Ion acceleration by superintense laser pulses in plasmas

Ion acceleration by petawatt laser radiation in underdense and overdense plasmas is studied with 2D3V-PIC (Particle in Cell) numerical simulations. These simulations show that the laser pulse drills a channel through the plasma slab, and electrons and ions expand in vacuum. Fast electrons escape first from the electron-ion cloud. Later, ions gain a high energy on account of the Coulomb explosion of the cloud and the inductive electric field which appears due to fast change of the magnetic field generated by the laser pulse. Similarly, when a superintense laser pulse interacts with a thin slab of overdense plasma, its ponderomotive pressure blows all the electrons away from a finite-diameter spot on the slab. Then, due to the Coulomb explosion, ions gain an energy as high as 1 GeV. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 80–86 (25 July 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Spectroscopic and Thermal Studies on 2,4,6-trinitro Toluene (TNT)

The kinetics and mechanism of the initial stage of thermal decomposition of 2,4,6-trinitro toluene (TNT), a widely used high explosive, have been studied, together with its morphology and evolved gaseous products using thermogravimetry (TG), differential thermal analysis (DTA), infrared spectroscopy (IR) and hot-stage microscopy. The kinetics of the thermolysis has been followed by IR after suppressing volatilisation by matrixing and by isothermal TG without suppressing volatilisation to simulate actual user conditions. The best linearity was obtained for Avrami-Erofeev equation for n=1 in isothermal IR and also in isothermal TG. The activation energy was found to be 135 kJ mol⁻¹, with logA (in s⁻¹) 12.5 by IR. The effect of additives on the initial thermolysis of TNT has also been studied. Evolved gas analysis by IR showed that CO₂, NO₂, NO and H₂O are more dominant than N₂O, HCN and CO. The decomposition involves the initial rupture of the C-NO₂ bond, weakened by hydrogen bonding with the labile hydrogen atom of the adjacent CH₃ group, followed by the abstraction of the hydrogen atom of the methyl group by NO₂, generated in the initial step. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and magnetic characterization of CoMoN<Subscript>2</Subscript> nanoparticles

A new ternary nitride, CoMoN₂, was prepared in the nanosize regime of 9.0 ± 2.0 nm, by nitridation of the precursor intermetallic nitride Co₃Mo₃N. XRD–Rietveld analysis revealed the presence of 0.60 (±0.02) mass % of Co impurity phase. The calculated space groups of CoMoN₂ and Co are P6 ₃ /mmc and Fm-3m, respectively. The N atoms lie at the interstitial sites and the 12 calculated nitrogen sites indicate the presence of a layered structure. The XPS studies indicated the presence of the nitride and surface oxynitride/oxide phases. CoMoN₂ is an interstitial nitride with Co and Mo in the zero oxidation state. The room temperature susceptibility is estimated after subtracting the ferromagnetic contribution from cobalt and found to be 2.7 × 10⁻⁴ emu g⁻¹ Oe⁻¹, indicating the Pauli-paramagnetic nature. The ferromagnetic exchange interactions between the Co atoms in CoMoN₂ are reduced due to the presence of Mo and N in the crystal lattice. The hysteresis loop shift 19 Oe is attributed to the demagnetizing dipolar fields created in the soft CoMoN₂ phase by the hard Co phase.     

Mössbauer and calorimetric studies of portland cement hydration in the presence of black gram pulse

Effect of different concentrations of naturally occurring admixture in the form of fine powder of black gram pulse (BGP) on the hydration of Portland cement was studied by isothermal calorimetry and ⁵⁷Fe Mössbauer spectroscopy. The spectra were recorded for anhydrous cement and the hydration products at room temperature and 77 K. In the presence of BGP, the spectra showed superparamagnetic doublets at room temperature and the sextet at 77 K, due to the presence of fine particles of iron containing component. Mössbauer studies of hydration products confirmed the formation of nanosize hydration products containing Fe^3?+?. The isomer shift (δ) and the quadrupole splitting (ΔE _Q) values of C₄AF in the cement confirmed iron in an octahedral and tetrahedral environment with +3 oxidation state. The high value of quadrupole splitting showed the high asymmetry of the electron environment around the iron atom. The overall mechanism of the hydration of cement in presence of BGP is discussed.     

Effect of nickel nanofillers on the dielectric and magnetic properties of composites based on rubber in the X-band

Nickel–rubber nanocomposites were synthesized by incorporating ferromagnetic nickel nanoparticles in a natural rubber as well as neoprene rubber matrix. Complex dielectric permittivity and magnetic permeability of these composites were evaluated in the X-band microwave frequencies at room temperature using cavity perturbation technique. The dielectric loss in natural rubber is smaller compared to neoprene rubber. A steady increase in the dielectric permittivity is observed with increase in the content of nickel in both the composites. The magnetic permeability exhibits a steady decrease with increase in frequency and magnetic loss shows a relaxation at 8 GHz. The suitability of these composites as microwave absorbers is modeled based on the reflection loss which is dependant on the real and imaginary components of the complex dielectric permittivity and magnetic permeability.     

Quasi-static electromagnetic pulse generated by ultra-intense laser pulses

A solitary structure of quasi-static electromagnetic pulse is formed in moderate density plasmas by a propagation of ultra-intense and ultra-short laser pulse, which is formed after the laser pulse is depleted and slowly propagates in the laser propagation direction. The structure is sustained by huge magnetic pressure and compensating electric field which are in an electromagnetic equilibrium together with the plasma motion. The solitary structure is formed when the resonance condition is satisfied and laser intensity is high enough to induce huge magnetic field pressure.     

Inner-shell ionization of rotating linear molecules in the presence of spin-dependent interactions: Entanglement between a photoelectron and an auger electron

The complex dynamical behavior of the electron sheath in laser driven ion acceleration leads to variations in ion beam pointing and ion energy modulation. These processes are derived from high resolution particle spectroscopy and 2D-PIC simulations. The phenomena arise from ion source movement if laser irradiation occurs at oblique incidence. Different laser absorption processes act in dependence on laser parameter which determines the ion acceleration.     

Characterization of heat-wave propagation through laser-driven Ti-doped underdense plasma

The propagation of a laser-driven heat-wave into a Ti-doped aerogel target was investigated. The temporal evolution of the electron temperature was derived by means of Ti K-shell X-ray spectroscopy, and compared with two-dimensional radiation hydrodynamic simulations. Reasonable agreement was obtained in the early stage of the heat-wave propagation. In the later phase, laser absorption, the propagation of the heat-wave, and hydrodynamic motion interact in a complex manner, and the plasma is mostly re-heated by collision and stagnation at the target central axis.     

Shock velocity measurements using microwave Doppler shift

A commercially available 10.587 GHz microwave Doppler module is used for the measurement of shock velocity in a conventional shock tube. With proper electronic circuits the Doppler frequency obtained is found to be quite noisefree and consistent for shock velocities in the range of 1.8 mm/sec to 2.0 mm/sec.