The major infrastructures of nuclear physics in Europe adopted the technology of electron cyclotron resonance (ECR) ion sources for the production of heavy-ion beams. Most of them use 14 GHz electron cyclotron resonance ion sources (ECRISs), except at INFN-LNS, where an 18 GHz superconducting ECRIS is in operation. In the past five years it was demonstrated, in the frame of the EU-FP5 RTD project called "Innovative ECRIS," that further enhancement of the performances requires a higher frequency (28 GHz and above) and a higher magnetic field (above 2.2 T) for the hexapolar field. Within the EU-FP6 a joint research activity named ISIBHI has been established to build by 2008 two different ion sources, the A-PHOENIX source at LPSC Grenoble, reported in another contribution, and the multipurpose superconducting ECRIS (MS-ECRIS), based on fully superconducting magnets, able to operate in High B mode at a frequency of 28 GHz or higher. Such a development represents a significant step compared to existing devices, and an increase of typically a factor of 10 for the intensity is expected (e.g., 1 emA for medium charge states of heavy ions, or hundreds of e$\mu$A of fully stripped light ions, or even 1 e$\mu$A of charge states above $50^+$ for the heaviest species). The challenging issue is the very high level of magnetic field, never achieved by a minimum B trap magnet system; the maximum magnetic field of MS-ECRIS will be higher than 4 or 5 T for the axial field and close to 2.7 T for the hexapolar field. The detailed description of the MS-ECRIS project and of its major constraints will be given along with the general issues of the developments under way
The possibility of increasing the electron cyclotron resonance (ECR) plasma electron density by secondary electron emission has already been pointed out and tested by different authors. In this work the effective secondary electron emission coefficient σeff under electron impact was measured and its evolution studied as a function of the primary electron beam energy and intensity of the target bias. The usual parameters of the ECR plasma such as the electron temperature, the plasma electric potential, and the ambipolar diffusion effects in the ECR plasma chamber have been considered during these measurements. With that end in view a research facility delivering electron beams with energies in the 0–15 keV range and intensities in the 1×10−11–2×10−5 A range was developed. The study of the effective secondary electron emission coefficient σeff was carried out on different targets made of graphite, of metals such as pure and technical Al, Ta, Ni, stainless steel, and of metal-dielectric structures Al–Al2O3. For some Al–Al2O3 structures high values of σeff strongly dependent upon the primary electron beam energy and intensity and upon the target negative bias have been obtained. Such a dependence was not observed for metals. The use of highly emissive metal-dielectric structures in the plasma chamber of an ECRIS should lead to a significant enhancement of the ECR plasma electron density and consequently of the production of highly charged ions.
In previous research we have demonstrated that metal–dielectric (MD) structures have high capabilities to enhance the high-charge-state ion production in electron cyclotron resonance ion sources. In order to explain this effect, dedicated experiments have been performed, in which changes of main plasma parameters in the presence of a MD structure have been observed and an explanation for the mechanism of this “MD effect” was given. In this contribution we present a new experiment where we have concentrated on the question whether the effect of the high-charge-state enhancement by the MD structures is due to the presence of just a dielectric layer in the plasma chamber (e.g., working simply as a breaking of the nonambipolar wall currents) or whether details of the structure of the layer play an essential role. By comparing ion charge state distributions and bremsstrahlung spectra for two MD cylinders, of drastically different layer thicknesses, the importance of the MD effect, and hence, of the detailed structure of this type of layer for the production of very highly charged ions is demonstrated.
Intense heavy ion beam production with electron cyclotron resonance (ECR) ion sources is a common requirement for many of the accelerators under construction in Europe and elsewhere. An average increase of about one order of magnitude per decade in the performance of ECR ion sources was obtained up to now since the time of pioneering experiment of R. Geller at CEA, Grenoble, and this trend is not deemed to get the saturation at least in the next decade, according to the increased availability of powerful magnets and microwave generators. Electron density above 10(13) cm(-3) and very high current of multiply charged ions are expected with the use of 28 GHz microwave heating and of an adequate plasma trap, with a B-minimum shape, according to the high B mode concept [S. Gammino and G. Ciavola, Plasma Sources Sci. Technol. 5, 19 (1996)]. The MS-ECRIS ion source has been designed following this concept and its construction is underway at GSI, Darmstadt. The project is the result of the cooperation of nine European institutions with the partial funding of EU through the sixth Framework Programme. The contribution of different institutions has permitted to build in 2006-2007 each component at high level of expertise. The description of the major components will be given in the following with a view on the planning of the assembly and commissioning phase to be carried out in fall 2007. An outline of the experiments to be done with the MS-ECRIS source in the next two years will be presented.
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