Observation of annular electron beam transport in multi-TeraWatt laser-solid interactions

Electron energy transport experiments conducted on the Vulcan 100 TW laser facility with large area foil targets are described. For plastic targets it is shown, by the plasma expansion observed in shadowgrams taken after the interaction, that there is a transition between the collimated electron flow previously reported at the 10 TW power level to an annular electron flow pattern with a 20 degrees divergence angle for peak powers of 68 TW. Intermediate powers show that both the central collimated flow pattern and the surrounding annular-shaped heated region can co-exist. The measurements are consistent with the Davies rigid beam model for fast electron flow (Davies 2003 Phys. Rev. E 68 056404) and LSP modelling provides additional insight into the observed results.

Transport Properties Investigation of Aqueous Protic Ionic Liquid Solutions through Conductivity, Viscosity, and NMR Self-Diffusion Measurements

We present a study on the transport properties through conductivity (s), viscosity (?), and self-diffusion coefficient (D) measurements of two pure protic ionic liquids—pyrrolidinium hydrogen sulfate, [Pyrr][HSO4], and pyrrolidinium trifluoroacetate, [Pyrr][CF3COO]—and their mixtures with water over the whole composition range at 298.15 K and atmospheric pressure. Based on these experimental results, transport mobilities of ions have been then investigated in each case through the Stokes–Einstein equation. From this, the proton conduction in these PILs follows a combination of Grotthuss and vehicle-type mechanisms, which depends also on the water composition in solution. In each case, the displacement of the NMR peak attributed to the labile proton on the pyrrolidinium cation with the PILs concentration in aqueous solution indicates that this proton is located between the cation and the anion for a water weight fraction lower than 8%. In other words, for such compositions, it appears that this labile proton is not solvated by water molecules. However, for higher water content, the labile protons are in solution as H3O+. This water weight fraction appears to be the solvation limit of the H+ ions by water molecules in these two PILs solutions. However, [Pyrr][HSO4] and [Pyrr][CF3COO] PILs present opposed comportment in aqueous solution. In the case of [Pyrr][CF3COO], ?, s, D, and the attractive potential, Epot, between ions indicate clearly that the diffusion of each ion is similar. In other words, these ions are tightly bound together as ion pairs, reflecting in fact the importance of the hydrophobicity of the trifluoroacetate anion, whereas, in the case of the [Pyrr][HSO4], the strong H-bond between the HSO4– anion and water promotes a drastic change in the viscosity of the aqueous solution, as well as on the conductivity which is up to 187 mS·cm–1 for water weight fraction close to 60% at 298 K.

Role of charge in the radioprotection of E. coli by thiols.

The role of net charge (Z) of thiols in their ability to radioprotect cells has been investigated in a glutathione (GSH)-deficient strain of E. coli. This strain, 7, is deficient in the enzyme gamma-glutamylcysteine synthetase and allows the effects of added low molecular weight thiols to be studied. Using the gas explosion system it is possible to measure the chemical repair of the free-radical precursors of lethal lesions by thiols in intact cells. The first-order chemical repair rate in strain 7 is 280s(-1) in comparison with 1100s(-1) in the wild-type strain 1157. From the measured difference in the intracellular concentration of GSH between the wild-type and the mutant, this gives a second-order repair rate, k(r)'s of 1.23 +/- 0.3 X 10(5) dm(3)mol(-1)s(-1). Measurement of intracellular thiol levels after addition of various low molecular weight thiols showed that uptake was rapid, leading to stable thiol levels within 1 min. The ratios of the intracellular to extracellular concentrations (C-in/C-out) were 0.74 for 3-mercaptopropionic acid (Z=-1), 0.56 for 2-mercaptoethanol (Z=0), 1.47 for cysteamine (Z=+1) and 1.04 for WR1065 (Z=+2). The k(r)'s for these thiols were 1.3 +/- 0.5 X 10(5) dm(3)mol(-1)s(-1) for 30-mercaptopropionic acid, 3.3 +/- 1.6 x 10(5) dm(3)mol(-1)s(-1) for 2-mercaptoethanol, 3.9 +/- 1.1 X 10(5) dm(3)mol(-1)s(-1) for cysteamine and 2.7 +/- 1.1 X 10(6) dm(3)mol(-1)s(-1) for WR1065. These are lower and increase less with charge than previously published values for chemical repair in isolated pBR322 DNA, probably because of the association of nucleoproteins and polyamines with the cellular DNA of E. coli. However, the approximate three-fold increase in k(r) per unit increase in Z shows that the counter-ion condensation and co-ion depletion are important in determining the effectiveness of charged thiols in the radioprotection of E. coli.

Dynamics of charge-displacement channeling in intense laser-plasma interactions

The dynamics of transient electric fields generated by the interaction of high intensity laser pulses with underdense plasmas has been studied experimentally with the proton projection imaging technique. The formation of a charged channel, the propagation of its front edge and the late electric field evolution have been characterized with high temporal and spatial resolution. Particle-in-cell simulations and an electrostatic, ponderomotive model reproduce the experimental features and trace them back to the ponderomotive expulsion of electrons and the subsequent ion acceleration.

Comparison of plasma transport theory with measurements in a H- discharge

This paper and its companion paper describe the comparison between a one-dimensional theoretical model of a hydrogen discharge in a magnetic multipole plasma source and experimental measurements of the plasma parameters. The discharge chamber, described here, has been designed to produce significant densities of H- ions by incorporating a weak transverse field through the discharge to obtain electron cooling so as to maximize H- production. Langmuir probes are used to monitor the plasma, determining the ion density, the electron density and temperature and the plasma potential. The negative density is measured by photo-detachment of the extra electron using an intense laser beam. The model, described in the companion paper, uses the presented source geometry to calculate these plasma quantities as a function of the major are parameters; namely the are current and voltage and gas pressure. Good agreement is obtained between theory and experiment as a function of position and arc parameters.