Proceedings of LINAC 2002, Gyeongju, Korea

HIGH-POWER TEST OF THE SDTL FOR THE JAERI/KEK JOINTPROJECT
F. Naito∗ , Y. Fukui, Z. Igarashi, T. Kato, M. Kawamura, C. Kubota, E. Takasaki, H. Tanaka
S. Yamaguchi and K. Yoshino ,KEK, Tsukuba, Japan
T.Ito, JAERI, Tokai, Japan
Abstract
The separated DTL (SDTL) which accelerates a H− ionbeam from 50 to 190 MeV is one of the main components
in the injection linac for the JAERI/KEK joint project. The
resonant frequency is 324 MHz. It consists of 32 independent tanks. The first two tanks of the SDTL were constructed. The tank cylinders are made with the newly established copper electroforming method on the steel. The highpower conditioning of SDTLs has been completed successfully. The maximum input peak-power was about 500 kW,
which is approximately three times of the required power.
The repetition rate of the rf pulse is 50 Hz and the pulse
length is 600 µsec. The time we spent for the conditioning
for each tank is about 30 hours. The required conditioning
period is extremely short.
Figure 1: Schematic view of the SDTL.

1INTRODUCTION

The construction of a high-intensity proton accelerator
facility, proposed by the Japan Atomic Energy Research Institute (JAERI) and the High Energy Accelerator ResearchOrganization (KEK), has been started at Tokai campus ofJAERI. The accelerator consists of a 400-MeV linac, a 3GeV rapid cycle synchrotron and a 50-GeV synchrotron.
The 400-MeV injection linac is comprised of the a H− ionsource, an RFQ, a drift-tube linac (DTL), a separated DTL(SDTL), an annular-coupled structure (ACS) linac and several beam transport lines.
The separated DTL (SDTL) has been designed as theaccelerator following the Alvarez DTL. The SDTL has nofocussing quadrupole in the drift tube. Instead, the doublet
quadrupole magnet is set between the adjacent tanks of theSDTL. Thus the drift tube has much smaller radius thanthat of the DTL for increasing the shunt impedance [1].
Schematic view of the SDTL is shown in figure 1.
The SDTL consists of 32 independent tanks. The first
two tanks of the SDTL has been constructed and tested bythe high-power rf. The tank assembling data and the resultsof the rf measurement for the SDTL-1 and -2 are describedin the following sections.

length is 1479.4 mm for SDTL-1 and 1531.4 for SDTL-2,respectively. SDTL-32 is the longest tank, which is 2559.3
mm in length. The drift tube is 90 mm in outside diameterand the bore is 30 mm in diameter.
For SDTL-1 and -2, each tube has been aligned on thebeam axis by using an optical alignment telescope within
the error of ± 0.1 mm for x-y plane and ±0.2 mm for zaxis. Measured position for the DTs are shown in figure
2.

2 STRUCTURE
The SDTL tank has five accelerating gaps (5 cells).
Namely the SDTL tank has four full size drift tubes (DTs)in the tank cylinder and two half size DTs on both endplates. The inside diameter of the tank is 520 mm. The tank∗ fujio.naito@kek.jp427

Figure 2: DT position.
The SDTL tank has two fixed tuners and a movable tuner.
The former is used for adjusting the frequency to 324 MHz
and flattening the accelerating field.

Proceedings of LINAC 2002, Gyeongju, Korea
Inside surface of the SDTL tank is formed by the periodic reverse (PR) copper electro-forming method [2],which was already applied to our Alvarez DTL. The basic
properties have been confirmed by the high-power modeltank successfully [3]. The number of the copper layers of
the electroforming for the Alvarez DTL is two.
Standard fabrication process of the electroforming is following:(1) pre-processing on the inner surface of the iron cylinder for the followed electroforming;(2) first PR copper electroforming ( 0.5 mm);(3) lathing the copper surface ( 0.2 mm);(4) 2nd electroforming;(5) lathing;(6) finishing by the electropolishing ( 50 µm), of which
the depth has been chosen in order to get the better surface
condition.
The high performance of the double layered surface has
been already proved by the high-power test of the modeltank of the DTL. However, mono layered electroforming
has been applied to the SDTL 2nd tank (SDTL-2) for decreasing the fabrication cost of the tank, while the SDTL-1
has double layers of the PR copper electroforming for comparison.

