JAERI-Conf 95-021

2p1-4
THE NEW EXTERNAL ION SOURCES
AND THE NEW AXIAL INJECTION SYSTEM AT RCNP
M. Sato, K. Hatanaka, K. Hosono, T. Itahashi, T. Saito,
K. Takahisa, H. Tamura, K. Tamura and I. Miura
Research Center for Nuclear Physics, Osaka Univ., 10-1 Mihogaoka, Ibaraki, Osaka 567, Japan

abstract

A new polarized ion source and a new axial injection system have been constructed at RCNP in order
to increase beam intensities and to get high quality
beams. We get a proton current of 50 1-1A in the axial
injection system. The polarization of the proton accelerated by a cyclotron is 70% or more. Beams froman ECR heavy ion source were successfully injected
into AVF cyclotron through the new axial injection
system at the end of September, 1994. We use a spiral inflector instead of the old mirror system to obtain
good transmission of beams.

Variable
Capacitor

Extraction

OrificeElectrostatic Lenses

Figure 1: Schematic layout of the RCNP atomic beam source

1. Introduction

2. The new External Ion Sources

At the Research Center for Nuclear Physics, Osaka
University, a Large fraction of the experimental program is devoted to studies of spin degrees of freedom.
The original atomic beam type polarized ion source
and the axial injection system were constructed in
1975, and since then extensive researches have been
performed with polarized protons and deuterons accelerated by the K140 RCNP AVF cyclotron. In 1991,
a ring cyclotron (K=400) was completed as a post accelerator which is designed to accelerate protons up
to 400 MeV. Polarized proton beam current on thetarget in the scattering chamber was a few nA. In
order to enhance the opportunities in spin physics
research using intermediate energy beams from thering cyclotron, the construction of a new High Intensity Polarized Ion Source (HIPIS) and a new axial
injection system using glaser lenses were proposed asa two years project in 1993. Its design is based on
sources in operation at PSI 1 , TUNV, IUCF 3 , and
RIKEN 4 , which employ cold ( .....,30 K) atomic beamtechnology and electron cyclotron resonance ionizers.
The source is coupled by a high-efficiency bunchingsystem, a high-transmission injection system to the
AVF cyclotron and a spiral inflector system. Bothpolarized ions from HIPIS and unpolarized ions froman ECR source, NEOMAFIOS, are injected throughthe vertical injection system and the inflection system. Due to this injection system we can not only
decrease the maintenance times, but also acceleratehighly charged heavy ions from NEOMAFIOS up to.
higher energies than those from the internal source.

2.1 High Intensity Polarized Ion Source {HIPIS)The overall feature of the HIPIS built at RCNP
is shown in Fig. 1. The beam of H or D atoms is
produced from H 2 or D 2 gas in a 13.6 MHz, ·50.....,200
W discharge contained in a pyrex tube of 20 mm inner diameter. The discharge is cooled by water flowing between the dissociator tube and the second, surrounding pyrex tube of larger diameter, 30 mm. The
Macor serves to isolate the nozzle thermally at .....,30
K from the high temperature of the discharge. The
nozzle is cooled by conduction to the cold head of a
9 W closed cycle helium refrigerator. Helium coolingof the nozzle part of the vessel is very effective to geta high intensity atomic beam. Cooled atoms emerge
as a directed jet from a 3 mm diameter nozzle orifice
into the first vacuum chamber which is evacuated by
a 2800 £/sec turbomolecular pump with a n1agnetic· suspension. With 25 std-cc/min of H 2 flowing into
the dissociator, the pressure in the first chamber is <6.5 X 10- 3 Pa.
An atomic beam is formed at the entrance tothe second vacuum chamber when the beam passes
through a skimmer aperture placed 25 mm from theend of the nozzle. This skimmer separates the firstand second chambers. With other two 2800 1'-fsec turbomolecular pumps on the second chamber, the pressure there is < 1.2 x 10- 4 Pa. A third vacuum chamber follows where another 2800 1'-fsec turbomolecularpump holds the pressure during operation < 3 x 10- 5
Pa.

