C. Eleon

The radioactive ion beam production systems for the SPIRAL2 project

The SPIRAL2 project, currently under construction at GANIL, will include an isotope separator on line based facility for the production and acceleration of radioactive ion beams. A superconducting linear accelerator will accelerate 5 mA deuterons up to 40 MeV and 1 mA heavy ions up to 14.5 MeV/u. These primary beams will be used to bombard both thick and thin targets. We are investigating three different techniques to produce the radioactive ion beams: (1) the neutron induced fission of uranium carbide, (2) the direct interaction of deuterons in a uranium carbide target, and (3) the interaction of a heavy ion beam with a target. All these production systems will be coupled to an ion source. Four kinds of ion sources are foreseen for the ionization of the radioactive atoms: an electron cyclotron resonance ion source, a surface ionization ion source, a forced electron beam induced arc discharge ion source, and a laser ion source depending on the characteristics of the desired radioactive ion beam in terms of intensity, efficiency, purity, etc. A presentation of the SPIRAL2 project and of the different production systems is given.

Nuclear charge radius of He8

The root-mean-square (rms) nuclear charge radius of 8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from 6He to 8He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.

Total efficiency of an isotope-separator-on-line production system based on an electron cyclotron resonance ion source associated with a carbon target: The case of SPIRAL 1

An original approach to the time behavior of an isotope-separator-on-line production system is proposed in the case of a production system where the target and the ion source are connected through a conductance much larger than that of the exit hole of the source. One major goal of this article is to derive the analytical expression of the response time of the system for noble gases from statistical parameters only, which can be deduced from a few simple measurements. The validity limits of the expression of the total efficiency are given, and the calculations are compared to the results obtained at GANIL during operation of SPIRAL 1, using a carbon target close coupled to a multicharged electron cyclotron resonance ion source. The final analytical expression for the total efficiency shows that the usual product of diffusion efficiency, effusion efficiency, and ionization efficiency cannot be applied in our case. We show how it is possible to predict the atom-to-ion transformation efficiency for radioactive isotopes of noble gas using response times measured for stable isotopes.

Status report of stable and radioactive ion beam production at GANIL.

GANIL has been producing many stable and radioactive ion beams for nearly 25 years. Constant progresses have been made in terms of intensity, stability, and reliability. The intensity for some stable metallic beams now exceeds or approaches the p microA level at an energy up to 95 MeV/u, e.g., 1.14 p microA for (36)S (65% enriched) at 77 MeV/u, 0.35 p microA for (58)Ni (63% enriched) at 74 MeV/u. Some recent results with Magnesocene using the metallic ions from volatile compounds method should also make possible the production of metallic beams with an intensity greater than 1 p microA. This has still to be measured. The ISOL facility SPIRAL I has been in operation for almost six years. Up to now, 17 exotic He experiments have been done with 14 target/ion-source (TIS) units; 19 other experiments (with O, Ne, Ar, and Kr) have been achieved with 14 TISs. Statistics show a fairly good ratio of available beam time to scheduled beam time. The radioactive beams and available intensities are compiled in this report. Future developments on radioactive ion beam production are briefly presented, while more details will be discussed elsewhere at this conference.

Production of high intensity primary beams at GANIL

The 100kV platform used for the production of primary beams has been modified in order to increase the beam intensity. The configuration of the new platform is described and preliminary results are reported. A gain intensity of a factor of 2 has already been obtained for sulfur: S36 (65% enriched) 3.2kW at 77.5MeV∕u, i.e., 1.14pμA, as well as for nickel: Ni58 (68%) 1.5kW at 74.5MeV∕uA, i.e., 0.35pμA.

Direct 1+ to n+ method for production of radioactive alkaline ions

In the frame of the production of radioactive ion beams by isotope separator on line method, a new principle of target∕ion-source system has been developed at GANIL to produce multicharged ions of alkalis. The principle consists of a surface ionization source associated to a multicharged electron-cyclotron-resonance ion source (ECRIS) named NANOGAN III [R. Leroy et al., AIP Conf. Proc. 749, 137 (2004)] presently used to produce radioactive ions of gas on Systeme de Production d’Ions Radioactifs Acceleres en Ligne partie I. The singly charged ions are injected in the multicharged ion source without mass separation, through a very short beam line including several stages of acceleration, focusing, deceleration, and rf injection. The first tests showed a good behavior of the ECRIS with the new rf coupling. A study of the surface ionization source is in progress in order to improve its coupling to the 1+ beam line.

Nuclear Charge Radius ofHe8

The root-mean-square (rms) nuclear charge radius of 8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from 6He to 8He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.

Radio frequency injection system for electron-cyclotron-resonance ion source in a hostile environment

In the framework of the Systeme de Production d’Ions Radioactifs Acceleres en Ligne Phase II (SPIRAL II) project, one of the ion sources which produce 1+ ions is an electron-cyclotron-resonance ion source (ECRIS). The source is installed in a region where the dose rate is such that the radiation hardness is very important for the materials used. Moreover, the proximity of the UCx target leads to additional constraints as potential surface pollution. A radiation-hard ECRIS has been designed, and the rf injection is under study. The results of rf injection with a wave guide and with an antenna will be presented. The performance obtained with both injection systems combined with the environmental constraints have led us to inject the rf using an antenna. The last point consists in designing a wave guide able to transport the rf through the shielding of the SPIRAL II plug. Design constraints, tests, and the current state of the project will be presented.

Direct 10 GHz rf feedthrough plasma device with the NANOGAN III ion source for SPIRAL

A new system has been designed to inject the 10 GHz rf power in the NANOGAN III ion source dedicated to the ionization of exotic atoms from the production target of the SPIRAL system at GANIL. The present system, based on a rectangular-to-coaxial transition equipped with a tuning piston, has been replaced by a direct rectangular-to-circular wave guide to feed the plasma of the source. We present the constraints related to the rf injection and a comparison is given of the present and new injection systems.