Generation of dense and well-collimated positron beam via ultra-intense laser colliding with a flying plasma layer

With the forthcoming 10-100PW laser facilities, laser-driven electron-positron-pair production has gained particular interest. Here a scheme to enhance the generation of dense electron-positron-pairs is proposed and numerically demonstrated, employing double laser pulses at the intensity level of 10^23 W cm^(-2). The first laser accelerates a thin foil to a relativistic speed via the radiation-pressure-acceleration mechanism and a counter-propagating laser irradiates this flying plasma layer. The simulation results indicate that a high-yield and well-collimated positron beam (~5.5×10^10 positrons/pulse, 8.8nC/pulse) is generated with a large peak density(1.1×10^21 cm^(-3) ) by using tens-of-PW laser pulses.

Evaluation of thermal- nuclear effects from pair-creation in the final fate very-massive stars

Thermonuclear conditions found in explosive massive-stars requirethe use of not only efficient, accurate but thermodynamically consistent stellar equation of state (EOS) routines.The use of tables to describe EoS involved in stellar models is very much needed in understanding the final fate of massive stars. Many massive-low metallicity stars end their life as pair creation supernova (PCSN) through the creation of electron-positron pairs.We used thermodynamically consistent EoS tables to numerically evaluate the thermonuclear effects of the electron electron-positron pair creation in rotating 150 and 200 Massive starsat SMC and rotating and non-rotating 500 M⊙at LMC.As expected, the effect of rotationofreducing the oxygen core masshad increasedthe thermal energy within the threshold of the pair-creation instability.Similarly, lower mass loss stars with SMC model produced higher thermal energies,which can cmpletely explode the stars as PCSNe without remnant.On the other hand, the non-rotating 500 M⊙ might have only reached the instability region due to its lower metallicity (compared to solar metallicity) that iscapable of suppressing the mass loss such that the thermonuclear energy maintains certain amount of elements into the pair creation region. At the final explosion of the stars, the helium core mass educed the thermal energies in trying to avoid the pair-creation region. Many implications of these results for the evolution and explosion of massive stars are discussed.

Nuclear Adiabatic Effects of Electron-Positron Pairs on the Dynamical Instability of Very-Massive Stars

The adiabatic effects of electron-positron pair-production on the dynamical instability of very-massive stars is investigated from stellar progenitors of carbon-oxygen cores within the range of 64 M < MCO < 133 M both with and without rotation. At a very high temperature and relatively low density; the production of electron-positron pairs in the centres of massive stars leads the adiabatic index to below 4/3. The adiabatic quantities are evaluated by constructing a model into a thermodynamically consistent electron-positron equation of state (EoS) table. It is observed that the adiabatic indices in the instability regions of the rotating models are fundamentally positive with central temperature and density. Similarly, the mass of the oxygen core within the instability region has accelerated the adiabatic indices in order to compress the star, while the mass loss and adiabatic index in the non-rotating model exponentially decay. In the rotating models, a small amount of heat is required to increase the central temperature for the end fate of the massive stars. The dynamic of most of the adiabatic quantities show a similar pattern for all the rotating models. The non-rotating model may not be suitable for inducing the instability. Many adiabatic quantities have shown great effects on the dynamical instability of the massive stars due to electron-positron pair-production in their centres. The results of this work would be useful for better understanding of the end fate of very-massive stars.

The effect of gamma quanta absorption due to interaction with thermal bremsstrahlung photons of hot gas in galaxy clusters

The interaction of gamma quantum from distant sources with thermal bremsstrahlung photons of hot intracluster gas with producing electron-positron pair in case of 10 galaxy clusters is considered. It is supposed that intracluster gas in considered clusters is isothermal and electron number density may be described by β distribution with β = 2/3. It is presented that the optical depth due to considered interaction is about 10−8 — 10−.