008000100200300400500600700800

Time [µs]Figure 3:Pulse response with electrically simulated beamloading: (a) amplitude without feedback, (b) amplitude withfeedback, (c) phase without feedback, and (d) phase withfeedback.

3 KLYS TRON AN D POWER S U PPLY
As for the 324-MHz klystron [5], an oscillation problem
at the prototype klystron in the development stage wasobserved under high-voltage operation without rf input

The power transmission capability is a 3- MW peak, a 750µs pulse width and a 50-Hz repetition rate (average power is105 kW) for both 324 MHz and 972 MHz. The waveguideused are WR2300 (full size and half-height size) for the 324MHz system and WR975 for the 972 MHz system. In the324-MHz system, where the power from one klystron is fed
to two cavities, it is required the errors of the amplitude andphase at two cavity inputs must be below ±1% and ±1
degree, respectively. The amplitude and phase errors can beadjusted almost independently by tuning a power divider anda phase shifter. Cooling of the waveguide is not necessary
for the 324 MHz system because the temperature rise is
only 1.4°C, even for full power and full duty. On the otherhand, water-cooling is necessary for the 972-MHz systembecause of its high temperature rise (15°C).

5 CHOPPER DRIVING SYSTEM
The chopper driving system is composed of a high-power(30 kW peak) solid-state amplifier and a low-level rf control
system. The time structure generated by the low-level rf
control system is shown in Fig. 5. Specifications of thesolid-state amplifier are shown in Table 1.

amplifiers) for an RFQ, two bunchers and the chopper isalready installed, and that for the DTL1 will soon beconnected to the DTL tank (see Fig.7). We have an RF test
bench in the gallery, which is used for high-power test of
the klystron and waveguide components.

40 ms
500 µs358 ns813 ns(=1/1.23 MHz)

Figure 5: Time structure of the chopper- driving RF.
Table 1: Specifications of the 30 kW solid-state amplifier
for the chopper.
Frequency
324 MHz
Output peak power
30 kW
Rise-fall time
< 20 ns
Phase flatness in a pulse< ±1.5 °Overshoot/undershoot<5%
Pulse-to-pulse fluctuation amplitude < ± 1.5 %phase< ± 1.5 °Harmonics<-60 dB
Circumference temperature
27 ± 2 ° CCoolingforced air cooling

Figure 7: Klystron gallery viewed from the upstream.

7 REFEREN CES

In order to minimize the amount of an incompletely
kicked beam, a very fast rise and fall time (less than 20ns)of the output pulse is required. The measured rise and falltime of the output pulse was 15 ns (see Fig.6).
(a)

0.2

15ns

0.1
0-0.10.10-0.1
-0.2

-0.2
-20(b)

15ns
Amplitude [a.u.]

Amplitude [a.u.]

0.2-10010Time [ns]203040190

200210220230240

250

Time [ns]Figure 6: Pulse shape of the output amplitude: (a) rise time,(b) fall time.

6 RF S OURCE FOR THE 60-MEV LIN AC
The beam commissioning has started for low-energy front
60-MeV proton linac that is being assembled at the KEK
Tsukuba site [7,8]. The rf source (klystrons and solid-state[1] F. Naito, et al.,”The JAERI/KEK Joint Project and its
Performance,” LINAC’02, Kyongju, August 2002.
[2] T. Kobayashi, et al., , “RF Reference Distribution
System for the 400-MeV Proton Linac of the
KEK/JAERI Joint Project,” LINAC’02, Kyongju,
August 2002.
[3] S. Michizono, et al, “Digital RF Control System for
400-MeV Proton Linac of JAERI/KEK Joint Project”,”” LINAC’02, Kyongju, August 2002.
[4] R. J. Pasquinelli and B. Chase, “Linac Low Level RF
Operating Procedure”, Internal memo, Fermi National
Laboratory, (1994).
[5] S. Fukuda, et al.,“ “Performance of 324MHz Klystronfor High Intensity Proton Accelerator Facility,”
LINAC’02, Kyongju, August 2002.
[6] E. Chishiro, T. Kobayashi, M. Yamazaki, H. Suzuki,T. Hori, M. Sakamoto, H. Urakata, S. Miyake, S.
Fukuda, S. Amani, “Development of 972MHz Klystronfor High Intensity Proton Accelerator Facility,”
LINAC’02, Kyongju, August 2002.
[7] A. Ueno, et al.,”Beam Test of a Front-end System for
the JAERI-KEK Joint (JKJ),” LINAC’02, Kyongju,
August 2002.
[8] F. Naito, et al.,”High-Power Test of the SDTL for theJAERI/KEK Joint Project,” LINAC’02, Kyongju,
August 2002.