Weibel instability in hot plasma flows with production of gamma-rays and electron-positron pairs

We present the results of theoretical analysis and numerical simulations of the Weibel instability in two counter-streaming hot relativistic plasma flows, e.g. flows of electron-proton plasma having rest-mass density $\rho \sim 10^{-4}\; \text{g}\, \text{cm}^{-3}$, Lorentz factors $\Gamma \sim 10$ and proper temperature $T \sim 10^{13}\; \text{K}$. The instability growth rate and the filament size at the linear stage are found analytically, and are in qualitative agreement with results of three-dimensional particle-in-cell simulations. In the simulations, incoherent synchrotron emission and pair photoproduction in electromagnetic fields are taken into account. If the plasma flows are dense, fast and/or hot enough, the overall energy of synchrotron photons can be much larger than the energy of generated electromagnetic fields. Furthermore, a sizable number of positrons can be produced due to the pair photoproduction in the generated magnetic field. We propose a rough criterion for judging copious pair production and synchrotron losses. By means of this criterion we conclude that incoherent synchrotron emission and pair production during the Weibel instability can have implications for the collapsar model of gamma-ray bursts.Comment: 15 pages, 7 figures, 1 tabl

Piecewise acceleration of electrons across a periodic solid-state structure irradiated by intense laser pulse

Three-dimensional particle-in-cell simulations show that the periodic solid-state structures irradiated by intense ($\sim 10^{19}$ W/cm${}^2$) laser pulses can generate collimated electron bunches with energies up to 30 MeV (and acceleration gradient of $11.5$ GeV/cm), if the microstructure period is equal to the laser wavelength. A one-dimensional model of piecewise acceleration in the microstructure is proposed and it is in a good agreement with the results of numerical simulations. It shows that the acceleration process for relativistic electrons can be theoretically infinite. In the simulations, the optimal target parameters (the width of the microstructure elements and the microstructure period) are determined. The explored parameters can be used for proof-of-principle experiments demonstrating an ultrahigh gradient acceleration by a number of identical and mutually coherent laser pulses [A. Pukhov et al., Eur. Phys. J. Spec. Top. 223, 1197 (2014)]

Theory of the collapsing axisymmetric cavity

We investigate the collapse of an axisymmetric cavity or bubble inside a fluid of small viscosity, like water. Any effects of the gas inside the cavity as well as of the fluid viscosity are neglected. Using a slender-body description, we show that the minimum radius of the cavity scales like $h_0 \propto t'^{\alpha}$, where $t'$ is the time from collapse. The exponent $\alpha$ very slowly approaches a universal value according to $\alpha=1/2 + 1/(4\sqrt{-\ln(t')})$. Thus, as observed in a number of recent experiments, the scaling can easily be interpreted as evidence of a single non-trivial scaling exponent. Our predictions are confirmed by numerical simulations

In situ dating and investigation of remarkably depleted –27.3‰ SMOW “Slushball” Earth zircons

Paleoproterozoic amphibolites and gneisses - that are remarkably depleted in ^(18)O are found in the Belomorian Belt in Karelia, Russia [1,2]. We mapped their extent to exceed 200x20km and affect metamorphosed mafic intrusions (est. ~2.4 Ga intrusion age) and host 2.6Ga gneisses found in this 1.9 Ga collisional belt. δ^(18)O values of –7 to –27.3‰ characterize minerals and rocks from several of these localities; some of these rocks are also remarkably depleted with respect to δD (-212 to –235‰ amphiboles). All have typical terrestrial Δ^(17)O values of 0‰. Based on previous paleogeographic reconstructions, we attribute the origin of these exotic O and H isotope compositions to the hydrothermal alteration associated with subglacial rifting during the Paleoproterozoic panglobal ice ages, but discuss additional possibilities: extremely low-δ^(18)O Paleo- proterozoic sea water, and excursion of Karelia to polar latitudes. Given that at high-T hydrothermal exchange equilibrium Δ^(18)O(rockwater) is close to zero, but water-rock interaction is rarely 100% efficient, the lowest measured δ^(18)O value in silicates likely gives the upper δ^(18)O bound for the altering meteoric fluid; we thus continues our quest to find the lowest δ^(18)O material such as a mineral assemblage or a tiny zircon fragment that would provide record of δ^(18)Owater

