Abstract We present a numerical study of metals dynamics evaporated through resistively heated ovens in electron cyclotron resonance (ECR) plasma traps, used as metal ion beam injectors for ...accelerators and multi-disciplinary research in plasma physics. We use complementary numerical methods to perform calculations in the framework of the PANDORA trap. The diffusion and deposition of metal vapours at the plasma chamber’s surface are explored under molecular flow regime, with stationary and time-dependent particle fluid calculations via COMSOL Multiphysics®. The ionisation of vapours is then studied in the strongly energised ECR plasma. We have developed a Monte Carlo (MC) code to simulate the in-plasma metal ions’ dynamics, coupled to particle-in-cell simulations of the plasma physics in the trap. The presence of strongly inhomogeneous plasmas leads to charge-exchange and electron-impact ionisations of metals, in turn affecting the deposition rate/pattern of the metal on the walls of the trap. Results show how vapours dynamics depends both on evaporated metals and the plasma target. The 134 Cs, 176 Lu, and 48 Ca isotopes were investigated, the first two being radioisotopes interesting for the PANDORA project, and the third as one of the most required rare isotope by the nuclear physics community. We present an application of the study: MC computing the γ activity due to the deposited radioactive neutral nuclei during the measurement time, we quantitatively estimated the overall γ -detection system’s efficiency using GEANT4, including the poisoning γ -signal from the walls of the trap, relevant for the γ -tagging of short-lived nuclei’s decay rate in the PANDORA experiment. This work can give valuable support both to the evaporation technique and plasma source optimisation, for improving the metal ion beam production, avoiding huge deposit/waste of metals known to affect the long-term source stability, as well as for radio-safety aspects and reducing material waste in case of rare isotopes.
Abstract
In this paper we present the numerical design and simulation of RF antennas to be employed in Ion Cyclotron Resonance Heating (ICRH) systems working in ECRIS environment. A 3D full-wave ...numerical model, based on the coupling between COMSOL FEM solution of Maxwell equations and the MATLAB-computed non-homogeneous plasma dielectric tensor, has been employed in order to study the performances of several ICRH antennas. Results in terms of S-parameters, on-axis electric field and RF absorbed power inside the plasma chamber have been obtained and compared between the chosen antenna geometries. The presented study will permit to better understand the fundamental aspects of ion dynamics in ECRISs as well as allowing the design of a proper matching network between the RF amplifier and the antenna, necessary to cope with the plasma properties’ fast variations. Further ion kinetic simulations are ongoing.
Abstract Metals can be injected into electron cyclotron resonance ion sources (ECRIS) via different techniques, among which resistive ovens are used to vaporize neutral materials, later captured by ...the energetic plasma that will step-wise ionize them, hence giving multiply charged ion beams for accelerators. Recently, PANDORA, a novel ECR plasma trap, has been conceived to perform interdisciplinary research spanning from nuclear physics to astrophysics, where in-plasma high charge states of metallic species are demanded. However, a full knowledge on the vaporization method and on the coupling of neutral atoms with plasma and its overall dynamics is still not available. Simulations, hence, are of fundamental relevance to improve the overall efficiency, reduce consumption of rare expensive isotopes, and to improve the ion source performance. We present a numerical study about metallic species suitable for oven injection in ECRIS, focusing on metals diffusion, transport, and wall deposition under molecular flow regime. We studied the metal dynamics with and without plasma. Results underline the plasma role on a space-dependent conversion yield, reflecting the strongly inhomogeneous ECR plasma. The plasma and its parameters have been modelled using an established self-consistent particle-in-cell model. The numerical tool is conceived for the PANDORA plasma trap but can be extended to other ECR plasmas and traps. As test cases we studied the 134 Cs and 48 Ca radioisotopes, as metals of interest for the modern nuclear physics. A focus is given on the β -decaying 134 Cs, as an application case for PANDORA, providing quantitative estimates of the γ-detection signal-poisoning effect by neutral metals deposition at the chamber wall.
Abstract The two-close frequency heating (TCFH) is a new implementation of the well-known two frequency heating. In TCFH, the two frequencies differ around 200-300 MHz each other in order to ...establish two contiguous ECR resonance zones. TCFH has been proved to be a powerful technique to suppress plasma instabilities in Electron Cyclotron Resonance Ion Sources (ECRIS), as well as to improve their performances. Its beneficial effect, compared to the application of a single frequency, is always deduced from the extracted charge states distributions and from the detection of the plasma self-emission in the X-ray and microwave ranges. This paper presents the first approach to a numerical description of the two-close frequency effect, based on the relevant plasma parameters of the ECRIS setup operating at ATOMKI-Debrecen. Simulations have been performed by our PIC-Full Wave code, joining electron kinetics and FEM solution of Maxwell equations in a cold plasma model. Results on plasma electron density and energy distribution will be shown, together with a direct comparison with the already published data on X ray emission.
