JAERI-Conf 95-021

2p2-1
R&D Status on the High Intensity Proton Accelerator in JAERIK. Hasegawa, M. Mizumoto, J. Kusano, N. Ito, H. Oguri,
Y. Touchi*, H. Ino** and K. Mukugi***
Japan Atomic Energy Research InstituteTokai-mura, Naka-gun, Ibaraki, 319-11

Abstract
The R&D for the high intensity and high duty factor
proton linear accelerator has been carried out since 1991. A
hydrogen ion source, an RFQ and an RF power source havebeen developed and 2 MeV proton beam test has been
conducted to study the front end of the accelerator. To
demonstrate the high duty operation of the DTL, a hot test
model was fabricated and high power test has been carriedout. In this report, present status of the R&D is described.

Introduction
A high intensity proton linear accelerator with an energyof 1.5 GeV and an average current of 10 rnA has been
proposed to perform the various engineering tests for thenuclear waste transmutation system and to apply for the basic
In the R&D for the accelerator
researches[1,2].
accelerator components have beenenergylowdevelopment,developed, since the beam current and the quality are mainly
determined by the low energy portion. Heat removal problemof the accelerator structures is an important issue because of
the high duty factor operation.
To study the front end of the accelerator, the ion source,
the RFQ, and the RF source were fabricated and 2 MeV beam
tests have been performed. In the beam test, acceleration
current of 50 rnA with a duty factor of 6 % was achieved. To
demonstrate the high power and high duty factor operation of
the DTL, a hot test model was fabricated and a high power
test has been carried out by feeding an RF power.

A multicusp type ion source has been developed to obtain ahigh brightness proton beam. The ion source has been
operated successfully at the designed current of 140 rnA at
100 keV[5]. The proton beam from the ion source was
focused by the two solenoids to match to the RFQ acceptance.
The input and the output beam currents of the RFQ weremeasured by the Faraday cups ofFC2 and FC3, respectively,
and the RFQ transmission was deduced. The energy of theproton beam from the RFQ was measured by the compact
magnetic energy analyzer (MEA) installed in the medium
energy beam transport (MEBT). Figure 2 shows the beamenergy spectra for five relative intervane voltages as well as
the P ARMTEQ simulated results. As the vane voltage isreduced, the energy spectrum shifts to the lower energy andmany peaks are observed, which are in good agreement withthe simulated results.
The maximum RFQ output current was 70 rnA at the ion
source extraction current of 155 rnA. The ordinary RFQ
operation current, however, was 50 - 60 rnA at the ion
source current of125- 135 rnA to prevent an overheat to theion source electrodes. The estimated transmission rate throughthe RFQ was around 70 ·%, although the precise proton
fraction in the input beam was not clear due to the mass
separation effects of the solenoids. There are several reasons
to be considered for lower transmission than that of thedesigned value of 95 %. To reveal the reason for the lower
transmission rate, re-alignment of the components, proton
fraction and emittance measurements of the injected beam arebeing prepared.

Beam Test of the 2 MeV RFQ
The RFQ is a four-vane type and designed to accelerate100 rnA (peak) of protons to 2 MeV with a duty factor of 10%[3]. The low power tuning, the high power conditioning
and the first beam test were carried out at the test shop of
Sumitomo Heavy Industries, Ltd. and the basic performanceof the RFQ was obtained[4]. To study further properties, thebeam test has been made at JAERI since November, 1994.
The layout of the RFQ beam test is illustrated in Fig.l.

******Fig.l
Sumitomo Heavy Industries, Ltd.
Mitsubishi Heavy Industries, Ltd.
Mitsubishi Electric Corp.

-233-

Layout of the RFQ beam test
FC: Faraday cup
PM: Beam profile monitor
MEA: Magnetic energy analyzer

JAERI-Conf 95-021

system was examined in the RFQ beam test. Waveforms ofthe forward and reflected power from the RF source to theRFQ, RF pickup level in the tank and accelerated beam areshown in Fig. 3. The amplitude change was remarkably
small to be within 0.5 % when the beam loading was 110
kW. On the other hand, the phase error was relatively large
to be > 5 deg. The feedforward control system will be
examined to improve the phase error.

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Fig. 2 Measured and simulated RFQ beam energy spectra
At the beginning of the beam test in JAERI, the maximum
duty factor was limited less than 2 % due to the partial bum
out of the RF contact at the RFQ. The silver plated spiral type
RF contact, which is made ofbetyllium copper alloy, was used
between the tank and the vane. To improve the heat transfer
properties, it was replaced by a thicker silver plated type. In
addition to the contact replacement, a copper block wasinstalled to cover the open space between the vane and thetank to reduce the heat dissipation at the vane end region. As
a result of these modification, a duty factor of 6 % at thebeam current of 50 mA was achieved. The further study isin progress to achieve the designed duty factor of 10 %.
Development of the 1 MW RF Source

