Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

PRESENT STATUS OF THE RCNP CYCLOTRON FACILITY
Accelerator Research Group of RCNP
RCNP, Osaka University, 10-1 Mihogaoka, Ibaraki, 567-0047 Osaka, Japan
Abstract
The Research Center for Nuclear Physics (RCNP)
cyclotron cascade system has been operated to provide
high quality beams for various experiments in nuclear andfundamental physics and applications. In order to increase
the research opportunities, the Azimuthally Varying Field(AVF) cyclotron facility was upgraded recently.
Developments on the flat-topping system and the 18-GHz
superconducting Electron Cyclotron Resonance (ECR)
ion source have been continued to improve the beam’s
quality and intensity. A muon capture beam line (MUSIC)
was constructed in this spring. Developments have been
going on to increase secondary beams like white neutrons,
ultra cold neutrons, muons and unstable nuclei. A
separator is equipped to provide RI beams produced byfusion reactions at low energy and by projectile
fragmentations at intermediate energy. Developments ofmagnets using high temperature superconducting (HTS)
wires have been performed for future applications toaccelerators.

INTRODUCTION
A schematic layout of the RCNP cyclotron facility isshown in Fig. 1. The accelerator cascade consists of aninjector Azimuthally Varying Field (AVF) cyclotron(K=140) and a ring cyclotron (K=400). It provides ultrahigh-quality beams and moderately high-intensity beams
for a wide range of researches in nuclear physics,
fundamental physics, applications, and interdisciplinary
fields. The maximum energy of protons and heavy ionsare 400 and 100 MeV/u, respectively. Sophisticatedexperimental apparatuses are equipped like a pair
spectrometer, a neutron time-of-flight facility with a 100m-long tunnel, a radioactive nuclei separator, a superthermal ultra cold neutron (UCN) source, a white neutron
source, and a RI production system for nuclear chemistry.
A pion capture beam line was installed to provide DCmuons. Such ultra-high-resolution measurements as
ΔE/E=5x10-5 are routinely performed with the GrandRaiden spectrometer by utilizing the dispersion matching
technique. The UCN density was observed to be 19
UCN/cm3 at the experimental port with a beam power of400 W. The white neutron spectrum was calibrated andthe flux was estimated to be 70 % of that obtained at Los
Alamos Neutron Science Center (LANSCE) in the USA.
Neutrons are used for the radiation effect studies on
integrated circuits and so on. Developments of magnets
using high temperature superconducting wires have been
going on for future applications to accelerators. A 3T
dipole magnets is under fabrication.

Figure 1: Layout of the RCNP cyclotron facility.

ACCELERATOR DEVEPOLMENTS
User’s demands on the high beam quality are
expanding rapidly: ultra-high resolution, high intensity, avariety of heavy ions. Since there are no slits orcollimators in the beam lines downstream of the ring
cyclotron, the beam quality on targets is determined by
the characteristics of the injected beam. The AVF upgrade
program for these items is in progress [1-3]. Some ofthem are presented in these proceedings [4,5].

ECR Ion Source
An 18-GHz superconducting ECR ion source wasinstalled in order to increase beam currents and to extend
the variety of ions, especially for highly-charged heavyions, which can be accelerated by RCNP cyclotrons. The
production development of several ion beams and theiracceleration by the AVF cyclotron has been performed
since 2006.
In order to improve the performances of the source, aliner was inserted in the plasma chamber. A bias probe
was installed on the beam axis on the injection side. The
maximum applicable voltage is -500 V relative to theplasma chamber, and the probe position is variable
between 120 and 220 mm from the center of the chamber.

*hatanaka@rcnp.osaka-u.ac.jp-90-Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

The optimum position is located at 170-190 mm, whichcorresponds to the position of the maximum mirror field.
The extraction system is composed of two electrodes andcan be moved along the beam axis. An einzel lens isplaced downstream of the extraction electrodes.
The ion beams extracted from the source are analyzed
by using a dipole magnet and are measured in a Faradaycup placed at the image focal point of the analyzing
system. Detailed performance of the source is presented
somewhere in these proceedings [4]. 8.5 MeV/u 86Kr23+
ions were accelerated by the AVF cyclotron and weredelivered to user’s experiments. In order to produce
metallic boron-ions, a test by using the MIVOC (MetalIon from VOlatile Compounds) method [6] wasperformed using o-carborane (C2B10H12). Its vapour
pressure was around 1-2 Torr at the room temperature.
The o-carborane was put in a glass vessel directly
connected to the plasma chamber via a buffer tank. The
stable flow of the vapour from the o-carborane powder tothe plasma chamber enabled us to produce a fully strippedboron ions. A helium gas was used to generate plasma..

present structure of the Dee electrode, a parasitic
resonance mode is known to exist around 76 MHz. This
resonance is generated in the transversal direction of thedee electrode axis. Beam developments are on-going with
the FT system [5].

2.45 GHz ECR Proton Source

Figure 2: Cross-sectional view of the accelerating systemof the RCNP AVF cyclotron.

