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The ion sources for accelerators devoted to medical applications must provide intense ion beams, with high reproducibility, stability and brightness. AISHa (Advanced Ion Source for Hadron therapy) is a compact ECRIS whose hybrid magnetic system consists of a permanent Halbach-type hexapole magnet and a set of independently energized superconducting coils. These coils will be enclosed in a compact cryostat with two cryocoolers for LHe-free operation. The AISHa ion source has been designed by taking into account the typical requirements of hospital-based facilities, where the minimization of the mean time between failures (MTBF) is a key point together with the maintenance operations which should be fast and easy. It is a multipurpose device, operating at 18 GHz, in order to achieve higher plasma densities able to provide enough versatility for future needs of the hadron therapy, including the ability to run at larger microwave power to produce different species and highly charged ion beams. In this paper, the innovative solutions, used for the plasma containment chamber and for the permanent magnet hexapole holder, are presented to solve the insulation and structural issues. The choice of the different materials used is hereinafter discussed together with all the involved processes (spinning, curing and machining). The glass fibers and carbon fibers are used to reinforce polymer matrices and give rise to structural composites and composites by molding. The paper shows also some results of ion source commissioning along with next developments. Innovative active coupling techniques are planned to be tested to optimize the first pass wave absorption, which plays an important role in the coupling optimization of the new-generation ECRIS. [ABSTRACT FROM AUTHOR]

This paper describes 3-D numerical simulations and radio frequency (RF) measurements of wave propagation in microwave-heated magnetized plasmas of ion sources. Full-wave solution of Maxwell’s equations has been addressed through the finite-element method commercial software COMSOL. Our numerical model takes into account the strongly inhomogeneous and anisotropic magnetized “cold” plasma medium. The simulations reproduce the main features of the wave–plasma interaction of the flexible plasma trap (FPT) that recently came into operations at INFN-LNS. A two-pin RF probe has been ad hoc developed and used as a plasma-immersed antenna for measuring local wave electric fields in the FPT device. The measurements of plasma electron density and RF electric field, performed for different external magnetic field configurations, allowed direct comparison with the assumed simulation model. [ABSTRACT FROM AUTHOR]

The Electron Cyclotron Resonance Ion Sources (ECRISs) development is strictly related to the availability of new diagnostic tools, as the existing ones are not adequate to such compact machines and to their plasma characteristics. Microwave interferometry is a non-invasive method for plasma diagnostics and represents the best candidate for plasma density measurement in hostile environment. Interferometry in ECRISs is a challenging task mainly due to their compact size. The typical density of ECR plasmas is in the range 1011-1013 cm-3 and it needs a probing beam wavelength of the order of few centimetres, comparable to the chamber radius. The paper describes the design of a microwave interferometer developed at the LNS-INFN laboratories based on the so-called "frequency sweep" method to filter out the multipath contribution in the detected signals. The measurement technique and the preliminary results (calibration) obtained during the experimental tests will be presented. [ABSTRACT FROM AUTHOR]

An experimental campaign aiming to investigate electron cyclotron resonance (ECR) plasma X-ray emission has been recently carried out at the ECRISs-Electron Cyclotron Resonance Ion Sources laboratory of Atomki based on a collaboration between the Debrecen and Catania ECR teams. In a first series, the X-ray spectroscopy was performed through silicon drift detectors and high purity germanium detectors, characterizing the volumetric plasma emission. The on-purpose developed collimation system was suitable for direct plasma density evaluation, performed "on-line" during beam extraction and charge state distribution characterization. A campaign for correlating the plasma density and temperature with the output charge states and the beam intensity for different pumping wave frequencies, different magnetic field profiles, and single-gas/gas-mixing configurations was carried out. The results reveal a surprisingly very good agreement between warm-electron density fluctuations, output beam currents, and the calculated electromagnetic modal density of the plasma chamber. A charge-coupled device camera coupled to a small pin-hole allowing X-ray imaging was installed and numerous X-ray photos were taken in order to study the peculiarities of the ECRIS plasma structure. [ABSTRACT FROM AUTHOR]

The improvement of highly charged ion production with the use of two-frequency heating (TFH) in electron cyclotron resonance ion sources (ECRISs) was observed for the first time already in 1994, but the process has not been explained in details yet. The increase of the ionization rate because of the presence of two resonance surfaces instead of one is clear but not the relation between the two frequencies and the relative weight in terms of power. A series of numerical simulations about the heating process in ECR plasmas has been carried out at INFN-LNS, based on a single particle approach. They allow one to give a reasonable explanation of the TFH of the plasma electrons in terms of the microwave field distribution over the resonance surface, which changes with the excited mode, i.e., with the frequency. By analyzing the results, some considerations about the phase relationship between the electron's gyromotion and the electromagnetic wave can be done, taking into account the stochastic heating theory of ECR plasmas. The phase difference between the two waves in this case is shown to play a role. Finally, the analysis of the simulations' output will give the possibility to explain a great deal of experimental results concerning the multifrequency heating of plasmas in ECRIS. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]