The RF source was designed and manufactured for theRFQ beam test and the D1L high power test. The tetrode tube,
4CM2500KG (ElMAC), is used with three-stage amplifier
configuration[6].
The dummy load tests have been made successfully. TheRF power output of 1 MW was achieved at the duty factor of
0.6 %, whereas the measured gain of the final stage amplifier
is lower than the designed value. The power efficiency was60% which is in good agreement with the designed value of
62 %. At the high duty operation of 12 %, RF power of 830
kW was generated, which satisfied the requirement for thetests in the R&D.
The low level controller of the RF system includes
feedback circuits to compensate power loss and phase shift
due to the beam loading. The performance of the feedback

Fig. 3 RF characteristics of the RFQ operation.
Wavefonns of the forward power to the RFQ (top),reflected power (2-nd), pickup level at the RFQ
tank (3-rd) and accelerated beam (bottom).
High Power Test of the DTL ModelA D1L hot test model with 9 cells, which is a mockup ofthe low energy portion of the DTL, has been fabricated tostudy the RF characteristics and the cooling capabilities[?].
An electromagnetic quadrupole using a hollow conductor(5mmx5mm) was chosen for the focusing magnet, of which
field is 80 T/m with 5.5 turns of 780 amperes. Twoquadrupole magnets have been fabricated and installed in thetest model.
The high power test was carried out with the RF powersource. Figure 4 shows the schematic layout of the test. Prior
to the cooling capability test, high power conditioning was madewith monitoring the vacuum pressure and the RF signals fromthe pickup loop and the directional coupler. In theconditioning, the input RF power of 128 kW with a duty
factor of20 %was fed to the model. Bremsstrahlung X-ray
spectra from the gap were measured to estimate the gapvoltage. The measured gap voltage was 195 kV at the RF
power of 128 kW, which was in good agreement with thecalculated value of 197 kV by the SUPERFISH code.
The measured RF heat dissipation power in the eachdrift tube and end plate was in good agreement with theSUPERFISH results. The frequency shift as a function of the-234-

JAERI-Conf#8 drift tube temperature also agrees well with the calculated
values as shown in Fig. 5. These high power test results
confirm the heat dissipation calculation and the coolingdesign of the DTL.

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95-021establish a reliable operation. These further R&D will be
performed in FY-1995.
To inject the beam into the storage ring for the applicationof the basic researches, negative ion beam is required. The
development of the negative ion source has been started andthe R&D is continued[8].
For construction of the high intensity accelerator
facilities, beam dump is one of the important issues to stop
the accelerated beam effectively and safely. To investigate
a beam stopper fabrication method and its thermal performance,
preliminary mock-up experiment using 2 MeV proton beam
has been started[9].
The superconducting (SC) cavity is one of the feasible
candidates for the high-p structures and its design work is
about to be started. For the injector of the SC cavities,
continuous-beam or much longer duty operation will berequired. Design work on the RFQ and DTL as well as SC
cavities for the CW operation are being performed.

References

ShieldFig. 4 Schematic layout of the DTL high power test

RF Power : 128 [kW)Duty: 20 [%]0'N' -2:;a...<1'-'-4•

Experiments
Calculated-6354045

Temperature ~C)50

Fig .5 Frequency shift of the DTL model tankas a function of the #8 drift tube temperature

Summary and Plan
The R&D with the design and the fabrication of theprototype accelerator structures (ion source, RFQ, DTL andRF source) have been carried out. The good performance ofthe components has been confirmed, while some problems
are remaining. For the RFQ, it is necessary to increase theduty factor and the transmission. For the DTL, erosion andcorrosion in the hollow conductor will be examined to[I] S. Tanaka, "An Outline of Research Facilities of HighIntensity Proton Accelerator", The 1-st Workshop on
Utilization of High Intensity Proton Accelerator, Tokai,
1995, JAERI-Conf95-017, pp.l-8 (1995)[2] M. Mizumoto, "Present Status of High Intensity ProtonAccelerator Development", ibid., pp.9-20 (1995)[3] K. Hasegawa et al., "Design Study on an RFQ for theBasic Technology Accelerator in JAERI",l992 Linear
Accelerator Conference, Ottawa, Canada, AECL-1 0728,pp.314-316 (1992)[4] K. Hasegawa eta/., "First Beam Test of the JAERI 2
MeV RFQ for the BTA", 1994 International LinacConference, Tsukuba, Japan, pp.l13-115 (1994)[5] H. Oguri et al., "A High Brightness Hydrogen Ion Source
for the BTA at JAERI", ibid., pp.381-383[6] Y. Touchi et al., "An RF system for the BTA", Fourth
European Particle Accelerator Conference, London,
1994, pp.l900-1902 (1994)[7] N. Ito et al., "Fabrication and Tests of the DTL Hot
Model in the R&D Works for the Basic Technology
Accelerator (BTA) in JAERI", 1994 International Linac
Conference, Tsukuba, Japan, pp.ll9-121 (1994)[8] H. Oguri et a/., "Development of a High Brightness
Negative Hydrogen Ion Source", these proceedings.
[9] M. Kawai et a/.,"Preliminary Mock-up Experiment of
BTA Beam Stopper with 2 MeV Protons from RFQ atJAERI", The 20th Linear Accelerator Meeting in Japan,Osaka, Japan, pp.320-322 (1995)-235-