SPIRAL at GANIL: Latest Results and Plans for the Future

Abstract

The first accelerated exotic beam of the SPIRAL (Production System of Radioactive Ion and Acceleration On-Line) facility at GANIL at Caen has been delivered for experiments in September 2001. After working for almost 5 years, 32 experiments were performed in the facility using exotic isotopes of helium, oxygen, neon, argon and krypton. The intensities of the radioactive beams increased since the first beam was delivered. Nominal intensity values are achieved for most of noble gas beams. Developments of new beams as well as the increasing of present intensities for a number of isotopes are being undertaken. In particular, in this contribution it is presented the first results obtained for the production of light alkali beams. Other developments are also envisaged in the close future.

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SPIRAL at GANIL: Latest Results and Plans for the Future
A.C.C. Villaria, C. Eleona, R. Alves-Cond´ ea, J.C. Angeliqueb, C. Baru´ ea, C. Caneta,
M. Duboisa, M. Dupuisa, J.L. Flambarda, G. Gauberta, P. Jardina, N. Lecesnea,
P. Leherissiera, F. Lemagnena, R. Leroya, L. Maunouryc, J.Y. Pacqueta, F. Pellemoinea,
M.G. Saint-Laurenta, C. Stodela, and J.C. Thomasa
aGANIL (IN2P3/CNRS - DSM/CEA) B.P. 55027 14076 Caen Cedex 5, France
bLPC - ENSICAEN , 6 bd. Mar´ echal Juin 14050 Caen Cedex, France
cCIRIL - ENSICAEN , 6 bd. Mar´ echal Juin 14050 Caen Cedex, France
The first accelerated exotic beam of the SPIRAL (Production System of Radioactive Ion
and Acceleration On-Line) facility at GANIL at Caen has been delivered for experiments
in September 2001. After working for almost 5 years, 32 experiments were performed
in the facility using exotic isotopes of helium, oxygen, neon, argon and krypton. The
intensities of the radioactive beams increased since the first beam was delivered. Nominal
intensity values are achieved for most of noble gas beams. Developments of new beams
as well as the increasing of present intensities for a number of isotopes are being un-
dertaken. In particular, in this contribution it is presented the first results obtained for
the production of light alkali beams. Other developments are also envisaged in the close
future.
1. INTRODUCTION
The use of high-energy fragmentation as well as the ISOL (Isotopic Separation On-
Line) methods for exploring the structure of nuclei far from stability became one of the
major activities at GANIL (Grand Acc´ el´ erateur National dIons Lourds), the first opera-
tional high intensity heavy ion accelerator in the 50-100 MeV/nucleon domain. It turns
out from the principle of production and separation using a spectrograph, the so-called
in-flight method [1], that the optimum efficiency of the process is reached when the ra-
dioactive beam has a velocity similar to that of the primary beam. This production
process, however, does imply losses in intensity and/or quality of the secondary beam,
which becomes increasingly important as the beam is slowed down. The ISOL (Isotopic
Separation On-Line) method, used at SPIRAL [2], provides for production and separa-
tion of radioactive ion beams, with subsequent acceleration by a K=265 cyclotron (CIME,
Cyclotron d’ Ions ` a Moyenne Energie) between 1.7 and 25A MeV. This opened up the
possibility to study nuclear reactions around and slightly above the Coulomb barrier with
radioactive ion beams at GANIL. In brief, the general scheme of the SPIRAL project is
the following: the series of the three GANIL cyclotrons is used as a driver which bombards
a production target placed in a heavily shielded cave located beneath ground level in the

