Effects of the electron energy distribution function on modeled x-ray spectra

Abstract

This paper presents the results of a broad investigation into the effects of the electron energy distribution function on the predictions of nonlocal thermodynamic equilibrium collisional-radiative atomic kinetics models. The effects of non-Maxwellian and suprathermal ("hot") electron distributions on collisional rates (including three-body recombination) are studied. It is shown that most collisional rates are fairly insensitive to the functional form and the characteristic (central or average) energy of the electron distribution function as long as the characteristic energy is larger than the threshold energy for the collisional process. Collisional excitation and ionization rates are, however, highly sensitive to the number of hot electrons. This permits the development of robust spectroscopic diagnostics that can be used to characterize the electron density, bulk electron temperature, and hot electron fraction of plasmas with nonequilibrium electron distribution functions. Hot electrons are shown to increase and spread out plasma charge state distributions, amplify the intensities of emission lines fed by direct collisional excitation and radiative cascades, and alter the structure of satellite features in both K - and L -shell spectra. The characteristic energy, functional form, and spatial properties of hot electron distributions in plasmas are open to characterization through their effects on high-energy continuum and line emission and on the polarization of spectral lines.

Effects of the Electron Energy Distribution Function on Line and Continuum Emission

“…Although hot electrons in this distribution have effects on Ti ionization balances and line emission that are very similar to the effects of the 10 keV Gaussian distribution used in Fig. 3, the highenergy bremsstrahlung emission of such a narrow beam would be very different than that of the Maxwellian, as high-energy bremsstrahlung emission tends to mimic the functional form of the hot electron distribution [11]. Figure 6 shows that the absolute amplitude of the K-shell line emission is much larger in the presence of hot electrons.…”

“…Combinations of these forms can reproduce a wide range of non-equilibrium EDF behavior. These distributions are discussed in detail in [11]. Although a wide range of characteristic energies and functional forms of the hot electron distribution are commonly used (chosen to reflect properties of hot electron characteristics in a variety of plasmas), it turns out that many important collisional rates are fairly insensitive to the functional form of the electron distribution and ε H as long as ε H is larger than the transition energy ∆E of the collisional processes.…”

“…De-excitation and recombination processes are therefore fairly insensitive to the precise functional form and energy of the hot electron distribution. Details of the integration and the EDF dependence of non-resonant collisional excitation, deexcitation, and three-body and radiative recombination processes are given in [11]. …”

Study of x-rays produced from debris-free sources with Ar, Kr and Kr/Ar mixture linear gas jets irradiated by UNR Leopard laser beam with fs and ns pulse duration

“…Voigt line profiles are used to construct the spectra in order to take into account the effects of Doppler broadening and natural broadenings in the plasma, as well as instrumental broadening due to limited resolution of the detector. Synthetic spectra can be generated from each model dependent on plasma parameters such as electron temperature, electron density (ne), and parameters of the non-Maxwellian distribution function to include hot electrons (see, for example, [24]). …”

The importance of EBIT data for Z-pinch plasma diagnostics

“…The experim ental Al/ W X-pinch spectrum is shown at the top of transitions in L-shell M o, the lines N3 a nd N4 could not be a ssigned to particular peaks in this X-pinch spectrum. Figure 8 shows the M-shell W modeling of the above mentioned combined X-pinch spectra at an electron tem perature Te=1 keV, electron density Ne= 10 21 cm -3 , and a sm all portion of non-Maxw ellian electrons f= 0.03 (for more about the influence of hot electrons on x-ray spectra, see, for example, [25][26]). …”