Proton Threshold States in the 22Na(p,gamma)23Mg Reaction and Astrophysical Implications

Proton threshold states in 23Mg are important for the astrophysically relevant proton capture reaction 22Na(p,gamma)23Mg. In the indirect determination of the resonance strength of the lowest states, which were not accessible by direct methods, some of the spin-parity assignments remained experimentally uncertain. We have investigated these states with Shell Model, Coulomb displacement, and Thomas-Ehrman shift calculations. From the comparison of calculated and observed properties we relate the lowest relevant resonance state at E=7643 keV to an excited 3/2+ state in accordance with a recent experimental determination by Jenkins et al.. From this we deduce significantly improved values for the 22Na(p,gamma)23Mg reaction rate at stellar temperatures below T_9=0.1K.Comment: 8 pages, 4 figures, 6 table

Adaptation of the de Hoffmann–Teller frame for quasi-perpendicular collisionless shocks

The concept of the de Hoffmann–Teller frame is revisited for a high Mach-number quasi-perpendicular collisionless shock wave. Particle-in-cell simulation shows that the local magnetic field oscillations in the shock layer introduce a residual motional electric field in the de Hoffmann–Teller frame, which is misleading in that one may Interpret that electrons were not accelerated but decelerated in the shock layer. We propose the concept of the adaptive de Hoffmann–Teller (AHT) frame in which the residual convectivefield is canceled by modulating the sliding velocity of the de Hoffmann–Teller frame. The electrostatic potential evaluated by Liouville mapping supports the potential Profile obtained by electric field in this adaptive frame, offering a wide variety of applications in shock wave studies

EMPIRICAL EVIDENCE FOR RELATION BETWEEN THRESHOLD EFFECTS AND NEUTRON STRENGTH FUNCTION

In the present letter one proves, by analyzing experimental data, that the mass-dependent magnitude of threshold effects observed in deuteron stripping reactions on A ≈ 90 mass target nuclei is proportional to the 3p-wave neutron strength function. ‚ ¤ ´´µ°· ¡µÉ¥´ µ¸´µ¢¥ ´ ²¨ § Ô±¸ ¶¥·¨³¥´É ²Ó´ÒÌ ¤ ´´ÒÌ ¶·¨¢µ¤¨É¸Ö ¤µ± § É¥²Ó¸É¢µ ɵ£µ, Îɵ § ¢¨¸¨³ Ö µÉ ³ ¸¸Ò ¢¥²¨Î¨´ ¶µ·µ£µ¢ÒÌ ÔËË¥±Éµ¢,´ ¡²Õ¤ ¥³ÒÌ ¢ ·¥ ±Í¨ÖÌ ¤¥°É·µ´-µ£µ¸É·¨ ¶ ¶¨´£ ´ Ö¤· ̸³ ¸¸µ°A ≈ 90, ¶·µ ¶µ·Í¨o´ ²Ó´ 3p-¢µ²´µ¢µ°´¥°É·µ´´µ°¸¨²µ¢µ°Ë Ê´±Í¨¨

Modelling of Solar Wind Plasma Turbulence for Space Missions of ESA and NASA

The space between planets, stars and galaxies seems to be empty but it is not. It is completely filled with ionised gas called plasma. In our interplanetary neighbourhood this plasma is launched by the Sun. This continuous stream of solar particles interstratified by the interplanetary magnetic field got the name solar wind. It carries a lot of information from the Sun and it is a unique laboratory to study fundamental physics. The solar wind develops quickly into a turbulent state but the driver for this development is far from complete understanding. Especially multi spacecraft missions supported by high performance computer simulations allow a remarkable progress in turbulence physics. The picture of plasma turbulence in the interplanetary space can be now extended in two fashions by means of the numerical parallelised simulation codes. One is the extension to the fifth dimension by including the time or radial evolution of the turbulent state of the solar wind, i.e. the energy spectrum as a function of wave vectors, frequencies, and radial distance or elapsed time from the Sun. The other extension is a wider coverage of scales ranging from fluid treatment of plasmas (10,000 km or larger) down to the kinetic scales of the ion gyroradius (about 100 km). For this purpose the turbulence is generated by DNS (direct numerical simulation) using hybrid - PIC (Particle-In-Cell) codes. The spatial structure of plasma turbulence and its temperature dependence is obtained by incorporating the hybrid plasma code A.I.K.E.F. into direct numerical simulation of astrophysical kinetic turbulence. The resulting ion-scale turbulence is related to the solar wind distance from the Sun by using a mapping procedure

Free Energy Sources in Current Sheets Formed in Collisionless Plasma Turbulence

Collisionless dissipation of macroscopic energy into heat is an unsolved problem of space and astrophysical plasmas, e.g., solar wind and Earth's magnetosheath. The most viable process under consideration is the turbulent cascade of macroscopic energy to kinetic scales where collisionless plasma processes dissipate the energy. Space observations and numerical simulations show the formation of kinetic scale current sheets in turbulent plasmas. Instabilities in these current sheets (CS) can provide collisionless dissipation and influence the turbulence. Spatial gradients of physical quantities and non-Maxwellian velocity distribution functions provide the free energy sources for CS plasma instabilities. To determine the free energy sources provided by the spatial gradients of plasma density and electron/ion bulk velocities in CS formed in collisionless turbulent plasmas with an external magnetic field B0, we carried out two-dimensional particle-in-cell-hybrid simulations and interpret the results within the limitations of the simulation model. We found that ion-scale CS in a collisionless turbulent plasma are formed primarily by electron shear flows, i.e., electron bulk velocity inside CS is much larger than ion bulk velocity while the density variations through the CS are relatively small (<10%). The electron bulk velocity and, thus, the current density inside the sheets are directed mainly parallel to B0. The shear in the perpendicular electron and ion bulk velocities generates parallel electron and ion flow vorticities. Inside CS, parallel electron flow vorticity exceeds the parallel ion flow vorticity, changes sign around the CS centers, and peaks near the CS edges. An ion temperature anisotropy develops near CS during the CS formation. It has a positive correlation with the parallel ion and electron flow vorticities. Theoretical estimates support the simulation results

The ergodicity of the two dimensional systems

Consiglio Nazionale delle Ricerche (CNR). Biblioteca Centrale / CNR - Consiglio Nazionale delle RichercheSIGLEITItal