The 9th Symposium on Accelerator Science and Technology, Tsukuba, Japan 1993

Development of the High-Intensity Proton Linac for the lliP
E.Takasaki, S.Anami, S.Fukuda, H.Hanaki, Z.Igarashi, T.Kageyama, T.Kato, M.Kawamura, M.Kihara, T.Kubo, C.Kubota, K.Kudo,Y.Mori, Y.Morozumi, F.Naito, M.Ono, A.Takagi, T.Takenaka, Y.Takeuchi, A.Ueno, K.Yoshino and Y.Yamazaki
National Laboratory for High Energy Physics, KEK
1-1 Oho, Tsukuba-shi, lbaraki-ken, 305, JapanAbstract
For a 1Ge V high-intensity proton linac for the Japanese
Hadron Project (JHP), various accelerator components havebeen developed at KEK; a volume-production type negative ion
source, a long 432MHz RFQ, a drift tube linac (DTL) withpermanent quadrupole magnets and post couplers, an axiallysymmetric annular-coupled structure (ACS) with four slots, anda high-power RF source with 6001.1s pulse-duration. The present
status of these developments is described.
IN1RODUCTION
A lGeV high-intensity proton linac for the JHP was required to inject proton beams to the ring accelerators. The requirements for the JHP linac as an injector are summarized in Table 1.
A working group for the JHP linac was formed in June,
1987. This group proposed that the linac developed should beoperated with extreme stability and reliability and the JHP linac
should be composed of a volume-production type negative ion
source with a low emittance, a 432MHz RFQ linac ( 50ke V to3Me V ), a 432MHz DTL (to 148MeV) with permanent guadrupole
magnets and a 1296MHz high-B linac (to 1GeV ). In Table 2 andFig.l, basic parameters of the JHP linac are given[ I, 2].
In the designing stage, the following was discussed; at first,
radioactivity caused by the beam loss would become the serious
problem in the long-term operation of the Iinac and sometimes
might limit the beam current accelerated. So, sufficiently large
beam acceptances should be secured transversely and longitudinally, respectively. Therefore, the relatively high transition energies of3Me V and 150Me V were chosen for the RFQ to the DTL andfor the DTL to the high··B linac. The frequency of the RFQ and theDTL was chosen to be one-third of the frequency of the high-Blinac.
In order to suppress the beam losses due to the transient effect, it ispreferable to operate the linac with the long beam pulse (400Jls) andthe low repetition rate (50Hz). In order to ensure the large transverse
acceptance, a large bore radius of 1.5cm was chosen for the highS linac. Of course, it is very important for all accelerator components to work with the high stability. So, at first, the high-power RF
station (several MW) with a long pulse length of 600Jls wasconstructed to test the accelerator components with the higher
power level[3, 4, 5, 6, 7].
The technical developments of the linac components havebeen done since 1987. In September, 1993, the RFQ linac will beexcited with the high power and then proton beams will be accelerated up to 3MeV to measure beam characteristics and to compare
the results measured with the designed values. The DTL also will
accelerate the 3MeV beams up to the 5.4MeV after the RF fieldmeasurements.
In the following sections, the present status of the developments is presented.
TABLE 1Requirements for the JHP LinacH"Beam1 GeVEnergy50 Hz
Repetition rate>200 JlA
Average current
2 mnm•mradNormalized emittance (90%)
TABLE2
Basic Parameters of the 1 Ge V Linac
I GeVEnergy500 m
Total length
400 JlS
Beam pulse length
600 JlS
RF pulse length
50 HzRepetition
20 rnA
Peak current
411 m

83.

50 keY
Volu•e-production trpe

148 MeV

3 MeV

Four-vane structurewith ~r-•ode stabilizing loops

High- P 1 1I inao

with the per~anent qu ad rupo e
1agnets and post coup I ers

our-s ot annu ar-coup Ied st rue t ure
with a multi-oavitr bridge coupler
Frequencr; 1296 MHz

Peak bea. current

Frequency; 432 Mllz

Fr equencr; 432 MHz

2011A

RF power ; 0. 8 MW

RF power ; 12 MW(I3 tanks)

RF power ; 99 MW (152 tanks)

Transverse e•ittance(90%)

Transverse acceptance(OO%)

Transverse acceptance(91l'l:)Nor•al ized e1ittanceI ~ru·arad

8.9 ~r••·•rad (bore radius 0.5 mi)

1.1 1rll"llr8d

Acceptable

29 1rmm·11rad (bore radius 1.5 em)
Acceptable

Energy spread(OO%); 0. 03 MeV

Energr spread(90%); I. 4 MeV

Fnergr spread(SO%); 3 MeV

15 deg.

Phase spread(SO%) ; 88 deg.

Phase spread(90%) ; ~ deg.

