Modeling space-resolved ion dynamics in ECR plasmas for predicting in-plasma β-decay rates

Abstract

Lifetimes of radioactive nuclei are known to be affected by the level configurations of their respective atomic shells. Immersing such isotopes in environments composed of energetic charged particles such as stellar plasmas can result in β-decay rates orders of magnitude different from those measured terrestrially. Accurate knowledge of the relation between plasma parameters and nuclear decay rates are essential for reducing uncertainties in present nucleosynthesis models, and this is precisely the aim of the PANDORA experiment. Currently, experimental evidence is available for fully stripped ions in storage rings alone, but the full effect of a charge state distribution (CSD) as exists in plasmas is only modeled theoretically. PANDORA aims to be the first to verify these models by measuring the β-decay rates of select isotopes embedded in electron cyclotron resonance (ECR) plasmas. For this purpose, it is necessary to consider the spatial inhomogeneity and anisotropy of plasma ion properties as well as the non-local thermodynamic equilibrium (NLTE) nature of the system. We present here a 3D ion dynamics model combining a quasi-stationary particle-in-cell (PIC) code to track the motion of macroparticles in a pre-simulated electron cloud while simultaneously using a Monte Carlo (MC) routine to check for relevant reactions describing the ion population kinetics. The simulation scheme is robust, comprehensive, makes few assumptions about the state of the plasma, and can be extended to include more detailed physics. We describe the first results on the 3D variation of CSD of ions both confined and lost from the ECR trap, as obtained from the application of the method to light nuclei. The work culminates in some perspectives and outlooks on code optimization, with a potential to be a powerful tool not only in the application of ECR plasmas but for fundamental studies of the device itself.

Experimental and numerical investigation of magneto-plasma optical properties toward measurements of opacity relevant for compact binary objects

“…To conclude, the numerical investigation has highlighted peculiar modification of plasma opacity led by a structured ECR plasma, providing numerical predictions of the latter, accordingly to the atomic database on argon transitions, which could support future experimental measurements in gaseous plasmas. Further investigations, extending the method by giving additional inputs to FLYCHK for more precise calculations, for example, the ECR charge state distribution expected for metallic/gaseous plasmas, which numerical study is under development (Mishra et al, 2020), will produce outputs more tight to real scenarios achievable with experiments. Thus, having access to layered optical properties of the plasma would help in deconvolving the stratified emission, otherwise only partially decoded by the inverse problem techniques, and still suffering from residual large uncertainties.…”

Metallic Neutral Vapours Diffusion in Electron Cyclotron Resonance Ion Sources: Fluid Dynamics and Particle Tracing Simulations

“…To provide deeper insights on the ECR plasma dynamics effects to the atom-to-ion conversion, a Monte Carlo (MC) routine was developed in MATLAB, based on the data retrieved from self-consistent (SC) plasma simulations of electron dynamics in the PANDORA plasma trap [11,8,12]. Plasma trap parameters for the SC simulations are in Table 1, and further details can be found in [8].…”

“…SC simulations provided 3D electron density and energy density maps, later used to compute dominant collisional processes reaction rates in the metal atom dynamics: electron-impact ionization (EI) and charge-exchange (CEX). Because of typical in-homogeneous and anisotropic plasma parameters, this resulted in space-dependent reaction rate maps [12], which are inversely related to the EI and CEX cross-sections, σ EI and σ CEX , respectively. The cross-section σ EI was computed according to the general formalism of Lotz [13], while σ CEX was computed according to the standard Müller-Salzborn formula [14].…”

A new approach to β-decays studies impacting nuclear physics and astrophysics: The PANDORA setup

“…Taking into account the HPGe array detection efficiency, to reach a 3-sigma confidence level the experimental run should last from about one day up to about three months depending on the physics case investigated and the lifetime variation observed [13]. Numerical simulations [26,27] are now ongoing to estimate the expected density and temperature distribution in PANDORA, and then to perform a kind of "virtual experiment" addressing and supporting the data taking that will start at the end of 2024.…”