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Register a new userStellar dynamos with $vec{Omega}times vec{J}$ effect
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We study axisymmetric mean-field dynamo models containing differential rotation, the $alpha$ effect and the additional turbulent induction effects. The additional effects result from the combined action of rotation and an inhomogeneity of the large-scale magnetic field. The best known of them is the $vec{Omega}timesvec{J}$ effect. We also include anisotropic diffusion and a new dynamo term which is of third order in the rotation vector $vec{Omega}$ The model calculations are carried out using the rotation profile of the Sun as obtained from helioseismic measurements and radial profiles of other quantities according to a standard model of the solar interior. In addition, we consider a dynamo model for a full sphere which is solely based on the joint induction effects of rotation and an inhomogeneity of the large-scale magnetic field, without differential rotation and the $alpha$ effect (a $delta^{2}$ dynamo model). This kind of dynamo model may be relevant for fully convective stars.
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One special interest for the industrial development of Hall thruster is characterizing the anomalous cross-field electron transport observed after the channel exit. Since the ionization efficiency is more than 90%, the neutral atom density in that domain is so low that the electron collisions cannot explain the high electron flux observed experimentally. Indeed this is 100 times higher than the collisional transport. In Hall thruster geometry, as ions are not magnetized the electric and magnetic field configuration creates a huge difference in drift velocity between electrons and ions, which generates electron cyclotron drift instability or $vec E times vec B$ electron drift instability. Here we are focusing on collision-less chaotic transport of electrons by those unstable modes generated by $vec E times vec B$ drift instability. We found that in presence of these electrostatic modes electron dynamics become chaotic. They gain energy from the background waves which increases electron temperature along perpendicular direction by a significant amount, $T_{rm perp}/T_{rm parallel}sim 4$, and a significant amount of crossfield electron transport is observed along the axial direction.
The spin correlation coefficent combinations A_{xx}+A_{yy} and A_{xx}-A_{yy}, the spin correlation coefficients A_{xz} and A_{zz}, and the analyzing power were measured for vec p vec p --> d pi^+ between center-of-mass angles 25 deg leq theta leq 65 deg at beam energies of 350.5, 375.0 and 400.0 MeV. The experiment was carried out with a polarized internal target and a stored, polarized beam. Non-vertical beam polarization needed for the measurement of A_{zz} was obtained by the use of solenoidal spin rotators. Near threshold, only a few partial waves contribute, and pion s- and p-waves dominate with a possible small admixture of d-waves. Certain combinations of the observables reported here are a direct measure of these d-waves. The d-wave contributions are found to be negligible even at 400.0 MeV.
A first measurement of longitudinal as well as transverse spin correlation coefficients for the reaction $vec{p}vec{p}to pnpi^+$ was made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for this reaction at 325, 350, 375 and 400 MeV beam energy. The spin correlation coefficients $A_{xx}+A_{yy}, A_{xx}-A_{yy}, A_{zz}, A_{xz},$ and the analyzing power $A_{y},$ as well as angular distributions for $sigma(theta_{pi})$ and the polarization observables $A_{ij}(theta_{pi})$ were extracted. Partial wave cross sections for dominant transition channels were obtained from a partial wave analysis that included the transitions with final state angular momenta of $lleq 1$. The measurements of the ${vec{p}vec{p}to pnpi^{+}}$ polarization observables are compared with the predictions from the Julich meson exchange model. The agreement is very good at 325 MeV, but it deteriorates increasingly for the higher energies. At all energies agreement with the model is better than for the reaction ${vec{p}vec{p}to pppi^{0}}$.
Beam-recoil transferred polarizations for the exclusive $vec{e}p to eK^+ vec{Lambda},vec{Sigma}^0$ reactions have been measured using the CLAS spectrometer at Jefferson Laboratory. New measurements have been completed at beam energies of 4.261 and 5.754 GeV that span a range of momentum transfer $Q^2$ from 0.7 to 5.4 GeV$^2$, invariant energy $W$ from 1.6 to 2.6 GeV, and the full center-of-mass angular range of the $K^+$ meson. These new data add to the existing CLAS $K^+Lambda$ measurements at 2.567 GeV, and provide the first-ever data for the $K^+Sigma^0$ channel in electroproduction. Comparisons of the data with several theoretical models are used to study the sensitivity to s-channel resonance contributions and the underlying reaction mechanism. Interpretations within two semi-classical partonic models are made to probe the underlying reaction mechanism and the $sbar{s}$ quark-pair creation dynamics.
Polarization transfer in the 4He(e,ep)3H reaction at a Q^2 of 0.4 (GeV/c)^2 was measured at the Mainz Microtron MAMI. The ratio of the transverse to the longitudinal polarization components of the ejected protons was compared with the same ratio for elastic ep scattering. The results are consistent with a recent fully relativistic calculation which includes a predicted medium modification of the proton form factor based on a quark-meson coupling model.
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