Investigation of Al plasmas from thin foils irradiated by high-intensity extreme ultraviolet

Dynamics and spectral transmission of Al plasma produced by extreme ultraviolet(EUV)irradiation of 0.75-mm thick Al foil is investigated.The EUV radiation with the peak power density in the range of 0.19-0.54 TW/cm 2 is provided by Z-pinch formed by W multiwire array implosion in the Angara-5-1 facility.Geometry of the experiment ensures that there are no plasma fluxes from the pinch toward the Al foil and plasma.The same EUV source is used as a back illuminator for obtaining the absorption spectrum of Al plasma in the wavelength range of 5e24 nm.It comprises absorption lines of ions Al^(4+),Al^(5+),Al^(6+),Al^(7+).Analysis of relative intensities of the lines shows that those ions are formed in dense Al plasma with a temperature of~20 eV.Dynamics of Al plasma has been investigated with transverse laser probing.We have also performed radiation-gas-dynamics simulations of plasma dynamics affected by external radiation,which includes self-consistent radiation transport in a plasma shell.The simulations show good agreement with an experimental absorption spectrum and with experimental data concerning plasma dynamics,as well as with the analysis of line absorption spectrum.This confirms the correctness of the physical model underlying these simulations.

Metrology for sub-Rayleigh-length target positioning in~10^(22)W/cm^(2)laser-plasma experiments

Tight focusing with very small f-numbers is necessary to achieve the highest at-focus irradiances.However,tight focusing imposes strong demands on precise target positioning in-focus to achieve the highest on-target irradiance We describe several near-infrared,visible,ultraviolet and soft and hard X-ray diagnostics employed in a~10^(22)W/cm^(2)laser±plasma experiment.We used nearly 10 J total energy femtosecond laser pulses focused into an approximately1.3-μm focal spot on 5±20μm thick stainless-steel targets.We discuss the applicability of these diagnostics to determine the best in-focus target position with approximately 5μm accuracy(i.e.,around half of the short Rayleigh length)and show that several diagnostics(in particular,3ωreflection and on-axis hard X-rays)can ensure this accuracy.We demonstrated target positioning within several micrometers from the focus,ensuring over 80%of the ideal peak laser intensity on-target.Our approach is relatively fast(it requires 10±20 laser shots)and does not rely on the coincidence of low-power and high-power focal planes.

Radial density profile and stability of capillary discharge plasma waveguides of lengths up to 40 cm

We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650µm to 2 mm and lengths of 9 to 40 cm.To the best of the authors’knowledge,40 cm is the longest discharge capillary plasma waveguide to date.This length is important for≥10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage.Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible to<0.2%and their average on-axis plasma electron density to<1%.These variations explain only a small fraction of laser-driven plasma wakefield acceleration electron bunch variations observed in experiments to date.Measurements of laser pulse centroid oscillations revealed that the radial channel profile rises faster than parabolic and is in excellent agreement with magnetohydrodynamic simulation results.We show that the effects of non-parabolic contributions on Gaussian pulse propagation were negligible when the pulse was approximately matched to the channel.However,they affected pulse propagation for a non-matched configuration in which the waveguide was used as a plasma telescope to change the focused laser pulse spot size.