Flat-top cavity

Main resonator

1000 mm long and
10 mm wide slot

Main power
amplifierMain power feeder

A proton source is under development to supply highcurrents with a low emittance. It consists of three ringpermanent magnets and no multipole magnets areemployed. Performance tests were finished and 0.6 mA
protons were extracted at 15 kV and with a relatively low
RF power of 200 W. The source has been installed in theinjection beam line. On-line tests will be started this fall.

Dee

Dee voltage
pickup electrode

DEVELOPMENTS OF HTS MAGNETS

Flat-Topping Acceleration SystemA schematic layout of the main and the flat-top
resonators of the AVF cyclotron is shown in Fig. 2. An
additional flat-top cavity of a coaxial movable-short type
is inductively coupled to the main resonator on theopposite side of the main power feeder for fundamentalvoltage production. The flat-top cavity has a length of 700
mm and an outer diameter of 170 mm. A full stroke of theshorting plate of the flat-top cavity is 100 mm. The
coupler electrode and the inner conductor of the flat-top
cavity are shown in Fig. 2. The capacitive coupling
between the electrode and the inner tube of the main
cavity was changed to the inductive coupling from thecapacitive coupling in order to avoid heating problems.
Fine adjustment for 50Ω impedance matching isaccomplished by using a tuner with a full stroke of 40 mm.
A flat-topped dee voltage waveform can be generated
by superimposing a harmonic voltage on the fundamental
one [7]. With the present cavity, the impedance matching
can be achieved over a wide range of harmonicfrequencies from 50 to 80 MHz. Hence, the fifth, seventh,and ninth harmonic modes are available for production of
the flat-topped voltage waveform. Such higher orderharmonic modes have an advantage of saving power forthe harmonic voltage production, because the n-th
harmonic voltage required for flat-toped waveform
production is 1/n2 of the fundamental one [5, 8]. For the-91-

More than two decades have passed since the discoveryof high-temperature superconductor (HTS) materials in1986 [9]. Significant efforts went into the developmentsof new and improved conductor materials [10] and it
became possible to manufacture relatively long HTS
wires of the first generation [11]. Although many
prototype devices using HTS wires have been developed,
these applications are presently rather limited inaccelerator and beam line facilities [12].
Our previous study demonstrated a possibility to excite
HTS magnets with alternating currents (AC) [13,14].
Since HTS systems have higher operating temperatures
than low-temperature superconductor (LTS) systems, thecryogenic components for cooling are simpler and thecooling power of refrigerators is much larger than at 4K.
Because the temperature range for superconductivity iswider than for LTS materials, a larger range of operating
temperatures is available. A high-frequency AC mode
operation should be possible in spite of heating loads dueto AC losses in the coils.
In order to investigate feasibilities of synchrotron
magnets using HTS wire, we are fabricating a super-ferric
dipole magnet to be operated by lumping currents. The
specifications are summarized in Table 1. Upper andlower coils were already fabricated. Each consists of 3
double pancakes of 200 turns. Figure 3 shows double
pancakes for the upper coil. Critical currents of wire weremeasured in full length at 77K. Self-field Ic of wire washigher than 160A. Ic values of double pancakes were 6070A. After stacking, they were 47A and 51A for theupper and lower coil, respectively. There were nodamages in wire during winding process.

Proceedings of the 7th Annual Meeting of Particle Accelerator Society of Japan (August 4-6, 2010, Himeji, Japan)

Table 1: Design parameters of the 3T HTS dipole magnet.
MagnetCoils

Bending radius
Bending angle
Pole gap# of tturns
Winding
Temperature
Rated currentline, low energy heavy ions are delivered to the rareisotope separator and are used to study high spin isomericstates in nuclei.

400mm60deg.
30mm
600 x 23 Double pancakes/coil
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Figure 3: Photograph of double pancakes.

RESEARCH PROGRAMS
Beams are available on targets for 5000-6000 hours ina year. A wide range of research programs are performedat the RCNP cyclotron facility as listed below.
• Few-body problem• Nucleon and nuclear interactions in nuclear medium• Proton/deuteron elastic & inelastic scattering• (p,2p), (p,n), (p,t) reactions• Charge exchange reactions relevant to theastronuclear physics: (4He,6He), (4He,8He)• Giant resonance excited by（p,p’）, (3He,t), (α,α’),(7Li,7Be γ) reactions• Fragmentation of deep hole states in light nuclei• Proton-proton Bremsstrahlung (p,p’γ) reaction• Weak hyperon nucleon interaction by the pn → pΛ
reaction• Heavy ion physics with rare isotopes• Fundamental physics with ultracold neutrons• Applications (neutrons)
Material science
Biological science• Nuclear chemistry
Intensive studies have been performed on the spin andisospin excitation by charge exchange (p,n) and (n,p)
reactions around 300 MeV. The στ nucleon-nucleoninteraction has the maximum strength at this energy
region. The mechanism of these reactions is simple, aswell. We can extract the spin and isospin excitation
strength with least ambiguities. Recent result showed thestrength distribution in the nuclei relevant to 2ν double β
decays [15] of 48Ca.
A beam line was installed to bypass the ring cyclotron
and to directly deliver low-energy, high intensity beams
from the AVF cyclotron to experimental halls. With this-92-