Phase spread(Sil'l:) ;Figure 1. Structure and parameters of the 1GeV high-intensity proton linac for the JHP-489-I GeVHigh Power RF Sources
The JHP linac requires 36 L-band klystron amplifiers for thehigh-B linac and 14 UHF klystron amplifiers for the RFQ linac andthe DlL. For the extremely stable operation of the proton linac, it
is very important not only to construct the RF source with the highreliability but also to test the accelerator components up to thehigher power level. So, an output RF power of 2 MW for the UHF
and 6 MW for the L-band have been prepared.
At first, a line-type modulator with a peak power of 15MW
(average power of 450kW) had been designed and was constructed
for the L-band klystron (TIIOMSON TH2104A). In this modulator, the main switch used for discharging a 50 stage PFN is the mostimportant device for the highly operational reliability andmaintenability. So, finally, we chose the solid state switch of SCR
as a main switch. In the test and long term operation with the fullpower, we have no problem against this modulator. The L-band
amplifier is composed of a high power pulsed klystron, this modulator, a pulse transformer (step-up ratio of 7) and a low power
circuits. Test of the entire system has been successfully accomplished up to a full power of 5.6 MW with a repetition rate of 50Hz
and a pulse length of 600Jls [8, 9, 10, 11 ]. Now, this L-b~d RFsource has beenusedforthe high powertest oftheACS cavities witha multi-cavity bridge coupler [12] and the RF components .
A high duty UHF (432MHz) RF system consists of twoklystrons (TIIOMSON-CSF, TH21 34), which can produce a 2MW
peak power at the saturation with a nominal duty, two individual
modulating anode controls, a de-power supply (maximum -llOkVwith 46Ax2 beam current) and a low level circuit. The scheme of
the klystron power is shown in Fig.2. At present, the RF system with
only one klystron was accomplished and tested with a nominal duty.
In Fig.3, the result measured at saturation is shown as a function of
the cathode voltage. The UHF RF source sufficiently supplies theRF power of about I MW with about 3% duty into the RFQ linac andthe DlL. In FY 1993, the tank to install another klystron will beconstructed and then the entire system of the UHF RF source will
be completed with a low level circuit, which can be used to control
the amplitude and the phase of the klystron output during the pulse
length and to generate the feedforward signal to compensate thebeam loading [13].

AFigure 2. DC-power supply and modulating anode controls
for the UHF klystrons.
2 ,.,....,-,--,.,.,...,.-·T·~-r-rrr-~1~~~
1 ~ 200(Pdrive=30 W: satwation)
1.8 -oPout(MW)0o.••• ·-·0o,.-o -e'0 ••~,.:-.-:-·...
.o:.··00 ••o.
o-··.. ;,
1.2

. ·•

"......... phase(deg) - -80

II

84

86

88
90
Cathode Vol. (leV)92

Figure 3. Output power and phase shift measured at saturation
as a function of the cathode voltage.
The phase shift per lkV is about 8deg./k:V.

Ion Source
At first, we consider that the cesium vapor, which is essentially utilized in a surface-plasma H- ion source, might cause
easily a break-down in an accelerator using the higher electric field
like the RFQ linac. So, a cesium-free or small consuming H- ionsource is a very useful as an ion source for the JHP. Therefore, thevolume-production type H- ion source was adopted and has beendeveloped at KEK [14, 15].
Recently, by introducing a small amount of the cesium
vapor in the plasma chamber, H- beam intensity was drasticallyincreased. The extracted H- beam current of 20m A was obtained inthis cesium-mode operation. The measured 90% normalized
emittance was about 1 mnm•mrad for 12mA beam and the currentdensity at the anode hole reached to about 70mA/cm 2. It is noted thatthe total drain current which contains mainly electrons from the ion

source is dropped from 350mA to less than 1OOmA. Details of theexplanation of this cesium effects are presented on Ref.16. At
present, in order to accelerate the high intensity H- beam with theRFQ linac, assembling of the ion source is in progress and the power
supplies are prepared.
RFQLinac
The RFQ linac accelerates the H· beams from 50keV to3MeV. So, the length oftheRFQ cavity is about2.7m which is aboutfour times as long as the wavelength [17]. Therefore, in order toavoid the admixture of dipole modes to the accelerating mode,
which reduces the beam acceptance of the RFQ linac, a new fieldstabilization method was proposed by Dr.A.Ueno. The method is-490-

called as a 1t-mo:le statilizing loop (PISL) [18, 19]. In the RFQ
cavity with PISLs, the resonant frequencies of all the dipole modes
were increased much more than that of the accelerating mode as
seen in Fig.4. Details concerning to the PISL are presented on theRef.18. After the studies of the RF property on a cold model(without a vane modulation) with or without PISLs, the RFQ linac
with PISLs was designed and has been constructed as a preinjector
for the JfiP. In this RFQ, it was possible to tune the frequency of theaccelerating mode to the operational frequency of 432MHz and thefield uniformity within ±1% was achieved. So, we could emphasizethat the admixture of dipole modes is drastically suppressed (lessthan 0.5% of the accelerating mode) [20, 21].
At present, the RFQ linac has been installed in the area forthe acceleration test and kept at a high vacuum.
DTL

At first, a cold model (from 3MeV to 8MeV, 35cells, 2.6m
in length with post couplers) made of aluminium was fabricated inorder to obtain the necessary data frr the hot model (3Me V to5.4Me V); for example, an acctlracy of machining and assemblingof the drift tubes and the field stabilization using the post couplers[22]. Next, based upon data measured, the hot model was designed
and has been fabricated. On the other side, the most important
specificationforthepermanentquadrupolemagnets(PQM)required
from the beam dynamics was that the deviation of the field centerfrom the beam axis must be less than 27~lm. So, we chose thefollowing procedures; l) to manufacture the magnet pieces with ahigh accuracy (for magnetization directioo and dimension), 2) toassemlie the PQM in the inner shell of a drift tube and 3) to weld
the inner shell to the outer shell with a stem by the electron beams
seen in Fig. 5. After the electron-beam welding, the difference
between the field center and the mechanical center of the inner shell
has been measured and the results have been within 2011m [23, 24].
Now, the alignment of the drift tubes in the unit tank andconnecting the adjacent unit tanks are in progress.
8.

