Ultrafast nonequilibrium ion and electron dynamics of a neon plasma produced by an ultra-intense x-ray pulse

Theoretical exploration of the population dynamics at fine-structure levels of Ar atoms interacting with ultrafast ultraintense x-ray free electron laser (XFEL) pulses is conducted. A time-dependent rate equation based on a detailed-level accounting approach is applied for tracking population levels, encompassing microscopic atomic processes such as photoexcitation, radiative decay, photoionization and Auger decay. A Monte Carlo algorithm is implemented to solve large-scale rate equations efficiently. The primary investigation centers on generating Ar17+ through resonant absorption by the second-harmonic radiation of the x-ray pulse. The calculated population ratios of Ar17+ to Ar16+ align well with the experimental measurements (LaForge et al 2021 Phys. Rev. Lett. 127 213202). In comparison to the transition energy of the strongest line, ( 1 s 2 ) 0 → ( 1 s 1 / 2 2 p 3 / 2 ) 1 of Ar16+, there is a distinct ∼25 eV red shift in the peak ratio, which is attributed to the presence of intricate resonant channels in the lower ionization stages. The results demonstrate the sensitivity of the population ratio Ar17+/Ar16+ to the laser pulse parameters such as x-ray pulse duration, bandwidth and the contribution of second-harmonic radiation, indicating their potential as diagnostic tools in future experiments.

Section: Resultsmentioning

confidence: 99%

Evolution of level population in Ar interacting with XFEL pulses: impact of resonant absorptions

Yan,

Jin

et al. 2024

“…We previously investigated the population kinetics in the interaction of XFEL with Ne by directly solving a TDRE [27,28,32,[35][36][37]. In the present work, we developed a Monte Carlo method to solve the TDRE to study the population kinetics of Ar atoms interacting with XFEL.…”

Section: Time-dependent Rate Equation: a Monte Carlo Methodsmentioning

confidence: 99%

Effects of single-photon double photoionization and direct double Auger decay on K-shell ionization kinetics of Ar atoms interacting with XFEL pulses

Li¹,

Gao²,

Zeng³

et al. 2022

Self Cite

In studies investigating the interaction of matter with ultraintense, ultrashort Xray free electron laser (XFEL) pulses, the evolution kinetics are generally described by directly solving a time-dependent rate equation that considers single-photon and single-electron processes. In the present study, we show the eﬀects of single-photon double photionization and direct double Auger decay in the K-shell ionization kinetics of XFELs interaction with argon atoms. Because a huge number of coupled transition channels are present in the K-shell ionization, we develop a Monte Carlo method to simulate the complex ionization kinetic processes and give the level population evolution of ions and charge state distribution (CSD). The K-shelldominated ionization dynamics of Ar irradiated by XFEL pulses with photon energies of 5000, 5500 and 6500 eV are investigated and compared with available experimental observations of the CSD. The results show that the population fractions of Ar5+, Ar6+ and Ar9+ are increased by 78%, 152% and 144%, respectively, by these higher-order processes at a photon energy of 5000 eV. Including the direct double-electron processes, the predicted CSDs are in better agreement with the experiments carried out at the photon energies of 5000, 5500 and 6500 eV. It is expected that the developed theoretical formalism can be used to more accurately calibrate the beam proﬁle and intensity of XFELs.

“…For some NLTE plasmas, the Fokker-Planck approach can be used when the electron energy distribution is beyond Maxwellian [40][41][42][43]:…”

Section: Reaction Ratesmentioning

confidence: 99%

Monte Carlo method for investigating population kinetics in non-local thermodynamic equilibrium plasmas

Tao

Zhou

Zhang

et al. 2023

We propose a new method to solve the collisional-radiative model with the Monte Carlo method for investigating population kinetics of non-local thermodynamic equilibrium plasmas. The collisional-radiative model is solved using massive sample particles accounting detailed energy levels.Whether an atom/ion undergoes an ionization/excitation/decay process is determined by probabilities calculated from ionization cross-sections, excitation and decay rates. By continuously iterating this process for massive atoms/ions, the ionization population distribution is obtained. The numerical convergence can be achieved for a mid-Z element using 10^3 particles in the Monte Carlo simulation. The results of the Monte Carlo simulations are compared with other methods and experimental results. The self emission spectra of silicon plasma is obtained and the ionization population distribution of silicon and iron plasmas are calculated. The proposed method can be used to interpret high energy density experiments and astrophysical phenomena where non-local thermodynamic equilibrium effects play vital roles.