. T.he 11th Symposium on Accelerator Science and Technology, Harima Science GardenCity, 1997

Development of High Intensity Accelerator
For Neutron Science Project
OGURI.
Motoharu MIZUMOTO. Joichi KUSANO. Kazuo HASEGAWA. Nobuo OUCID. Hidetomo
INO.
HiroshiI.
Michikazu KINSHO. Yutaka TOUCill . Yoichiro HONDA. Ken MUKUG
RFumirua NOD A. Nobuo AKAOKA. Hiroshi KANEKO. Etsuji Chishiro. Benjamin FECHNE
Proton Accelerator Laboratory
Japan Atomic Energy Research InstituteTokai-mura. Naka-gun. lbaraki-ken 319-1 L Japan

Abstract
The high-intensity proton linear accelerator with anenergy of 1.5GeV and an average current of 5.33mA has
been proposed for the Neutron Science Project (NSP) at
JAERI. The NSP is aiming at exploring nuclear
technologies for nuclear waste transmutation and various
basic research fields such as condensed matter physics
based on a proton induced spallation neutrons. The R&D
work has been carried out for the components of the frontend of the proton accelerator. For the high energy portion
above lOOMeV. superconducting (SC) linac has been
designed and developed as a major option. A high intensity
proton storage ring is also studied for basic research facility.
1.

Introduction

After the partitioning and transmutation research
program for high level radioactive nuclear wastes, OMEGA.
was proposed by the Japan Atomic Energy Agency (AEC)
in 1988. JAERI started an intensive work to study theaccelerator-driven transmutation system of minor actinides.
The JAERI's activities cover the development of an highintensity proton accelerator development. In recent years.
there has been an additional growing interest in new intense

neutron sources for basic research fileds. While previous
neutron source development has been mainly concentrated
in neutron data measurements for· fission reactor
development. new sources · are largely required for
applications in material sciences. In material sciences. alarge nmnber of investigations involve slow neutron
scattering techniques. and many of these have been carriedout at high-flux fission reactors. An alternative teclmology.
however. started to attract the strong interest for generating
neutrons based on the intense proton accelerator.
In addition to such basic neutron researches. manypotential applications for applying the intense accelerator
has been discussed. which include spallation RI beam
(mainly for nuclear physics studies). meson/muon
production and radio isotope production. A conceptual
layout of the accelerator for the Neutron Science Project isshown in Fig. 1[1].
JAERI had originally planned to build the pulsed linac
with an energy of 1.5GeV and a peak current of lOOmA
with 10% duty factor. The design study has been intended
to obtain the technical validity to accelerate high peakcurrent '"ith high duty operation from the beam dynamics
point of view. In this accelerator development. the R&D
work has been continued on high brightness ion source.
radio frequency quadrupole linac (RFQ). drift tube linac

Nuclear Transmutation.Enegineering Facility

Uti I ity Service Bui ldiqg
llation RI-Beam Faci I ity0Neutron Physics
Nuclear Transmutation Physics

Fig. 1 Conceptual Layout for Neutron Science Project-130-500m

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

achieved. was 70mA at the ion source extraction current of155mA with 10% duty factor. The transmission in the low
energy beam transport (LEBT) fonn ion source to RFQ wasabout 60% witl1 the proton fraction of 80% in the ion source
beam. The estimated transmission rate through the RFQ
was 80%.

(DTL) and RF source. as well as the conceptual design of
the whole accelerator components. In the beam test. thecurrent of 70mA with a duty factor of 10% has been
accelerated from the RFQ at the energy of2MeV[2].
JAERI has modified the original plan by proposing an
option of superconducting (SC) linac to meet requirements
for a variety of basic researches mentioned above and an
ultimate goal for waste transmutation. This SC linac will be
operated in pulse as a first stage for the spallation neutron
source and gradually upgraded toward CW by increasing
duty factor. The SC linacs have several favorable
characteristics as follows: the length of the linac can bereduced. which can meet the requirement from the limitedarea of the site and high duty operation can be made forsimultaneous experiments. The possibility to inexpensive
operation cost may be found in comparison with nonnal
conducting (NC) option.
Preliminary specifications for the NSP LINAC aregiven in Table 1. Neutron scattering facility will require
strict pulse time structure. The beam chopping capability
with about 1j..LS intennediate pulse length will be needed tocompress the beam width by the storage ring.