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2A.C.C. Villari, C. Eleon, R. Alves-Cond´ e et al.
accelerator building (Figure 1).
Figure 1. GANIL and SPIRAL acceleration system. C01 and C02 are the injector cy-
clotrons. CSS1 and CSS2 are the separated sector cyclotrons. TIS is the target ion source
production system of SPIRAL. CIME is the radioactive beam cyclotron. Radioactive ion
beams (RIB) are delivered after selection by the alpha-shaped spectrometer.
In addition to the target-ion source system, both high and low-energy ”front-ends”
are installed in the cave. The exotic nuclei produced by nuclear reactions are released
from the high temperature target (2000oC), then pass through a cold transfer tube into
an ECRIS source where they are ionized up to a charge-to-mass ratio larger than 1/11.
After extraction from the ECRIS with an acceleration voltage up to 36 kV, the low-energy
beam is selected by a relatively low-resolution separator (m/∆m = 250) and injected into
CIME. The exotic beams can be accelerated in an energy range of 1.7A MeV to 25A
MeV and, after extraction, the proper magnetic rigidity is selected by the modified alpha
spectrometer of GANIL and directed to one of the existing experimental caves. The mass
separation is performed for the most part by the cyclotron itself with a resolving power
of more than 2,500. An additional separation can be achieved by stripping at the object
point of the spectrometer in order to select ions having the same charge-to-mass ratio but
different masses, or by using a degrader to select the isobars. However, an intensity loss
is the price to be paid for either of these two methods.
2. TARGET-ION SOURCE PRODUCTION SYSTEM
In the classic ISOL technique a proton or a light-ion beam is accelerated to a high
energy and bombards a thick target, producing radioactive nuclei by spallation reactions,
fragmentation of the target and/or induced fission. Other reaction mechanisms, however,
come into play with heavy ions. In particular, projectile fragmentation is the process
of most importance.In all cases, the fragments are stopped in the target, which is
heated to a high temperature to facilitate the migration of the radioactive atoms to the
surface. Usually the target is located at a short distance from the ion source and the

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SPIRAL at GANIL: Latest Results and Plans for the Future3
radioactive atoms effuse via a transfer tube to the plasma region where they are ionized
and then accelerated. As the atoms are ionized and accelerated in a manner identical to
that for stable beams, the resulting radioactive beams have good dynamical and optical
characteristics when compared with projectile fragmentation, as well as an energy, which
may be precisely adjusted. The originality of the GANIL project lies in the use of an
extended range of heavy ions, up to the maximum available energies. Such an approach
differs from the proton (or light-ion) beam technique in that the projectile rather than
the target is varied in order to produce the different radioactive species, thereby allowing
the use of the most resilient and efficient production target for most cases. For SPIRAL,
the high-energy beam delivered by the present GANIL cyclotrons interacts with a thick
target, where all the reaction products are stopped. The target is thereby heated by
the primary beam up to 2000oC. Such a temperature is a challenge for the target in
terms of reliability and duration. A numerical code has been developed to simulate the
temperature distribution inside the target and is described in [3]. It can be shown with
this code that convenient temperatures (about 2000oC) can be achieved with high primary
beam powers if the target presents a conical shape. In the case of a low power primary
beam, extra ohmic heating can be added through the axis of the target to maintain the
diffusion of the exotic ion beam.
Figure 2.
right one is specially designed for production
of He isotopes (see text). The pictures corre-
spond to targets for maximum beam power
of 1,500W.
SPIRAL graphite targets. The Figure 3. SPIRAL target ion source en-
semble. The ECRIS NANOGAN-3 as well
as the target container are mounted in a
support plate, which can be remotely re-
moved from the production cave.
After production and diffusion, the radioactive atoms effuse to the ion source through
a cold transfer tube that makes a chemical selection, as the main part of the non-gaseous
elements sticks on the walls of the tube. The atoms then enter into the ECR (Electron
Cyclotron Resonance) ion source Nanogan-3 [4] where they are ionized and extracted

