Influence of the temperature of the photosphere and deeper layers of the Sun on the spectra of gamma quanta with energies above 511 keV during solar flares

Gamma-ray quanta, which occur during solar flares due to the interaction of accelerated protons with the photosphere and deeper layers of the sun, enter interplanetary space from a thickness of several tens of g/cm2. In the presented work, gamma quanta with energies of more than 511 keV are considered. This makes it possible to exclude from consideration the dependence of the probability of ortho- and parapositronium formation on the temperature and density of the solar matter. And also do not consider the probability of annihilation by two or 3 gamma quanta. Thus, the reactions of thermal neutrons remain dependent on the temperature. As the ambient temperature increases, the average number of elastic neutron scattering before capture increases. This leads to a more likely penetration of neutrons to a greater depth or their departure into the interplanetary space. The high temperature of the Sun below the photosphere may be one of the reasons for the absence of the 2.223 MeV line in solar flares with registered protons in the PAMELA and AMS2 experiments. Using the GEANT4 package, the spectra of gamma-quanta arising in nuclear interactions are calculated. The temperature-dependent features of the gamma-ray spectra are discussed.

Laser-accelerated protons using density gradients in hydrogen plasma spheres

The effect of different density profiles on micron-sized hydrogen plasma spheres is investigated when the plasma gets irradiated with an ultrashort circularly polarized laser. In this study, we show that significant improvement in the characteristics of the accelerated protons viz. maximum proton energy, as well as their monoenergetic behaviour, is possible by using a plasma sphere having a tailored density profile. A linear-shaped density inhomogeneity is introduced in the plasma sphere such that the density is peaked at the centre and gradually dropping outwards. The density gradient is tuned by changing the peak density at the centre. The optimum regime of steepness is found for the maximum energy attained by the protons where the target is opaque enough for the radiation pressure to play its role, however not too opaque to inhibit efficient target heating. A novel Gaussian-shaped density profile is suggested which plays an important role in suppressing the sheath field. With a decreased rear-side field, a visible improvement of the monoenergetic feature of the protons is observed.

Enhanced Proton Acceleration by Laser-Driven Collisionless Shock in the Near-Critical Density Target Embedding with Solid Nanolayers

Effects of solid nanolayers embedded in a near-critical density plasma on the laser-driven collisionless shock acceleration are investigated by using two-dimensional particle-in-cell simulations. Due to the interaction of nanolayers and the incident laser, an additional number of hot electrons are generated and an inhomogeneous magnetic field is induced. As a result, the collisionless shock is reinforced within the nanolayer gaps compared to the target without the structured nanolayers. When the laser intensity is 9.8 × 10 19 W / cm 2 , the amplitude of the electrostatic field is increased by 30% and the shock velocity is increased from 0.079c to 0.091c, leading to an enhancement of the peak energy and the cutoff energy of accelerated protons, from 6.9 MeV to 9.1 MeV and 12.2 MeV to 20.0 MeV, respectively. Furthermore, the effects of the width of the nanolayer gaps are studied, by adjusting the gap width of nanolayers, and optimal nanolayer setups for collisionless shock acceleration can be acquired.