2.

Low Energy Accelerator Part

Beam tests of the 2Me T· R&D-RFQ
In the case of a high intensity accelerator, it isparticularly important to maintain the good beam quality(low emittance: small beam size and divergence) andminimize beam losses to avoid damage and activation of theaccelerator structures. The R&D work for the low energy
portion has been made as a first step in the NSP-LINAC
development. The R&D-RFQ is a four-vane type anddesigned to accelerate lOOmA (peak) of protons to 2MeV
\Vith a duty factor of lO%. The low power tuning, the highpower conditioning and the first beam test were carried out.
The proton beam from the 1OOke V ion source was focusedby the two solenoids to match the RFQ acceptance. Themaximum RFQ output current. which was currently
2.1

2.2. Low energy part.for the NSP-linac
As the first R&D stage of the ion source development. apositive hydrogen source was fabricated and successfully
operated at the full design values of 1OOke V and 140mA
peak. The negative ion beam is then required for basic
science researches to inject the beam into t11e storage ringwhich produces specific pulse widtl1 and repetition rate. The
beam extractor of the existing positive ion source used for ·previous beam e:\:periment was modified to produce
negative ion beams from source ion plasma by providing thetransverse magnetic field. The characteristics of thenegative ion beam have been examined with the 1naximum
observed beam current of 5.5mA at an arc discharge power
ofl8kW.
Because the superconducting accelerator has been
selected for the high ~ linac. the low energy part should becapable for the CW mode operation. The design study has
been started to develop the CW-RFQ cavity in the range of-30mA. Since the most important problem for the R&DRFQ was found to be the RF contact between vane and tank.
the CW-RFQ as integrated type· by brazing between vaneand tank in under investigation.
The parameters for the CW-DTL are also re-evaluatedto match the CW operation for the new superconducting
design concept. Accelerator gradient is selected 1. 5MeV/min order to reduce the RF power consumption and the RFheating. The e:-q>ected maximum magnetic field gradientfor the focusing magnet is about 60T/m using the hollow
conductor type Q-magnet. The end point energy for theDTL is lOOMe V which is determined from the beam
dynamics and mechanical consideration of t11e high ~structure. The 1/3 scale Aluminum cold model for an

Table 1 Preliminary specifications of the JAERI NSP Linac
Parameters

Operational conditions

Energy:Accelerated particle :Average current: First stag:l.5GeV
Negative and positive hydrogen ionlmA
Maximum 5. 33mA
Nonnal-conducting linac: 200MHz
Super-conducting linac: 600:MHz
Pulse mode operation
CW/pulse mode operation
maximum 50Hz
2ms (atlmA operation) ->maximum CW
400ns (interYal 270ns)
nominal 30mA
60%:

Low energy part Second stage:
High energy part
Pulse structure First stage :Second stage:
Repetition rate
Macropulse width
Intennediate pulse width
Chopping factor: Peak current-131-

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

injection part of DTL up to lOMe V has been fabricated toevaluate conditions of the post couplers. Some basic
parameters for the accelerating field stabilization has beenobtained[3].

3.