Abstract Simulations are a powerful method to study the correlation between output beams and internal dynamics of electron cyclotron resonance ion sources (ECRIS), which involve a complex interplay ...between injected power, RF frequency, gas type and pressure. We present here some details on 3D full-wave Particle-in-Cell (PIC) code suites that can simulate electron and ion dynamics self-consistently in an ECR plasma. Preliminary runs of the simulation show an encouraging match with experimental data which acts as a benchmark for the PIC codes and highlights its potential for fundamental and applied interdisciplinary plasma research.
Abstract An innovative ECR ion trap facility, called PANDORA (Plasma for Astrophysics, Nuclear Decay Observation and Radiation for Archaeometry), was designed for fundamental plasma processes and ...nuclear physics investigations. The overall structure consists of three subsystems: a) a large (70 cm in length, 28 cm in inner diameter) ECR plasma trap with a fully superconducting B-minimum magnetic system (B max = 3.0 T) and an innovative design to host detectors and diagnostic tools; b) an advanced non-invasive plasma multidiagnostics system to locally characterize the plasma thermodynamic properties; c) an array of 14 HPGe detectors. The PANDORA facility is conceived to measure, for the first time, in-plasma β -decaying isotope rates under stellar-like conditions. The experimental approach consists in a direct correlation of plasma parameters and nuclear activity by disentangling - by means of the multidiagnostic system that will work in synergy with the γ-ray array - the photons emitted by the plasma (from microwave to hard X-ray) and γ-rays emitted after the isotope β -decay. In addition to nuclear physics research, fundamental plasma physics studies can be conducted in this unconventional ion source equipped with tens of detection and diagnostic devices (RF polarimeter, optical emission spectroscopy (OES), X-ray imaging, space and time-resolved spectroscopy, RF probes, scope), with relevant implications for R&D of ion sources for accelerator physics and technology. Several studies have already been performed in downsized nowadays operating ECRIS. Stable and turbulent plasma regimes have been described quantitatively, studying the change of plasma morphology, confinement, and dynamics of losses using space resolved X-ray spectroscopy.
Abstract
Resistive oven technique is used to inject vapours of metallic species in electron cyclotron resonance (ECR) plasma traps, where plasma provides step-wise ionization of neutral metals, ...producing charged ion beams for accelerators. We present a numerical survey of metallic species suitable for oven injection in ECR ion sources, studying neutrals diffusion and deposition under molecular flow regime. These aspects depend on geometry of the evaporation inlet, thermodynamics, and plasma parameters, which strongly impact on ionization and charge-exchange rate, thus on the fraction of reacting neutrals. We considered diffusion of metals with and without plasma. The plasma and its parameters have been modelled considering an established self-consistent particle-in-cell model. Numerical predictions might be relevant to reduce the metal consumption, to increase the overall efficiency, and to improve the plasma ion source performances. As test case, we studied the
134
Cs isotope, as one of the alkali metals of interest for the modern nuclear physics.
Aim of the PANDORA (Plasmas for Astrophysics, Nuclear Decays Observation and Radiation for Archeometry) project is the in-plasma measurements of decay rates of beta radionuclides as a function of the ...ionization stage. In this view, a precise calculation of plasma electrons density and energy is mandatory, being responsible for ions’ creations and their spatial distribution following plasma neutrality. This paper describes the results of the INFN simulation tools applied for the first time to the PANDORA plasma, including electromagnetic calculations and electrons’ dynamics within the so-called self-consistent loop. The distribution of the various electrons’ population will be shown, with special attention to the warm component on which depends the obtained ions’ charge state distribution. The strict relation of the results with the evaluation of the in-plasma nuclear decays will be also explained.
Abstract
One possible way to optimize microwave coupling and plasma confinement in Electron Cyclotron Resonance (ECR) Ion Sources is a revolutionary design strategy of plasma chambers, breaking the ...cylindrical symmetry. This contribution reports about the design and numerical validation of an innovative resonant cavity playing as plasma chamber of ECR ion sources. The new chamber, named IRIS (Innovative Resonators for Ion Sources), was argued starting from the 3D structure of the plasma and, therefore, fashioned to the twisting magnetic structure. The microwave launching scheme was radically changed as well, consisting of side-coupled slotted-waveguides with diffractive apertures smoothly matching the overall structure of the camera. This approach also enables a profound optimization of cooling systems and overall spaces in general (for gas feedings, oven systems, sputtering, etc.). Here we report on the conceptual study, electromagnetic design and PIC simulations of the electron heating in the novel resonant cavity, comparing results with those for standard (cylindrical) chamber, and also considering the impact of microwave feeding led by single aperture rectangular waveguides vs. waveguide-slotted antennas. Manufacture strategy, based on additive manufacturing techniques, will also be discussed.
