Our research focused on obtaining a fundamental understanding of the source and properties of EMP at the Titan PW(petawatt)-class laser facility. The project was motivated by data loss and damage to components due to EMP, which can limit diagnostic techniques that can be used reliably at short-pulse PW-class laser facilities. Our measurements of the electromagnetic fields, using a variety of probes, provide information on the strength, time duration, and frequency dependence of the EMP. We measure electric field strengths in the 100's of kV/m range, durations up to 100 ns, and very broad frequency response extending out to 5 GHz and possibly beyond. This information is being used to design shielding to mitigate the effects of EMP on components at various laser facilities. We showed the need for well-shielded cables and oscilloscopes to obtain high quality data. Significant work was invested in data analysis techniques to process this data. This work is now being transferred to data analysis procedures for the EMP diagnostics being fielded on the National Ignition Facility (NIF). In addition to electromagnetic field measurements, we measured the spatial and energy distribution of electrons escaping from targets. This information is used as input into the 3D electromagnetic code, EMSolve, which calculates time dependent electromagnetic fields. The simulation results compare reasonably well with data for both the strength and broad frequency bandwidth of the EMP. This modeling work required significant improvements in EMSolve to model the fields in the Titan chamber generated by electrons escaping the target. During dedicated Titan shots, we studied the effects of varying laser energy, target size, and pulse duration on EMP properties. We also studied the effect of surrounding the target with a thick conducting sphere and cube as a potential mitigation approach. System generated EMP (SGEMP) in coaxial cables does not appear to be a significant at Titan. Our results are directly relevant to planned short-pulse ARC (advanced radiographic capability) operation on NIF.
We apply in this paper the statefinder parameters to the interacting phantom energy with dark matter. There are two kinds of scaling solutions in this model. It is found that the evolving trajectories of these two scaling solutions in the statefinder parameter plane are quite different, and that are also different from the statefinder diagnostic of other dark energy models.PACS numbers: 98.80.Es Cosmic observations indicate that our universe is undergoing an accelerated expansion and the dominated component of the present universe is dark energy [1,2,3,4,5]. The Wilkinson Microwave Anisotropy Probe (WMAP) satellite experiment tells us that dark energy, dark matter, and the usual baryonic matter occupy about 73%, 23%, and 4% of the total energy of the universe, respectively. The accelerated expansion of the present universe is attributed to the dark energy whose essence is quite unusual and there is no justification for assuming that it resembles known forms of matter or energy. Candidates for dark energy have been widely studied and focus on the cosmological constant Λ [6,7] with W = −1, a dynamically evolving scalar field (quintessence) [8,9] with W > −1 and phantom [10] with W < −1. Recently, a study of high-Z (Z is redshift) SNe Ia [11] find that the equation of state of dark energy has a 99% probability of being W < −1 if no priors are placed on Ω 0 m . When these SNe results are combined with CMB and 2dFGRS the 95% confidence limits on an unevolving equation of state are −1.46 < W < −0.78 [3,11] which is consistent with estimates made by other groups [4,5]. In order to obtain W < −1, phantom field with reverse sign in its dynamical term may be a simplest way and can be regarded as one of interesting possibilities describing dark energy [12]. However, the other physical properties of phantom energy are rather weird, as they include violation of the dominant-energy condition, naive superluminal sound speed and increasing energy density with time. The latter property ultimately leads to unwanted future singularity called big rip which had been considered in [13]. This singularity is characterized by the divergence of the scale factor in a finite time in future [14].Many authors have discussed various kinds of phantom field models to avoid the cosmic doomsday [15], which require a special class of phantom field potentials with a local maximum. Moreover, the energy density of the phantom field increases with time, while the energy density of the matter fluid decreases as the universe expands. Why are the energy density of dark matter and the phantom energy density of the same order just at the present epoch? This coincidence problem becomes more difficult to solve in the phantom model without the suitable interaction [16]. But Guo et al. in Ref. [17,18] proposed a suitable interaction in the phantom field model, and the coincidence problem can be avoided. Moreover in Ref.[18], the universe also avoids the big rip. In Ref.[18], considering a universe model which contains phantom field φ and the dark matter ρ ...
Three-dimensional fast magnetic reconnection driven by two ultraintense femtosecond laser pulses is investigated by relativistic particle-in-cell simulation, where the two paralleled incident laser beams are shot into a near-critical plasma layer to form a magnetic reconnection configuration in self-generated magnetic fields. A reconnection X point and out-of-plane quadrupole field structures associated with magnetic reconnection are formed. The reconnection rate is found to be faster than that found in previous two-dimensional Hall magnetohydrodynamic simulations and electrostatic turbulence contribution to the reconnection electric field plays an essential role. Both in-plane and out-of-plane electron and ion accelerations up to a few MeV due to the magnetic reconnection process are also obtained.
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