D(TE11n -A)

A

D(TE11n -B)

Q

Q(TE21n )500 . - - - - - , - - - - - . - - - - ,:r F.

490
N480

.

!:i 470 ················1···············-·r·--------------Eis:: 460 4'5''i':·g:s"M~-.,.------------------r-----------------g. 450 ~-s-~_:_3-~~T----·············--1-·-···············
Q.
1.
440.
.

~High-B Linac
A high-B linac is the standing wave coupled-cell linac(CCL) operated at the 1t/2 mode. As the candidates of the coupledcell cavities, a side-coupled structure (SCS), an alternating-periodic structure (APS) and an annular-coopled structure (ACS) havebeen developed. Considering the problems in the mechanicalstructure and the fabrication process and studying the RF propertyof the various type cold models, we adopted the ACS with the four
coupling slots as a cavity for the CCL.
We have fabricated the several ACS cavities with the fourslots with the different Band the high power test has been carried out
up to 1.5 times of the designed power [25, 26, 27, 28].
REFERENCES[1] M.Kihara, LA-11130-C, p.67; KEK Preprint 86-106.
[2] Y.Yamazaki et al., LA-11432-C, p.80; KEK Preprint 87-159.
[3] M.Kihara, Part. Accel. 32, 1 (1990).
[4] E.Takasaki eta!., KEK Preprint 90-16.
[5] Y.Yamazaki, KEK Preprint 90-15.
[6] Y.Yamazaki and M.Kihara, Proc. 1990 Linear Accel. Conf. p.79 (1990);
KEK Preprint 90-91.
[7] Y.Yamazaki, "Present Status of Development for the JHP 1-GeV ProtonLinac".
[8] M.Ono eta!., Part. Accel. 32, 51 (1990).
[9] S.Anami eta!., Proc. 1990 Linear Accel. Conf. p.l74 (1990).
[10] S.Anami eta!., Nucl. Instr. Meth. A316, 105 (1992).
[11] T.Kubo eta!., Part. Accel. 32, 45 (1990).
[12] Y.Morozumi eta!., Proc. 1990 Linear Accel. Conf. p.153 (1990);
KEK Preprint 90-120.
[13] M.Ono eta!., "432-MHz RF Source For The JHP Proton Linac", submitted
to Proc. 1993 Part. Accel. Conf., Washington.
[14] Y.Mori eta!., Proc. 1990 Linear Accel. Conf. p.680 (1990).
[15] Y.Mori eta!., Proc. 1992 Linear Accel. Conf. p.639 (1992).
[16] T.Okuyama and Y.Mori, Rev. Sci. Instrum.; 63,2711 (1992).
[17] A.Ueno eta!., Proc. 1990 Linear Accel. Conf. p.OO (1990).
[18] A.Ueno and Y.Yamazaki, Nucl. Instr. Meth. A300, 15 (1991).
[19] A.Ueno et al., Proc. 1990 Linear Accel. Conf. p.57 (1990).
[20] A.Ueno and Y.Yamazaki, Proc. 1992 Linear Accel. Conf. p.713 (1992).
[21] A.Ueno and Y.Yamazaki, "Low PowerRF Field Tuning of a four-vane type
RFQ Stabilized with PISLs", this conference.
[22] F. Naito et al., Proc. 1990 Linear Accel. Conf. p.695 (1990).
[23] Y.Iino et al., Proc. 1990 Linear Accel. Conf. p.l23 (1990).
[24] F.Naito et al., Proc. 1992 Linear Accel. Conf. p.320 (1992).
[25] T.Kageyarna et al., Part. Accel. 32, 33 (1990).
[26] T.Kageyama et al., Proc. 1990 Linear Accel. Conf. p.lSO (1990).
[27] K.Yamasu eta!., Proc. 1990 Linear Accel. Conf. p.l26 (1990).
[28] T.Kageyama et al., Proc. 1992 Linear Accel. Conf. p.456 (1992).

Cl)

Cl)
~

:··----------------··············----~--------------------·

1!<4

cj:»33. SSMH~-J.0-,-3-!IMHr------------------r-------,--------

430

01Mode32

NumbernFigure 4. Measured dispersion curves of the TE2ln andthe TElln-A and TElln-B before tuning.
The frequency of the acceleratin g mode was tuned to 432MHz
with the dummy tuners.

Figure 5. The drift tube after the EBW of the inner shellto the outer shell.

-491-