Secondary Charge Exchange Research Articles

ON THE STABILITY OF PICK-UP ION RING DISTRIBUTIONS IN THE OUTER HELIOSHEATH

The energetic neutral atom (ENA) hypothesis for the ribbon feature observed by the Interstellar Boundary Explorer (IBEX) posits that the neutral component of the solar wind continues beyond the heliopause and charge exchanges with interstellar ions in the Outer Heliosheath (OHS). This creates pick-up ions that gyrate about the draped interstellar magnetic field (ISMF) lines at pitch angles near 90° on the locus where the ISMF lies tangential to the heliopause and perpendicular to the heliocentric radial direction. This location closely coincides with the location of the ribbon feature according to the prevailing inferences of the ISMF orientation and draping. The locally gyrating ions undergo additional charge exchange and escape as free-flying neutral atoms, many of which travel back toward the inner solar system and are imaged by IBEX as a ribbon tracing out the locus described above. For this mechanism to succeed, the pick-up ions must diffuse in pitch angle slowly enough to permit secondary charge exchange before their pitch angle distribution substantially broadens away from 90°. Previous work using linear Vlasov dispersion analysis of parallel propagating waves has suggested that the ring distribution in the OHS is highly unstable, which, if true, would make the secondary ENA hypothesis incapable of rendering the observed ribbon. In this paper, we extend this earlier work to more realistic ring distribution functions. We find that, at the low densities necessary to produce the observed IBEX ribbon via the secondary ENA hypothesis, growth rates are highly sensitive to the temperature of the beam and that even very modest temperatures of the ring beam corresponding to beam widths of <1° are sufficient to damp the self-generated waves associated with the ring beam. Thus, at least from the perspective of linear Vlasov dispersion analysis of parallel propagating waves, there is no reason to expect that the ring distributions necessary to produce the observed IBEX ENA flux via the secondary ENA hypothesis will be unstable to their own self-generated turbulence.

SCATTER-FREE PICKUP IONS BEYOND THE HELIOPAUSE AS A MODEL FOR THE INTERSTELLAR BOUNDARY EXPLORER RIBBON

We present a new kinetic-gasdynamic model of the solar wind interaction with the local interstellar medium. The model incorporates several processes suggested earlier for the origin of the ribbon—the most prominent feature seen in the all-sky maps of heliospheric energetic neutral atoms (ENAs) discovered by the Interstellar Boundary Explorer (IBEX). The ribbon is a region of enhanced fluxes of ENAs crossing almost the entire sky. Soon after the ribbon's discovery, it was realized that the enhancement of the fluxes could be in the directions where the radial component of the interstellar magnetic field around the heliopause is close to zero. Our model includes secondary charge exchange of the interstellar H atoms with the interstellar pickup protons outside the heliopause. Previously, in the frame of a kinetic-gasdynamic model where pickup protons are treated as a separate kinetic component, it was shown that the interstellar pickup protons outside the heliopause may be a significant source of ENAs at energies above 1 keV. The key difference between the current work and the previous models is in the assumption of no pitch-angle scattering for newly created pickup protons outside the heliopause. We demonstrate that in the limit of no pitch-angle scattering ribbon of enhanced ENA fluxes appears in the model, and this may qualitatively explain the ribbon discovered by IBEX.

Possibility of using active secondary charge-exchange particle diagnostics for measuring the magnetic field direction in the plasma of a magnetic fusion reactor

An active particle diagnostic method based on the secondary charge exchange of hydrogen atoms of a probing (diagnostic) beam is proposed for local measurements of the magnetic field direction in the plasma of a thermonuclear fusion reactor. Experiments with new-generation large devices require searching for novel methods for measuring the direction of the total magnetic field in a plasma at different points along the radius of the plasma column. The main idea of the method proposed, which holds great promise for large devices, is outlined. The possibility of using the method on ITER—a large fusion reactor that is now at the design stage—is illustrated by carrying out relevant numerical simulations. The results obtained for one of the main discharge scenarios, with the injection geometry and probing beam energy (100 eV) that are now adopted for the ITER design, show that the method can provide local measurements of the magnetic field direction (the magnetic pitch angle) and of the spatial variations of the field vector. Further analysis has revealed, however, that, from the standpoint of signal intensity and signal-to-noise ratio, it is expedient to increase the energy of the beam atoms to 200–250 keV. With such probing beams, the method ensures a spatial (radial) resolution of about 10 cm in the plasma core during a signal acquisition time of 10 ms. The magnetic pitch angle can be measured with an accuracy of 5 × 10−3 rad. An important advantage of the method proposed is its ability to directly measure the pitch angle of the magnetic field lines.

Time-resolved spectroscopy of Ar II recoil ions in the 300-600 nm wavelength range

Radiative emission, in the 300-600 nm wavelength range of Ar II recoil ions produced by the impact of a 6.8 MeV amu-1 Xe42+ pulsed ion beam on an argon target has been studied using a time resolved fluorescence technique. Excited states in Ar II are found to be due to the primary impact but also to secondary charge exchange collisions. Radiative lifetimes and secondary relaxation times are determined from fluorescence decays.

Jovian magnetospheric neutral wind and auroral precipitation flux

We propose a mechanism for the transport of energy from the rotation of Jupiter into the heavy ions whose precipitation into the atmosphere is responsible for the intense ultraviolet aurora. The process involves charge exchange of heavy ions in the Io torus, their flight to the outer magnetosphere as neutrals, and their reionization in a region where the pickup magnetic moment is large. The particles diffuse back inward adiabatically and are precipitated at 9 RJ with an energy exceeding 10 keV/nucleon. A field and flow model based on Voyager observations is used that defines a source region extending from 32 RJ to 80 RJ on the nightside. This region is capable of delivering 4×1013 W of power to the auroral region, well within the realm of the power required by observations. We also demonstrate that this mechanism provides a neutral planetary wind from Jupiter. The predicted wind will consist of two beams: one intense (5×1028 s−1) at 25 eV/nucleon and the other tenuous (1×1025 s−1) at 600 eV/nucleon and above. These neutral particles will appear as a suprathermal heavy ion component in the solar wind.

The application of charge independence to the nuclear capture of Negative K-mesons

The results of the charge independence hypothesis are compared with the existing experimental data on the nuclear capture of negative K-mesons. The comparison of the calculated gS− /gS+ and π−/π+ emission ratios with the experimental ones strongly suggest the dominance of theT= 1 state (1) over theT= 0 state in the primary act. Furthermore, the π−/π+ emission ratio is shown to give an estimate of the branching ratio between gS emission and Λ0 emission, which is free from the ambiguities due to the secondary absorption of the products of the primary act or due to the difficulties of detecting neutral particles and is only slightly affected by secondary charge exchange scatterings of the product particles. The preliminary value thus determined by using the experimental data thus far available for the π−/π+ emission ratio, suggests that gS emission is more favored than Λ0 emission in the primary act. The implications of measuring the positive-to-negative ratio of high energy π-mesons emitted from K− captures is discussed in some detail and a few experiments are proposed in this connection.