π+\pi^+ and π0\pi^0 Polarizabilities from {γγ→ππ\gamma\gamma\rightarrow\pi\pi} Data on the Base of S-Matrix Approach

We suggest the most model-independent and simple description of the $\gamma\gamma\rightarrow\pi\pi$ process near threshold in framework of S-matrix approach. The amplitudes contain the pion polarizabilities and rather restricted information about $\pi \pi$ interaction. Application of these formulae for description of MARK-II \cite{M2} and Crystal Ball \cite{CB} data gives: $(\alpha-\beta)^{C}=(6.0\pm 1.2)\cdot 10^{-42} {\rm cm}^{3}$, $(\alpha-\beta)^{N}=(-1.4\pm 2.1)\cdot 10^{-42} cm^3$ (in units system $e^2 = 4 \pi \alpha$) at the experimental values of $\pi \pi$ scattering lengths. Both values are compartible with current algebra predictions.Comment: LaTeX, 14 pages plus 6 figures (not included, available upon request) , ISU-IAP.Th93-03, Irkuts

The control system of synchronous movement of the gantry crane supports

The paper presents study findings on synchronization of the gantry crane support movement. Asynchrony moving speed bearings may lead to an emergency mode at the natural rate of deformed metal structure alignment. The use of separate control of asynchronous motors with the vector control method allows synchronizing the movement speed of crane supports and achieving a balance between the motors. Simulation results of various control systems are described. Recommendations regarding the system further application are given

Analytical description of the time-over-threshold method based on the time properties of plastic scintillators equipped with silicon photomultipliers

A new high-granular compact time-of-flight neutron detector for the identification and energy measurement of neutrons produced in nucleus-nucleus interactions at the BM@N experiment, Dubna, Russia, at energies up to 4 AGeV is under development. The detector consists of approximately 2000 fast plastic scintillators, each with dimensions of 40$\times$40$\times$25 mm$^3$, equiped with SiPM (Silicon Photomultiplier) with an active area of 6$\times$6 mm$^2$. The signal readout from these scintillators will employ a single-threshold multichannel Time-to-Digital Converter (TDC) to measure their response time and amplitude using the time-over-threshold (ToT) method. This article focuses on the analytical description of the signals from the plastic scintillator detectors equipped with silicon photomultipliers. This description is crucial for establishing the ToT-amplitude relationship and implementing slewing correction techniques to improve the time resolution of the detector. The methodology presented in this paper demonstrates that a time resolution at the 70 ps level can be achieved for the fast plastic scintillator coupled with silicon photomultiplier with epitaxial quenching resistors

Development of a 100 ps TDC based on a Kintex 7 FPGA for the High Granular Neutron Time-of-Flight detector for the BM@N experiment

The prototype of a TDC board has been developed for the new high granular time-of-flight neutron detector (HGND). The board is based on the standard LVDS 4x asynchronous oversampling using the xc7k160 FPGA with a 100 ps bin width. The HGND is being developed for the BM@N (Baryonic Matter at Nuclotron) experiment to identify neutrons and to measure their energies in heavy-ion collisions at ion beam energies up to 4 A GeV. The HGND consists of about 2000 scintillator detectors (cells) with a size of $40 \times 40 \times 25 mm^3$ and light readout with EQR15 11-6060D-S photodetectors. To measure the time resolution of the scintillator cells, the two-channel FPGA TDC board prototype with two scintillator cells was tested with an electron beam of "Pakhra" synchrotron at the LPI institute (Moscow, Russia). The measured cell time resolution is 146 ps, which is in a good agreement with the 142 ps time resolution measured with a 12-bit @ 5 GS/s CAEN DT5742 digitizer. For the full HGND, the TDC readout board with three such FPGAs will read 250 channels. In total, eight such TDC boards will be used for the full HGND at the BM@N experiment