Fabrizio Consoli

UWB Circular Slot Antenna Provided with an Inverted-L Notch Filter for the 5 GHz WLAN Band

Abstract—The study of a planar circular slot antenna for Ultrawideband (UWB) communications is presented. The integration on this antenna of a notch filter, to reduce the possible interferences with the 5GHz WLAN communications, has been discussed in detail. Four different structures, achieved by etching a suitable pattern on the antenna circular stub, have been considered, and their features have been compared. The antenna with symmetrical and inverted-L cuts shows the best performance, and it has been therefore realized and fully characterized. It shows very good matching features over the UWB band, and notable rejection of the 5 GHz WLAN band.

Observations of the frequency tuning effect in the 14 GHz CAPRICE ion source

A set of measurements with the CAPRICE ion source at the GSI test bench has been carried out to investigate its behavior in terms of intensity and shape of the extracted beam when the microwaves generating the plasma sweep in a narrow range of frequency (+/-40 MHz) around the klystron center frequency (14.5 GHz). Remarkable variations have been observed depending on the source and the beamline operating parameters, confirming that a frequency dependent electromagnetic distribution is preserved even in the presence of plasma inside the source. Moreover, these observations confirm that the frequency tuning is a powerful method to optimize the electron cyclotron resonance ion source performances. A description of the experimental setup and of the obtained results is given in the following.

Study on Super-Wideband Planar Asymmetrical Dipole Antennas of Circular Shape

We present a detailed study of a very large band planar circular asymmetrical dipole antenna, fed by a microstrip, for the purpose of covering most of the common communication channels with one solution. The study has been performed on two planar substrates having different dielectric permittivities. The prototype on the substrate with lower permittivity shows much larger bandwidth, and it has been realized and fully characterized, in terms of impedance matching and radiation properties. Its measured band ratio is 21.9:1. The comparison with other super-wideband (SWB) antennas of similar type, with more complex design and therefore required optimization, shows that this prototype has very appealing features of very large absolute bandwidth and band ratio, and a compact size.

Microwave field distribution and electron cyclotron resonance heating process.

In an electron cyclotron resonance ion source, ions are produced from a plasma generated and sustained by microwaves with a proper frequency. Some experiments showed that the plasma formation, the consequent amount of particles extracted from the source, and the related beam shape strongly depend on the frequency of the electromagnetic wave feeding the cavity. In order to have a better understanding of these phenomena, in this work we deal with the description of the motion of a charged particle inside the plasma chamber model of the SERSE ion source operating at INFN-LNS in Catania, the analysis being applicable to any similar apparatus. The electromagnetic fields inside the vacuum filled chamber were determined theoretically and, together with proper simulations, their fundamental role on the particle motion, on their confinement, and on the energy transfer they are subjected to during their motion within the cavity is shown.

Status report of the multipurpose superconducting electron cyclotron resonance ion source

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.

Analysis of the SERSE Ion Output by Using Klystron-based or TWT-based Microwave generators

A set of measurements has been carried out in order to confirm the previously observed enhancement of the SERSE source performances, when microwaves are fed by means of a TWT generator instead of a Klystron generator, which has been commonly used. An increase in the extracted currents takes place for the highest charge states by using a TWT at 14 GHz, while higher extracted currents were obtained for every charge state by using a TWT at 18 GHz. A description of the experimental set‐up and of the obtained results is given in the following. The data will be analysed and a qualitative explanation in terms of ECRIS plasma model will be proposed.

Investigation about the modes in the cylindrical cavity of an ECR ion source

Both theoretical and numerical electromagnetic analyses about the modes inside the cylindrical cavity of superconducting electron cyclotron resonance ion source (SERSE) have been performed. Modes close to 14, 18 and 28 GHz frequencies, usually employed in SERSE operating conditions, have been calculated in vacuum and when the chamber is filled with a uniform non-collisional plasma at different electron densities. To consider the holes present in the chamber flanges, a numerical approach has been used, by means of the HFSSTM electromagnetic simulator, for the first mode in the cavity. Modes in a plasma-filled cylindrical cavity with holed bases have full width half maximum bandwidths larger with regard to the closed cavity in vacuum, and it leads to an increased mode frequency overlap. A monochromatic electromagnetic wave feeding this cavity can, in principle, excite different modes. Further investigations about the coupling between the SERSE cavity and its feeding waveguides have to be performed.

Perspectives for the ECLISSE method with third generation ECRIS

The ECLISSE experiment performed at INFN-LNS in 2002 with the superconducting ECR ion source SERSE proved the possibility to couple a laser ion source (LIS) with an electron cyclotron resonance ion source (ECRIS) in order to obtain cw ion beams from refractory metals with characteristics that are not achievable with standard LIS. The oven that is used for the production of vapors inside the ECRIS fails with refractory elements and the sputtering method is not adequate for the production of beams with intensity above a few tens of micro ampere. So the use of a LIS inside the ECRIS plasma chamber may permit to obtain the advantage of a LIS in terms of beam current with the typical features of an ECRIS (high charge states, cw mode operation, relatively low emittance). One of the limiting factors of the previous experiment was the relatively low plasma density of the previous generation ECRIS, working at a frequency between 14 and 18 GHz. Nowadays the availability of third generation ECRIS (operating at 28 GHz or higher, i.e. with a plasma density four times larger) may extend the capabilities of this method, as the denser plasma may catch ions from LIS with energies up to about 1 keV per charge state, much higher than it is possible for sources operating at lower frequency (e.g. about 200 eV per charge state for the SERSE source). The perspectives opened by the availability of MS-ECRIS source operating at 28 GHz will be described along with some details on the proposed experimental programme, to be carried out in 2008 at GSI, Darmstadt.

Model for calculation of ion charge-state distribution in ECR ion source plasma

The investigation of the widespread 0D fluid model Ref. 1 - Ref. 8 for calculation of ion charge-state distributions (CSD) in electron cyclotron resonance (ECR) ion source Ref. 1 is presented. The modification of this model that allows one to describe the confinement and accumulation processes of highly charged ions in ECR plasma for gas mixing case more precisely is discussed. The description of the calculation technique for the time confinement of ions and electrons based on the theory of Pastukhov is also given, videlicet - calculation of confinement times during two stage minimization scheme of special functionals. The results obtained by this approach have been compared with available experimental data.

Dependence on Frequency of the Electromagnetic Field Distribution inside a Cylindrical CavityExcited through an Off-Axis Aperture

To explain the relevant changes in the electron cyclotron resonance ion source behaviour for small variations of the exciting radiation frequency, we determine the spatial distribution of the field within the cavity for every resonant mode.