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JAERI-Conf

95-021The design of the ECR ionizer was essentially basedon that at PSI 1 . The microwave frequency is 2.45
GHz at present. If the magnetic field 87.5 mT deteriorates the proton polarization, we can increase themicrowave frequency higher than 6 GHz.
The desired states of nuclear polarization for Ho
and Do beams are produced bythree sextupole magnets with one weak field radio-frequency transition(RFT) unit between the second and the third magnet, and the second weak field and one (1480 MHz
for H0 ) or two (455 MHz and 331 MHz for Do) strong
field units following the last sextupole. With this configuration, both the pure vector and the pure tensor
states are produced for deuterons.

en

ii

~.

0

~N- ~ :: !t: ~ ECR Source0::l tu 11t=OIQtO"Q'1

r.r~, H~~~~B.EJ"

Dipole Magnet ( H )Db
Mass Analysis
Magnet····--••.
t--····1

Dipole Magnet ( V )Quadrupole Magnet

Steering Magnel
Glaser Lens~~av~~~:lic

2.2 ECR Ion Source (NEOMAFIOS)

Steering Magnet
Glaser lens

NEOMAFIOS is the ECR ion source of 10 GHz RF
frequency for non-polarized light heavy ions. This ion
source has a permanent magnet (Fe-Nd-B) instead ofsolenoidal coil and was built by R. Geller at Grenoble.
Main parameters of NEOMAFIOS is shown in Table
1. Intensities and charge states of typical ions areshown in Table 2.

Beam Buncl1er

Steer~ng Magnet

Glaser lens

Spiral lnfleclor

Figure 2: Injection system of the RCNP AVF cyclotron
Magnetic confinement
RF frequency
Chamber diameter
Chamber length
Evacuating pump

Mirror+ hexapole fieldlOG Hz67mm
170mm
520 !/sec TMPTable 1: Main parameters of NEOMAFIOS

••o

'He

1Lj

"N

1+ 500 1100
2+
580
3+
4+
5+
6+
7+
8+
9+

10
16
2

29
100
145
110 180 96
65 85
6 35 16
2
4

'H

20

Ne ' 0 Ar

cs
34.
50
51
47
35
35
8

Table 2: Intensities and charge states of typical ions

3. Injection System into the AVF Cyclotron
A new injection line for the AVF cyclotron was designed and constructed. In the new system, both polarized ions and unpolarized ions produced with the

NEOMAFIOS are injected through the common vertical injection system and the common inflection system. A schematic layout of the new injection system
is shown in Fig. 2. At the exit of the source, protons
and deuterons are longitudinally polarized. Protons
are deflected by 96.7 degrees with a dipole magnet,
and deuterons by 105 degrees, so that the beam remains longitudinally polarized after the 90 degrees deflection into the vertical beam line. For this purpose,
small parts of pole pieces are added at the magnet entrance when deuterons are injected into the cyclotron.
An electrostatic deflector is used to compensate thebeam trajectory shifts. In the system electrostatic
lenses are used instead of electrostatic ones used in
the previous system. They ensure an efficient focusing and a good vacuum through the line. A beam
buncher is plussed 2.5 m upstream from the medianplane of the cyclotron. It consists of two parallel meshplates forming a single gap, and is excited by an RF
voltage with a sawtooth-like waveform generated by
combining RF sine waves with the first three higher
harmonics.
A spiral inflector system was designed and fabricated. In the previous axial injection system, an electrostatic mirror system 6 has been used to inflect polarized ions on the median plane of the cyclotron. A
spiral inflector seems more suitable for high intensity
beams than a mirror system, because there are no-228-