High Energy Accelerator Part

3.1. La_vout of the superconducting linac
Superconducting cavity is selected as a main candidate
for high energy portion. In the proton accelerators. theproton velocities ~ gradually change from 0.43 to 0.92
corresponding to the energies for lOOMeV and 1.5GeV.
Accordingly. the length of the cavity also has to be changed.
Main concern is the strength of the cavity under the vacuum
load for the low~ (~<0.7) region. The mechanical structure
calculations with the ABAQUS code have been made todetermine the cavity shape parameters as well as
electromagnetic ones with the SUPERFISH code.
In order to determine the layout of the SC acceleratingstructure. a typical case of the SC linac. which is composedof 8 different ~ sections has been studied. The cavities ineach ~ section will be made identical with 5 cells anddesigned at the specific beam energy but also can beoperated at slightly different beam energy with lower
efficiency.
3.2. Test ofsupercond ucting cavities
The test stand for a superconducting cavity
development with the cryostat 80cm dia. x 350cm long anda clean room has been constructed [4]. A single SC test
cavity has been fabricated for f:3 =0.5 which corresponds tothe proton energy of 145MeV. Fabrication process such as
cold rolling and press of pure Niobium metallic sheet
electron beam welding, surface treatment (barrel polishing.
electro-polishing and high pressure water rinsing. etc.) has
been perfonned based on the KEK experiences for 500.MHzTRISTAN Cjlvity. A first vertical test has been conducted to
examine the RF and mechanical properties. The maximum
field strength of 20MV/m for 4.2K and 26.6MV/m for 2.1K
have been successfully obtained as first time for proton SCaccelerator. This test result has satisfied the specification
for the conceptual layout of the superconducting linac.

4 Proton Storage Ring
In the beam storage ring, the pulsed beam from thelinac is accumulated. and high imensity pulsed beam is
produced for the neutron scattering experiment. The linac
beam is chopped to 670ns bunch width with 60% duty cycle
at 50Hz. The 1.5GeV R linac beam is compressed bymeans of a multi-turn charge exchange injection. When aharmonic number of the ring is l. a circumference and arevolution frequency are 185m and 1.49MHz. respectively.
The single bunch in the ring is contained by RF resonantcavity. To achieve a beam power of 5MW with this beamstructure. it is necessary to accumulate 4.17xl0 14 protons. It
is important to examine reduction and localization of thebeam loss with sufficient considerations of the divergence ofthe beam by the space charge force. the resonancephenomena by the tune shift and longitudinal instability.
The design studies and beam simulation for such highintensity proton ring have been carried out and somepreliminary results have been obtained [5.6]5.

Summary

The R&D work for the prototype linac stmctures hasbeen performed. The good performance of the components
has been achieved. Since 1995. the basic specification for
the accelerator has been changed such as negative ionacceleration. SC cavity option and storage ring. The new
design modification has been started. The test stand for theSC cavities has been constructed. The design work on theRFQ and DTL as well as SC cavities for the CW operation
is being perfonned. The vertical cavity test has beensuccessfully conducted resulting in the satisfactory
maximum electric field strength for SC proton linac.

Acknowledgement
The authors would like to thank Drs. S.Noguchi. K.Saitoand E.Kako of KEK and S.Takeuci of JAERI for
discussions and help on the SC cavity development. They
also thank Drs. T.Kato. I. Yamane and Y.Yamazaki ofKEK.
R.A.Jameson of LANL and Y.Suzuki of JAERI for valuablesuggestions about the beam dynamics calculations andaccelerator system optimization.

References[1] M. Mizumoto et al. "'A High Intensity Proton Linac
Development for Neutron Science Research Program··
XVIII International Linac Conference. LINAC96.
Geneva. Switzerland 26-30 August 1996. p662-664[2] K. Hasegawa et aL ""The Development of a HighIntensity RFQ at JAERI'". J. Nucl. Sci. Techno!..
Vol.34, No.7. (1997) p622-627[3] E. Chishiro et aL ·'A Cold Model Test of the CW-DTL
for the Neutron Science Project at JAERI"". In theseproceedings.
[4] J. Kusano et aL "Superconducting Single Cell Cavity
Test for Neutron Science Project at JAEru··. In theseproceedings.
[5] M. Kinsho et al.. '·A Preliminary Study of the Proton
Storage Ring for the Neutron Science Project at
J AERI'". In these proceedings.
[6] F. Noda et al.. ·'A Beam Simulation of the Proton
Storage Ring for the Neutron Science Project"". In theseproceedings-132-