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

Introduction of Solid State RF Sources at the KEK 40-MeV Proton Linac
Zenei IGARASHI, Kesao NANMO, Tatem TAKENAKA and Eiichi TAKASAKIKEK: High Energy Accelerator Research Organization
1-1, Oho, Tsukuba, Ibaraki, 305 JAPAN2 The solid state rf power amplifier

Abstract
At the KEK 40-MeV proton linac, solid state rfpower
amplifi~rs were introduced into rf sources for the two tanks ofthe DTL and for the prebuncher; furthermore, introduction tothe debuncher's rf source is now in progress. These rf sources
have been operated stably without any problem.
In this paper, the solid state rf sources and their operational
results are described.

1 Introduction
Since construction of the KEK proton linac, four
amplifier chains comprising many amplifiers using vacuum
tubes (Fig. I) had been used as rf sources for the prebuncher,the two tanks of the DTL and the debuncher. However, theserf sources have caused problems due to the short-lived vacumm
tubes or discharges of the high-voltage power supplies. In thelatter half of 1980's, due to requests of easy maintenance, safty
and reliability, an all soid state rf power amplifier generating
several tens of kW in the VHF or UHF band for the rador
system or TV transmitter were developed[ 1]. In thatcircumstance, we at first decided to use the solid state rf power
amplifier as a predriver of the rf source for the 2nd tank.

The solid state rf power amplifier generally consists ofsome modules which contain several tens of rf powertransistors, which generate several kW. Thus, for pulse
operation we refined the module that was originally designed
for cw operation of a TV transmitter by NEC corporation[2].
Figs.2 and 3 show the refined module and its blockdiagram.
Fig .4 shows the output versus the input characteristics of themodule. The rf power transistor used in the final stage of themodule is the 2SC3286-M, adopting the so-called Gemini
package, in which two transistor chips are mounted for pushpull operation, and generating about 200W. The maximum
ratings and electrical characteristics of the transistor are givenin Table.l.

-Table.1 Characteristics of 2SC3286-M
Maximum ratings
veBO = 55V, veEO = 32V, VEBO = 3V
Ie = 24A, PT = 280W
Electrical characteristics
P0 = 140W typ@ f=230MHz, Vee =28V, P,N =lOW
P0 = 200W typ@ f=230MHz, Vee =37V, P1N = 14Wr; e = 65% typ
DEilUNCHER

BEAM

replace by the solid state

amplifiersFig.1 Block diagram of the rf sources for the KEK 40-MeV proton linac-182-

Fig.2 Module (type P2KCH)

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

MC5388ATT

RF-IN~t-UMMTTERSHIFTER

Fig.5

The predriverFig.3 Block diagram of the module
2.2 Rf source for the prebuncher

P2KCH TR-PA(NEC)The rf source shown in Fig.6 contains three modules&nd a stripline 3-way combiner[3].

.
.
·············~,',,,:···············j.····· ······~.~ .................;...... 91 82.7644"""

2000

I I

S.N0=114· · · · ..r···· ···r··-·l· ·:~:r:::·T ·[ 1500
1-::>

a.

· · · · · · · ·······r·········r···;:~:~:~~,,

1-5 1000
500·r··············-r····..······r······vc2=37V

0~---+----~--~--~----+----r02

345Fig.7 Stripline 3-waycombiner

6INPUT(mW)

Fig.6 Rf source for theprebuncher

Fig.4 Output versus input characteristics of the module

CAPTURE EFFICIENCY(%) versus P.B FIELD

2.1 Predrivers of the if sources for the two tanks of the DTL

The predriver of the rf sources for the 2nd tank of theDTL, that contained the six modules and generated about
15kW, was introduced into the rf system instead of the 7651
amplifier, as can be seen in Fig. I in 1988[2]. Fig.5 shows
this predriver. To combine the outputs of the six modules,
three coaxial2-way combiners and a stripline 3-way combiner
are used. This rf source has the function to increase its output
power to compensate the beam loading receiving the trigger
pulse. Since the solid state amplifier with an output power ofabout 15kW had operated very well, therefore, we introduced
the same one into the rf source for the 1st tank in 1990.
Scince introducing the predrivers, we have experienced
four problems which occured in the DC24V power supply,
the blower for cooling, the trigger circuits, and the display
pannel for displaying the output power, the AC voltage andthe DC voltage. However we have never experienced any
trouble in the module, itself.

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80 PJT.r~1T.Dn~nn~naT.r~+r.pq;-60><uz.r.l
HuH""r.l""..:

M :I+5040--9-7. 3(kW)-+-7.0(kW)--6.0(kW)-B-5.0(kW)-----4. O(kW)........ 3.0(kW)........ 2.0(kW)-+-l.O(kW)-+-O.O(kW)3020-200204060

PHASE(deg)Fig.8 Beam capture efficiency
versus the prebuncher field

0 140

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

The stripline forms the quarter-wave-length impedance
transformer. Fig.7 shows this combiner.
Because this rf source stably generates 7kW larger thanthat of the old one, as shown in Fig.l, the beam-capture
efficiency of the linac increase from about 60% to 74%[4].
Fig.8 shows the capture efficiency versus the prebuncher
fields.
2 .3The rf source for the debuncher

Containing the nine modules, this rf source, which joinsthree rf sources with just the same method as that for theprebuncher, generates about 20kW[5]. Three stripline 3-way
combiners, which are the same as that for the prebuncher,and a coaxial (WX-39D) 3-way combiner (Flg.9) are used.
Fig.IO and Fig.ll show the otutput, the phase versus the input
characteristics and an output waveform of20kW, respectively.
The rf source is shown in Fig.12 after installation.
Fig.12 Rf source for the debuncher

3 Co111clusion
Introducing the solid state rf source has
decreased the problems during operation, improved thesafety and reliability and facilitated maintenance. It isthus proved that an solid state rf source of several tens
kW at VHF band works well for the proton lihac.
Fig.9Toaxial 3-way combiner

RefeJrence

20kW ALL SOLID STATE AMPLIFIER FOR D.B[l]Z.Igarashi et al.," ALL SOLID STATE RF
POWER AMPLIFIER FOR PROTON LINAC"
Proc. 6th Symp. Ace. Sci. and Tech., 1987, p86.
[2]Z.Igarashi et al., "lOKW ALL SOLID STATE RF
POWER AMPLIFIER",
Proc. 13th Linac meeting, 1988, p34.
[3]Z.Igarashi et al., "RENEWAL OF TilE RF

4030"~m~105---·

20.

··········0l

SOURCE FOR THE PREBUNCHER AT KEK

PROTON LINAC.",
Proc. 21th Linac meeting, 1996, p195.
[4]E.Takasaki et al., "Effects of Controlling the40Me V Proton Linac on Transversal Motions "Proceedings of this meeting.
[5]Z.Igarashi et al., "RENEWAL OF TilE RF
SOURCE FOR THE DEBUNCHER AT KEK
PROTON LINAC ",Proc. 22th Linac meeting, 1997,.

100681012CONTROL VOLTAGE (V)

Fig.l 0 Output, phase versus input characteristics
TekJLIii Trig'dM Pos: 160.0,m:-•••-•-MOOHOM-•-•-•-•-••-:•:-:-·:-:·:·:-·:::-:-:-••••-•-:••••••--••:-••••-•oo-•--•••-·:..:.:_:..:.:.:.:..-------·~---~~-:!

~~.;....,--...,.-'_:_:

U"""""""' 1:112 UJUva.l

M lW.IJStXt J (Fig.ll Output waveform of 20kW

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