JAERI-Conf 95-021

grids intersecting beams. A spiral inflector can betreated as a component of a beam transport systemeither analytically or numerically. The shape of electrodes was designed based on the analytic solution of
the Lorentz equation 7 . The electric radius was taken
to be 24 mm, and the magnetic radius of the first
cyclotron orbit 15.1 mm. For 65 MeV protons the injection energy is 15 keV. These parameters were determined by the simulation of a particle orbit in thecentral region of the cyclotron. Numerical integrations of the equation of motion were performed with
an impulse approximati on assuming a Dee voltage 70
kV. The electrode spacing is 6 mm and the electrodewidth is 16 mm. Results of initial testing of the new
system are summarized in Table 1. In the table, theefficiency is the ratio of the beam intensity extracted
from the AVF cyclotron to the beam current measured after the mass analysis magnet in the axial line.
The accelerated beam current increases by a factor 3"' 6 by using the buncher.
4. Developme nt of the Source
4.1 Reliability

During initial off-line testing of the source, it wasnoticed that the ECR ionizer worked stably for periods of more than two months. On the other hand, theatomic beam intensity from the dissociator dropped
by a factor procedure, warming the copper nozzle
to room temperature then cooling it under vacuum,
could not recover the source. The accumulatio n ofgreen spots was observed on the surface of the copper nozzle. The material of the nozzle was changed
from copper to aluminum. In the beginning of theoperation, the aluminum nozzle produced an atomic
beam of similar intensity as the copper nozzle, andthe source could be recovered by a heat cycle. It was
found that the cold nozzle occluded with frozen ammonia. By reducing the N2 gas flow rate to the cold
nozzle, the dissociator now runs stably for periods oflonger than one month before nozzle cleaning is required. With nominal source operating conditions, a
proton current of 50 "' 100 JJA was measured at 15
ke V after the mass analysis magnet in the axial injection line. A maximum proton current of 8 JJA wasextracted from the AVF cyclotron at 65 MeV.

4. 2 Polarization
When the source began to deliver beams for experiments last November, the proton polarization wasmuch lower than expected. The beam line polarimeter measuremen ts indicated an average polarization of
p = 0.55 or less. Extensive investigations have been
performed to optimize source parameters in order toimprove proton polarization . It was found there were
two kinds of sources of unpolarized protons; one wasresidual hydrogen molecules and the other recombined

molecules 1 . The former is now reduced by improved
pumping of the plasma region. The latter was due
to atoms from the dissociator which were not ionizedin the ECR ionizer and recombined on the surface ofquartz vessel containing the plasma or on electrodes.
In the RCNP source, since we use permanent magnet sextupoles to focus the atomic beam, there are
no ways to adjust the hardware of the atomic beamtransport system, so it had to be optimized by simulations using a Monte-Carlo code. Diameters of the nozzle, the skimmer aperture, and the spacing between
them were optimized to improve proton polarization .
The optimum diameter of the nozzle orifice was 3 nun
which is the same as that initially designed. The skimmer aperture diameter was reduced from the initiallydesigned 6 mm to 4 mm. Additional orifices were
installed at weak field RF transition units to reduce
the undesired flow of molecules and atoms to the ionizer. Each orifice has a conductance of 6 fjsec for
air at room temperature . One of two turbomolecu larpumps initially installed at the dissociator was moved
to the exit chamber of the ECR ionizer for improved
pumping of the plasma region. These modifications
improved the average polarization top ,...., 0.75.
Conclusion

The RCNP atomic beam source was successfully
constructed on schedule, and has delivered polarized
proton for nuclear physics experiments at intet'mediate energies. It has operated stably for periods oflonger than one month of continuous operation without maintenance . With normal source operating conditions, a proton current of 50 ,...., 100 JJA was obtained
from the AVF cyclotron at 65 MeV and a polarization
is about 0.75. Future development will be devoted to
improve the degree of polarization , and to get polarized deuterons.
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293, 65 (1994).
[2] T.B. Clegg, AlP Conference Proceedings 187, 1227
(1989).
[3] V. Derenchuk et a!., AlP Conference Proceedings
293, 72 (1994).
[4] H. Okamura et a!., AlP Conference Proceedings
293, 84 (1994).
[5] K. Halbach, Nucl. Instrum. Methods 169,1(1980).
[6] H. Ejiri, RCNP Ann. Rep. (1976) p28.
[7] J. L. Belmont, Institut des Sciences Nucleaires deGrenoble, Rapport Interne ISN 86-106, (1986)-229-