Time resolved characterization of plasma X-ray emission represents an innovative technique to characterize non-equilibrium phases in Electron Cyclotron Resonance Ion Sources (ECRIS). Indeed, although ...ECRIS plasmas are usually in dynamical equilibrium, many relevant phenomena are characterized by fast transients and require a dedicated diagnostics to be fully investigated. In particular, time resolved diagnostics can be applied to characterize the X ray emission during the plasma turn on and off and during the turbulence phenomena induced by Cyclotron-Maser instability. This paper presents the experimental set-up used during the last campaign at measurement carried out at the Istituto Nazionale Fisica Nucleare -Laboratori Nazionali del Sud (INFN-LNS), together with the main achieved results. Particular relevance will be given to the characterization of the afterglow phase, which highlighted the existence of two electron populations characterized by different mean lifetime. Evidences of X-ray bursts emission in the afterglow phase, compatible with Cyclotron Maser instability, will be also shown.
Microwave-to-plasma coupling in ECRIS has been based on the classic scheme of waveguide-to-cylindrical plasma cavity matching. Optimization has been often obtained by empirical adjustments leading to ...an oversimplified model, though obtaining satisfactory performances. In order to overcome the ECR-heating paradigm, on-purpose design of launchers' setup and adequate diagnostics are going to be developed at INFN. This paper describes three-dimensional numerical simulations and Radio Frequency (RF) measurements of wave propagation in the microwave-heated magnetized plasmas of ion sources. Moreover, driven by an increasing demand of high frequency ECR ion sources, innovative ideas for the geometry for both the plasma chamber and the related RF launching system—in a microwave absorption-oriented scenario—are presented. Finally, the design of optimized launchers enabling “single-pass” power deposition, not affected by cavity walls effects, are described.
This work presents the multiple diagnostics characterization of the plasma in an axis-symmetric simple mirror trap as a function of magnetic field profile (mirror ratios and magnetic field gradient), ...especially in the quasi-flat B field configuration that is typical of Microwave Discharge Ion Sources, and also of neutral gas pressure and microwave power. The simultaneous use of Optical Emission Spectroscopy, Langmuir Probe and X-ray diagnostics allows the characterization of the whole electron energy distribution function (EEDF), from a few eV to hundreds of keV . Results show non-linear behaviour under small variations of even one source parameter and strong influence on EEDF of the Bmin/BECR ratio. Benefit and next developments will be highlighted.
At the Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Sud (INFN-LNS), the commissioning of the high intensity proton source for the European Spallation Source (PS-ESS) has been ...recently completed. Optical emission spectroscopy measurements carried out with PS-ESS permitted, in a noninvasive way, the evaluation of the electron density, temperature, and relative abundances of the neutral components of a hydrogen plasma. This approach is helpful in finding the optimal source parameters exploiting protons orH2+beams production.
Magnetoplasmas in ECR-Ion Sources are excited from gaseous elements or vapours by microwaves in the range 2.45–28 GHz via Electron Cyclotron Resonance. A B-minimum, magnetohydrodynamic stable ...configuration is used for trapping the plasma. The values of plasma density, temperature and confinement times are typically ne=1011−1013 cm−3, 01eV<Te<10 keV, 0.001<tc<1 s. At INFN-LNS several diagnostics tools have been developed for probing the electromagnetic emission of such plasmas, in the optical/X-ray domain. Fast Silicon Drift detectors with high energy resolution of 125 eV at 5.9 keV have been used for the characterization of plasma emission at 02<E<3 keV . In the domain 0.4–17 keV an X-ray pin-hole camera technique has allowed space resolved X-ray spectroscopy with a spatial resolution down to 30 μm and an energy resolution down to 140 eV at 5.9 keV . In parallel, imaging in the optical range and spectroscopic measurements have been carried out. Relative abundances of H/H2 atoms/molecules in the plasmas have been measured for different values of neutral pressure, microwave power and magnetic field profile (they are critical for high-power proton sources).
Optical Emission Spectroscopy (OES) represents a very reliable technique to carry out non-invasive measurements of plasma density and plasma temperature in the range of tens of eV. With respect to ...other diagnostics, it also can characterize the different populations of neutrals and ionized particles constituting the plasma. At INFN-LNS, OES techniques have been developed and applied to characterize the plasma generated by the Flexible Plasma Trap, an ion source used as "testbench" of the proton source built for European Spallation Source. This work presents the characterization of the parameters of a hydrogen plasma in different conditions of neutral pressure, microwave power and magnetic field profile, along with perspectives for further upgrades of the OES diagnostics system.
A numerical tool for analysing spatially anisotropic electron populations in electron cyclotron resonance (ECR) plasmas has been developed, using a trial-and-error electron energy distribution ...function (EEDF) fitting method. The method has been tested on space-resolved warm electrons in the energy range \(2-20\,\mathrm{keV}\), obtained from self-consistent simulations modelling only electron dynamics in ECR devices, but lacked real-world validation. For experimentally benchmarking the method, we attempted to numerically reproduce the experimental X-ray emission spectrum measured from an argon plasma. Results of this analysis have provided crucial information about density and temperature of warm electrons, and competing distributions of warm and hot electron components. This information can be fed back to simulation models to generate more realistic data. Subsequent application of the numerical tool as described to the improved simulation data can result in continuous EEDFs that reflect the nature of charge distributions in anisotropic ECR plasmas. These functions can be also applied to electron dependent reactions, in order to reproduce experimental results, like those concerning space-dependent K\(\alpha\) emissions.
The Electron Cyclotron Resonance Ion Sources (ECRIS) are nowadays the most effective devices to provide relatively intense currents for highly charged ions devoted to particle accelerators for ...nuclear science and applications. In ECRIS, the main mechanism of microwave-to-electrons energy transfer is the Electron Cyclotron Resonance heating, when electrons gyrofrequency f ce =eB/(2πm e ) equals the frequency f μwave of the injected microwaves. In ECR plasmas, because of the low electron-ion collision cross-section, the ions remain cold (few eV or less). A direct mastering of the ion temperature through Ion Cyclotron Resonance Heating (ICRH) could be relevant both for improving the performances of the ECRIS as well as for fundamental Physics. In this latter case, the aim is to investigate nuclear decays as a function of the ionization state or the ion temperature. In this paper, the modeling of Radio Frequency (RF) wave-plasma interactions in the ICRH range is investigated for the first time in a compact ECR, B-minimum plasma trap. RF field computation - based on a 3D full-wave FEM-based code - is able to predict wave propagation and power absorption in a non-uniform "cold" anisotropic plasma bounded by a metallic resonator and immersed in a magnetic configuration typical of ECR ion sources. Moreover, some technological aspects and a conceptual design of the RF antenna and related systems delivering multi-kilowatts of power to the plasma ion component are discussed.
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