Derivation of the static structure factor in strongly coupled non-equilibrium plasmas for X-ray scattering studies

Gregori, G.; Ravasio, A.; Höll, A.; Glenzer, S. H.; Rose, S. J.

doi:10.1016/j.hedp.2007.02.006

Cited by 68 publications

(71 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Calculations of S Rayl ðkÞ with more sophisticated models for the ion-ion structure factor [22,25] ion-temperature scaling derived within the Debye-Hückel model.…”

Section: Prl 108 217402 (2012) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Ultrafast Transitions from Solid to Liquid and Plasma States of Graphite Induced by X-Ray Free-Electron Laser Pulses

et al. 2012

View full text Add to dashboard Cite

We used photon pulses from an x-ray free-electron laser to study ultrafast x-ray-induced transitions of graphite from solid to liquid and plasma states. This was accomplished by isochoric heating of graphite samples and simultaneous probing via Bragg and diffuse scattering at high time resolution. We observe that disintegration of the crystal lattice and ion heating of up to 5 eV occur within tens of femtoseconds. The threshold fluence for Bragg-peak degradation is smaller and the ion-heating rate is faster than current x-ray-matter interaction models predict. [2,3], and in high-energy-density science [4]. Triggered by intense photon pulses in the laboratory, such phase transitions are complex. The kinetics of optical photoninduced transitions has been studied extensively [1,5,6]. Optical photons are absorbed through collective electronic processes [7]. In contrast, x-ray-induced dynamics are expected to differ substantially because x rays generate high-energy photoelectrons that equilibrate through collisional ionization and develop into a hot electron gas. Additionally, x rays penetrate materials to depths of more than 1 m, whereas optical penetration depths are rather short ($ 10 nm). The emergence of x-ray free-electron lasers (XFELs) now enables the study of ultrafast x-rayinduced transitions at extremely high time resolution and over a large, isochorically heated volume.We used pulses from an XFEL to excite graphite isochorically to extreme conditions with electron temperatures up to about 10 eV [8]. This induced ultrafast electronic processes and, ultimately, an order-disorder transformation. We characterized the x-ray-induced ultrafast ionization, lattice destruction, and temperaturerelaxation dynamics with a temporal resolution of tens of femtoseconds by measuring the dynamic structure factor, Sðk; !Þ, simultaneously both on and off the Bragg resonance. At low x-ray intensities, the crystal structure stays intact, the Bragg peak is very strong, and diffuse scattering is weak. With increasing intensities, the Bragg peak degrades due to atomic ionization and motion, and the forward diffuse elastic-scattering signal increases correspondingly. The combined measurements of the pulse-width dependence and fluence dependence of these signals allowed us to extract the ion temperature as a function of time.We performed the experiments at the Linac Coherent Light Source (LCLS) [9], using an x-ray energy of 2 keV, pulse energies of up to 2.8 mJ, and pulse durations of 40, 60, and 80 fs. We determined the multiple-shot averaged x-ray pulse duration from statistical analysis of single-shot spectra within an error of 30% [10]. The pulse energy was measured for each shot using an upstream nitrogenfluorescence detector [11]. The transmission of the beam line was about ð15 AE 3Þ% [12]. The focal spot area was determined from microscopic analysis of low-fluence beam imprints in yttrium aluminum garnet [13]. We focused the x-ray pulses to a beam area of 36-10 m 2 onto a highly oriented pyrolytic-graphite (HOPG) crystal, a...

show abstract

“…Calculations of S Rayl ðkÞ with more sophisticated models for the ion-ion structure factor [22,25] ion-temperature scaling derived within the Debye-Hückel model.…”

Section: Prl 108 217402 (2012) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Ultrafast Transitions from Solid to Liquid and Plasma States of Graphite Induced by X-Ray Free-Electron Laser Pulses

et al. 2012

View full text Add to dashboard Cite

show abstract

“…[7] and [9], respectively. In addition, the screening function q(k) was calculated within classical linear response [46,47] …”

Section: Application To X-ray Scattering a Description Of The Scmentioning

confidence: 99%

Structure of strongly coupled multicomponent plasmas

et al. 2008

View full text Add to dashboard Cite

We investigate the short range structure in strongly coupled, fluid-like plasmas using the hypernetted chain approach generalized to multi-component systems. Good agreement with numerical simulations validates this method for the parameters considered. We found strong mutual impact on the spacial arrangement for systems with multiple ion species which were most clearly pronounced in the static structure factor. Quantum pseudo-potentials were used to mimic diffraction and exchange effects in dense electron-ion systems. We demonstrate that the different kinds of pseudo-potentials proposed lead to large differences in both the pair distributions and the structure factors. Large discrepancies were also found in the predicted ion feature of the x-ray scattering signal illustrating the need for comparison with full quantum calculations or experimental verification.

show abstract

“…The scattered spectrum has a strong Rayleigh peak around 2960 eV and a Comptondownshifted feature. Scattered x-ray spectra were calculated using the x-ray scattering (XRS) code, which uses the finite-temperature random-phase approximation with static local field corrections to obtain the spectral shape of the inelastic (Compton) feature caused by scattering from free electrons [25]. The elastic scattering intensity strongly depends on the degree of ion-ion correlations in the plasma via the structure factor S ii [20].…”

mentioning

confidence: 99%