Atomic kinetics for isochoric heating of solid aluminum under short intense XUV free electron laser irradiation

High Energy Density Physics

2016

Collisional-radiative models enable average ionization and ionization populations, plus the rates of absorption and emission of radiation to be calculated for plasmas not in thermal equilbrium. At high densities and low temperatures, electrons may have a high occupancy of the free electron quantum states and evaluations of rate coefficients need to take into account the free electron degeneracy. We demonstrate that electron degeneracy can reduce collisional rate coefficients by orders-of-magnitude from values calculated neglecting degeneracy. We show that assumptions regarding the collisional differential cross-section can alter collisional ionization and recombination rate coefficients by a further factor two under conditions relevant to inertial fusion.

Section: Introductionmentioning

confidence: 99%

“…ionization energy is negative on our free electron energy scale, hence our assumed positive E ion has the opposite sign to the free electron kinetic energy E in equation (9). The value of E ion should include a calculation of the 110 continuum lowering effect [20].…”

mentioning

confidence: 99%

Free electron degeneracy effects on collisional excitation, ionization, de-excitation and three-body recombination

High Energy Density Physics

2016

“…The early temperatures differ due to the differences in heat capacity between the two models, which converge as the temperature rises; the difference in final temperature is due to different overall absorption coefficients. The discrepancy in temperature between the two models is lower in the case of covalently bonded carbon, modeled initially as neutral, compared to studies of metallically bonded aluminum [13,14], which begins with an established large density of valence electrons. We have neglected any heating of the ions, as the time scale for this is significantly longer than the present simulation.…”

Section: Effects On Macroscopic Propertiesmentioning

confidence: 71%

“…Such approaches are approximate and valid only at low electron density and high temperature as they neglect degeneracy effects due to the Pauli exclusion principle which states that a maximum of one electron can occupy a quantum state [12]. A plasma ionization calculation where the degeneracy of free electrons is considered has shown significant degeneracy effects can be expected for experiments using extreme ultraviolet free electron laser irradiation of solid aluminum targets [13,14].…”

Section: Introductionmentioning

confidence: 99%

Ionization rate coefficients in warm dense plasmas

Aslanyan

2015

Phys. Rev. E

We recast the atomic processes in a warm, dense plasma using Fermi-Dirac statistics and compare them to the rates of the usual Maxwell-Boltzmann approach of many collisional-radiative models. Population calculations show insignificant differences to calculations assuming nondegenerate free electrons of plasmas at solid density close to local thermodynamic equilibrium, but show departures in average ionization in the presence of strong photoionization. For example, we show that electron degeneracy affects the evolution of plasmas created by ultraviolet free electron laser interaction with solid targets.

“…Re-cent advances in short wavelength lasers have allowed the creation of warm dense plasmas at solid or greater densities, due to their correspondingly high critical densities. These advances have spurred investigations into the effects of degeneracy on the atomic rates and hence on macroscopic plasma properties [1,2,3].…”

Section: Introductionmentioning

confidence: 99%

Efficient calculation of degenerate atomic rates by numerical quadrature on GPUs

Aslanyan

Computer Physics Communications

2017

The rates of atomic processes in cold, dense plasmas are governed strongly by effects of quantum degeneracy. The electrons follow Fermi-Dirac statistics and their high density limits the number of quantum states available for occupation after a collision. These factors preclude a direct solution to the usual rate coefficient integrals. We summarise the formulation of this problem and present a simple, but efficient method of evaluating collisional rate coefficients via direct numerical integration. Numerical quadrature has an intrinsically high level of parallelism, ideally suited for graphics processor units. GPUs are particularly suited to this problem because of the large number of integrals which must be carried out simultaneously for a given atomic model. A CUDA code to calculate the rates of significant atomic processes as part of a collisional-radiative model is presented and discussed. This approach may be readily extended to other applications where rapid and repeated evaluation of many integrals is required.