Professor Justin Wark: Publications

Investigation of femtosecond collisional ionization rates in a solid-density aluminium plasma.

Nature communications 6 (2015) 6397-6397

Authors:

SM Vinko, O Ciricosta, TR Preston, DS Rackstraw, CRD Brown, T Burian, J Chalupský, BI Cho, H-K Chung, K Engelhorn, RW Falcone, R Fiokovinini, V Hájková, PA Heimann, L Juha, HJ Lee, RW Lee, M Messerschmidt, B Nagler, W Schlotter, JJ Turner, L Vysin, U Zastrau, JS Wark

Abstract:

The rate at which atoms and ions within a plasma are further ionized by collisions with the free electrons is a fundamental parameter that dictates the dynamics of plasma systems at intermediate and high densities. While collision rates are well known experimentally in a few dilute systems, similar measurements for nonideal plasmas at densities approaching or exceeding those of solids remain elusive. Here we describe a spectroscopic method to study collision rates in solid-density aluminium plasmas created and diagnosed using the Linac Coherent light Source free-electron X-ray laser, tuned to specific interaction pathways around the absorption edges of ionic charge states. We estimate the rate of collisional ionization in solid-density aluminium plasmas at temperatures ~30 eV to be several times higher than that predicted by standard semiempirical models.

The creation of large-volume, gradient-free warm dense matter with an x-ray free-electron laser

Physics of Plasmas AIP Publishing 22:3 (2015) 030703

Authors:

A Lévy, P Audebert, R Shepherd, J Dunn, M Cammarata, O Ciricosta, F Deneuville, F Dorchies, M Fajardo, C Fourment, D Fritz, J Fuchs, J Gaudin, M Gauthier, A Graf, HJ Lee, H Lemke, B Nagler, J Park, O Peyrusse, AB Steel, SM Vinko, JS Wark, GO Williams, D Zhu, RW Lee

Simulations of x-ray diffraction from uniaxially-compressed highly-textured polycrystalline targets

(2015)

Authors:

David McGonegle, Despina Milathianaki, Bruce A Remington, Justin S Wark, Andrew Higginbotham

Saturable Absorption of an X-Ray Free-Electron-Laser Heated Solid-Density Aluminum Plasma

Physical Review Letters American Physical Society (APS) 114:1 (2015) 015003

Authors:

DS Rackstraw, O Ciricosta, SM Vinko, B Barbrel, T Burian, J Chalupský, BI Cho, H-K Chung, GL Dakovski, K Engelhorn, V Hájková, P Heimann, M Holmes, L Juha, J Krzywinski, RW Lee, S Toleikis, JJ Turner, U Zastrau, JS Wark

The creation of large-volume, gradient-free warm dense matter with an x-ray free-electron laser

Physics of Plasmas 22:3 (2015)

Authors:

Abstract:

The efficiency and uniformity of heating induced by hard x-ray free-electron laser pulse is investigated for 0.5 μm silver foils using the X-ray Pump Probe instrument at the Linac Coherent Light Source facility. Intense 8.9 keV x-ray pulses of 60fs duration deposit energy predominantly via inner-shell ionization to create a non-equilibrium Ag solid density plasma. The x-ray pulses are focused to 14 × 17 μm² by means of beryllium lenses and by varying the total beam energy, the energy deposition is varied over a range of irradiances from 4.4 to 6.5 × 10¹⁵ ∼ W/cm². Two time-and-space resolved interferometers simultaneously probed the expansion of the front and rear sample surfaces and find evidence of a nearly symmetric expansion pointing to the uniformity of energy deposition over the full target thickness. The experimental results are compared with two different hydrodynamic simulations of the sample expansion. The agreement between experimental and theoretical results yields an estimate of the temperature evolution as a function of x-ray irradiance that varies from 8 to 10 eV for the x-ray irradiances studied.

51��