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4A.C.C. Villari, C. Eleon, R. Alves-Cond´ e et al.
to form the radioactive ion beam. The number of radioactive atoms created by this
method depends on the primary beam intensity, which has been recently upgraded [5],
and on the integrated fragmentation cross section. However the creation rate of nuclei
of interest is always low, and the major problem of the method is to be as efficient
as possible in order to maintain suitable radioactive ion beam intensity. This means
that the system of production of the radioactive ion beam has to take into account all
the loss processes that can occur, like sticking on the walls, leaks, chemical reactions,
etc. The production time, including diffusion out of the target, effusion, ionisation and
confinement, has to be compatible with the life-time of the nuclei of interest. In order
to test the properties of the target ion source (TIS) systems, the separator SIRa (limited
to 400W of primary beam power) was built in 1993. It allowed the test of different
configurations of production systems under real conditions [6],[7],[8],[9].
Nanogan-3 configuration is composed of a graphite target (Figure 2) with a microstructure
with 1µm grain size, coupled to a 10 GHz permanent-magnet ECR (Figure 3) ion source
via a cold transfer tube. This configuration is mainly dedicated to gaseous elements that
do not stick on the walls.
Particularly for6He and8He, a special target has been developed which is divided into
two parts because of the long range of He in carbon. The first part, the production target,
induces fragmentation of the carbon primary beam and also fragmentation of carbon
atoms of the target. Helium produced by projectile fragmentation stops in the second part
of the target (the diffusion target) while the He produced by target fragmentation stops
in the production target. The carbon ions of the primary beam that do not react are also
stopped in this first part. By this means, the production target is heated by the primary
beam power, allowing the diffusion of the He atoms produced by the fragmentation of
the carbon atoms of the target, while the diffusion target needs ohmic heating to reach
a suitable temperature for diffusion. Radioactive oxygen beams have been produced by
using the fact that a radioactive oxygen atom produced in the graphite target can combine
with the carbon and produce a CO molecule that diffuses to the ion source. The behaviour
of the ion source has also been studied by comparing the charge state distribution of multi-
charged ions during different moments of the production. It was observed that after a
short delay of out-gassing, the source behaviour is no longer affected by the presence of
the target in its neighbourhood. As expected, the charge state distribution of radioactive
noble gases does not show any difference from that of stable isotopes. Radiation risks,
choice of materials and the reliability of the radioactive ion beam production system have
been taken into account in the design of the production cave. As a consequence, primary
beams impinging on the SPIRAL targets are limited to an intensity of 2 1013pps or 6 kW
of beam power.
The present
3. RADIOACTIVE BEAM INTENSITIES AND RELIABILITY
The intensities of all possible beams available at SPIRAL are permanently updated
in the GANIL web-page [10]. In all cases, off-line reliability tests have been successfully
performed over a long period (more than 20 full days). On-line tests show that the
targets can work for at least 15 days without damage. A list of beams presently provided
at SPIRAL is shown in Table 1.

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SPIRAL at GANIL: Latest Results and Plans for the Future5
The number of 32 experiments were performed at SPIRAL up to July 2006, using 24
TIS. This corresponds to more than 8,000 hours of beam on the production target. The
average ratio between the total beam time scheduled and the beam time actually furnished
to the experiments is about 85 %. Three experiments could not be done due to breaking
of the production system. Two of them were already re-scheduled. Both experiments
successfully obtained data.
The overall efficiency of the system varies with the lifetime of the isotope and the
extraction voltage of the TIS. Typical efficiencies obtained are of the order of 50%, for
diffusion/effusion for atoms of6He (T1/2= 0.8 s) and of 20% for transport and acceleration
at extraction voltages around 20 kV. Typical ionization efficiencies are of 90% for 1+and
of the order of 7% for 2+charge states.
The extraction voltage is tuned depending on the required post-accelerated beam en-
ergy.
After the year 2003 a new target for He beams was developed, for use with 3.0 kW beam,
corresponding to the maximum13C beam intensity available at GANIL. This intensity
allows to obtain the beam intensities for6,8He shown in Table 2.
Table 1
List of presently available beams at SPIRAL.
ElementA
Kr72 73
Ar31 32
Ne 1718
F 18
O 1415
N 1316
He68
The experimental beam intensities are given in ref. [10].
74
33
19
75
34
23
76
35
24
77
41
25
79
42
26
81
43
27
444546
19 202122
Table 2
Measured radioactive beam intensities for He isotopes corresponding to a primary beam
power of 2.5 kW. The quoted numbers were not measured at same extraction conditions.
Beam ChargeLow Energy Yield Accelerated Yield
(pps)(pps)
1+2 108
2.8 107
2+1 107
5 106
1+ 1.3 106
1.8 105
2+6.5 104
5 104
Min. Energy
(A MeV)
3.2
-
3.8
-
Max. Energy
(A MeV)
7.3
20
4.1
15.4
6He
6He
8He
8He