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An electric field on the beam axis has been measured by
the bead-pull perturbation method. The field distribution
for SDTL-1 is shown in figure 3. Maximum variation of
the average field in each cell of SDTL-1 is about 1%, which
has been achieved by the adjustment of the fixed tuners.
The calculated shunt impedance for the SDTL-1(Q0 ∼41300) requires the input power of approximately
170 kW for obtaining the 2.5 MV/m field on beam axis.

4 HIGH-POWER CONDITIONING
A high-power conditioning has been done for the SDTL2 at first, which has mono copper layer on the inner surface.
The conditioning of the SDTL-1 has been followed. Theconditioning history for both SDTL-1 and -2 are shown infigures 4 and 5 respectively.

RF PROPERTIESThe unloaded Q-value of the SDTL tank cylinder without the DT has been measured for the TM010 mode. Results
are summarized in table-1. Both the measured Q-values areapproximately 93 % of the calculated one.
Table 1: Q0 of TM010 mode for SDTL tank cylinder.
Tank No.
SDTL-1
SDTL-2

measured (calculated)
65890 (70247)
65740 (70503)

frequency (MHz)440.703440.690

Figure 3: Measured electric field on the beam axis.

Figure 4: Conditioning history for SDTL-1.

Figure 5: Conditioning history for SDTL-2.

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Proceedings of LINAC 2002, Gyeongju, Korea
The conditioning has been started after the tuning of thesystem. The rf conditioning was started with a short pulse( 100 µsec ) and a low repetition rate ( 10 Hz ). The input
peak power was increased gradually up to the design value
for the tank. The rf duty factor then has been extended tothe maximum value of 3% ( 600 µsec in the pulse length,
50 Hz in the repetition rate ). The duty factor was reduced
again when the power level went beyond the design value
and it reached up to 3% at the maximum power level, which
is limited by the radiation safety and for avoiding the riskof the discharge in the tank. The maximum input power
was about 500 kW, which is approximately three times thedesign value and quite high for the conditioning.
The clear evidence, which shows the difference due tothe number of the electroformed copper layers, has notbeen observed for the conditioning of SDTL-1 and -2. We
have decided on the basis of the result that the mono layerof copper electroformed surface is sufficient for the SDTLtank.

5 INPUT COUPLER
RF power is fed into the tank through the input coupler
with ceramic window. Two types of the coupler have beendeveloped for the DTL and SDTL. The designs are shownin the figure of reference [3].
The coupler for the DTL has the ceramic window on thetank wall and a movable loop for changing the coupling to
the tank is located outside of the window. Another one for
SDTL has the coaxial ceramic window and the fixed loop
at the tank wall in vacuum.
Both couplers have been used for the high-power conditioning of the SDTL without any problem. Because themaximum input power ( ∼500 kW, 50 Hz, 600 µsec ) is notenough for the coupler test, the test stand for the coupler,which does not use the SDTL tank, is planned.

6 SCHEDULE
Next 10 SDTL tanks ( No. 3 to 12) will be assembled
at the end of this year at KEK. The conditioning of eachtank will be started immediately after the assembling of thetank. The manufacturing process of the SDTL tanks (No.
13 to 32) has been started. The first one will be completedin 2003.

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REFERENCES[1] T. Kato, KEK Report 92-10 (1992)[2] H. Ino, et al, ”Advanced copper lining for accelerator components”, Proc. of LAC 2000, California, USA, 1015 (2000)[3] F. Naito, et al, ”Development of the 50-MeV DTL for the
JAERI/KEK joint project”, Proc. of LAC 2000, California,USA, 563 (2000)

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