EXPERIMENTAL CHARACTERIZATION OF AN OVERDENSE PLASMA IN A COMPACT ION SOURCE

Electron Cyclotron Resonance Ion Sources (ECRIS) are compact plasma-based machines able to feed particle accelerators with high intensity beams of multi-charged ions. ECRIS plasmas are density-limited, since they are sustained by E.M. wave propagation up to a cut-off density value. In the past, the only way to improve ECRIS performance was to increase the microwave frequency and the magnetic field strength to satisfy the ECR condition. A different plasma heating mechanism is being applied at INFN-LNS. It is based on Electron Bernstein Waves (EBW), i.e., electrostatic waves which do not suffer any density cut-off. Highlights concerning preliminary signatures of EBW formation and subsequent absorption are given here

3D-full wave and kinetics numerical modelling of electron cyclotron resonance ion sources plasma: Steps towards self-consistency

<p>Electron Cyclotron Resonance (ECR) ion Sources are the most performing machines for the production of intense beams of multi-charged ions in fundamental science, applied physics and industry. Investigation of plasma dynamics in ECRIS still remains a challenge. A better comprehension of electron heating, ionization and diffusion processes, ion confinement and ion beam formation is mandatory in order to increase ECRIS performances both in terms of output beams currents, charge states, beam quality (emittance minimization, beam halos suppression, etc.). Numerical solution of Vlasov equation via kinetic codes coupled to FEM solvers is ongoing at INFN-LNS, based on a PIC strategy. Preliminary results of the modeling will be shown about wave-plasma interaction and electron-ion confinement: the obtained results are very helpful to better understand the influence of the different parameters (especially RF frequency and power) on the ion beam formation mechanism.</p&gt

Electron cyclotron resonance ion source plasma characterization by X-ray spectroscopy and X-ray imaging

<p>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.</p&gt

Plasma Induced Variation of Electron Capture and Bound-State β\beta Decays

The slow neutron capture ($s$-process) synthesises ~50% of all elements in the universe heavier than iron, whose abundances are determined by the competition between neutron capture and nuclear $\beta$-decay rates. The latter are expected to vary inside hot and dense plasmas such as those found in $s$-process nucleosynthesis sites. Here, we present a new and general theoretical study of the effect of local and non-local thermodynamic equilibrium ((N)LTE) plasmas on $\beta$-decays, using orbital electron capture (EC) decays in $^{7}$Be as a model case. We begin from the model of Takahashi and Yokoi to calculate the lepton phase volume of $^{7}$Be as a function of its ionisation state and excitation level, and consequently, the configuration-dependent EC decay rate. We then calculate the in-plasma ion charge state distribution (CSD) and level population distribution (LPD) for a grid of plasma density and temperatures, using the population kinetics code FLYCHK. By combining the configuration-dependent EC rate with the CSD and LPD, we calculate the in-plasma orbital EC rate in $^{7}$Be. The results show a strong correlation between the half-life and thermodynamic conditions of the plasma, underlining the importance of measuring decay rates in laboratory plasmas and the relevance of high precision atomic configuration models. The model discussed in this work is capable of calculating EC and bound state $\beta$ decay (BSBD) rates in both low-density NLTE and high-density LTE plasmas. We conclude by validating our model with state-of-the-art data in literature on isotopes of Pr and Dy, and by proposing future extension of the model to laboratory magnetoplasmas and stellar interiors aimed at improving nucleosynthesis models.Comment: 24 pages, 12 figures, 2 tables. Submitted to Nature Communication

Electromagnetic analysis of the plasma chamber of an ECR-based charge breeder.

The optimization of the efficiency of an ECR-based charge breeder is a twofold task: efforts must be paid to maximize the capture of the injected 1+ ions by the confined plasma and to produce high charge states to allow post-acceleration at high energies. Both tasks must be faced by studying in detail the electrons heating dynamics, influenced by the microwave-to-plasma coupling mechanism. Numerical simulations are a powerful tools for obtaining quantitative information about the wave-to-plasma interaction process: this paper presents a numerical study of the microwaves propagation and absorption inside the plasma chamber of the PHOENIX charge breeder, which the selective production of exotic species project, under construction at Legnaro National Laboratories, will adopt as charge breeder. Calculations were carried out with a commercial 3D FEM solver: first, all the resonant frequencies were determined by considering a simplified plasma chamber; then, the realistic geometry was taken into account, including a cold plasma model of increasing complexity. The results gave important information about the power absorption and losses and will allow the improvement of the plasma model to be used in a refined step of calculation reproducing the breeding process itself