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6A.C.C. Villari, C. Eleon, R. Alves-Cond´ e et al.
4. NEW DEVELOPMENTS
Alkali beams are being developed for SPIRAL. The production principle is based on
projectile fragmentation in a graphite target. The target has approximately the same
design as the previous one, for gaseous elements and compounds. The difference from the
previous design is that a surface ionization ion source is coupled directly to the target
and serves for the production of 1+ions immediately after the radioactive atoms diffusion
out of the target. The ion source is constituted by a carbon tube of 2 cm long and 4
mm diameter, heated independently from the target. After first ionization, the 1+beam
is accelerated and directed to the NANOGAN-3 ECRIS. The 1+beam is afterwards
decelerated to very low energy (of the order of 5 eV) in order to be injected into the ECR
plasma of the ECRIS. After that, the beam will be extracted as multi-charged ions from
the ECRIS and conducted to CIME for further acceleration. In this process no heating
of the transfer tube between the target container and the ion source, as well as the ion
source chamber, is needed. Alkali elements are easily ionized by surface ionization ion
sources with excellent efficiencies and we estimated that the injection of the 1+beams can
also be implemented with efficiencies of the order of 50%, which would give reasonable
performances for the overall production system.
Figure 4. TIS for production of alkali at SPIRAL. In the left side a target is embedded in a
surface ionization ion source. The ECRIS represented on the right is the fully permanent
magnet NANOGAN-3.
It should be noted that in any case, due to the high ECR plasma potential energy, any
ion can only be injected in the ECR plasma if it has sufficient energy to overcome this
barrier. Therefore, a fine tuning is needed for injecting 1+beams into the ECR plasma.

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SPIRAL at GANIL: Latest Results and Plans for the Future7
Table 3
Measured radioactive beam intensities for 1+alkali isotopes using48Ca primary beam at
60A MeV with intensity normalized to 0.14 pµA (400W).
BeamLifetime
(s)
0.84
0.18
59.1
1.07
0.30
394
1.2
17.5
Yield
(pps)
1 106
3.4 104
3 107
6.5 106
9.5 105
1.8 106
7.5 104
1.8 108
Efficiency
(%)
13
2.1
34
18
10
1.2
31
42
8Li
9Li
25Na
26Na
27Na
29Al
37K
47K
That is also the reason why a simple transfer of alkalis via a hot surface tube would not
work: ions, which would be surface ionized along the path between the target and the
ECRIS, would not be able to overcome the plasma barrier. Figure 4 shows the new TIS
system and the short optical beam transfer between the 1+and the ECR ion sources.
Preliminary tests of the surface ionization ion source (the left part of Figure 4) were
performed at SIRa test bench using48Ca primary beam at 60A MeV with intensity of 70
pnA. Table 3 present the obtained yields as well as the overall efficiencies for Li, Na and
K isotopes.
The efficiencies obtained are in good agreement with estimated diffusion/effusion and
ionization using a carbon ionizer. Tests of the overall system, including injection and
extraction of the beam in NANOGAN-3 will be performed in spring 2007. Alkali beams
will be available at SPIRAL in 2008.
5. SUMMARY
SPIRAL (Production System of Radioactive Ion and Acceleration On-Line) facility at
GANIL at Caen has delivered its first beam in September 2001. After working for almost
5 years, 32 experiments were performed in the facility using exotic isotopes of helium,
oxygen, neon, argon and krypton. The intensities of the radioactive beams increased since
the first beam was delivered. Nominal intensity values are achieved for most of noble gas
beams. Developments of new beams as well as the increasing of present intensities for
a number of isotopes are being undertaken. Promising efficiencies were obtained for the
production of Li, Na, K as well as Al isotopes with a new surface ionization ion source,
which will be in the future coupled with the present ECRIS NANOGAN-3.
REFERENCES
1. R. Anne et al., Nucl. Instr. Meth. A257 (1987) 215.

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8A.C.C. Villari, C. Eleon, R. Alves-Cond´ e et al.
2. A.C.C. Villari and the Spiral group, Nucl. Phys. A 693 (2001) 465.
3. R. Lichtenthler et al., Nucl. Instr. Meth. B 140 (1998) 415.
4. L. Maunoury et al., in: 18th.Int. Workshop on ECR Ion Sources, College Station, TX,
USA, 1997.
5. E. Baron, in: 14th. Int. Conf. On Cyclotrons and Their Application, Cape Town,
South Africa, 1995, World Scientific, 1996.
6. R. Anne et al., Proceedings of the Part. Acc. Conf. Washington, USA, 17-21 May
1993.
7. N. Lecesne et al., Nucl. Instr. Meth. in Phys. Res. B 126 (1997) 141.
8. L. Maunoury, Thesis GANIL T97-08, 1997
9. F. Pellemoine, thesis GANIL T01-03, 2001
10. www.ganil.fr