Ray-tracing simulations of whistler-mode wave propagation in different rescaled dipole magnetic fields

Kinetic simulation is a powerful tool to study the excitation and propagation of whistler-mode waves in the Earth’s inner magnetosphere.This method typically applies a scaled-down dipole magnetic field to save computational time.However,it remains unknown whether whistler wave propagation in the scaled-down dipole field is consistent with that in the realistic dipole field.In this work,we develop a ray-tracing code with a scalable dipole magnetic field to address this concern.The simulation results show that parallel whistler waves at different frequencies gradually become oblique after leaving the equator and propagate in different raypaths in a dipole magnetic field.During their propagation,the higher frequency waves tend to have larger wave normal angles at the same latitude.Compared with the wave propagation in a realistic dipole field,the wave raypath and wave normal remain the same,whereas the wave amplification or attenuation is smaller because of the shorter propagation time in a scaled-down dipole field.Our study provides significant guidance for kinetic simulations of whistler-mode waves.

Asymmetry of Neoclassical Transport by Dipole Electric Field

Effects of dipole electric fields on neoclassical transport are studied. Large asym-metry in transport is created. The dipole fields, which are in a negative R-direction, reduce theion drift, increase electron drift, and change the steps of excursion due to collisions. It is foundthat different levels of dipole field intensities have different types of transport. For the lowestlevel of the dipole field, the transport returns to the neoclassical one. For the highest level of thedipole field, the transport is turned to be the turbulence transport similar to the pseudo-classicaltransport. Experimental data may be corresponded to a large level of the dipole field intensity.

A Simple Mechanism for Generating a Geomagnetic Field

On the basis of the ideal gas model, the polarization of charges in the mantle was obtained, a physical and mathematical model was constructed, and estimated calculations of the dipole mode of the Earth’s magnetic field were performed, taking into account the speed of its angular rotation, the parameters of density and temperature, the chemical composition, the ionization potential, the dielectric constant and the percentage of the main chemical compounds of the mantle substance.

Optimization of the three-dimensional electric f ield in IH-DTL

The tuning process of the three-dimensional electric field near the beam axis is very important in the optimization of the Interdigital H-mode Drift Tube Linac （IH-DTL）. The tuning of the longitudinal field distribution, the Kilpatrik （Kp） factor, and the transverse dipole field have been discussed in detail, combined with the radio-frequency tuning process of the 53.667 MHz short IH-DTL cavity, which was designed to accelerate 238 U 34＋ from 0.143 MeV/u to 0.289 MeV/u in the SSC-Linac injector project at the Institute of Modern Physics. The flatness criterion and the tube tuning method are discussed in order to meet the beam dynamics requirements. In the tube tuning process, the energy gain error in the cells should be reduced to less than ± 2%, and the Kp factor should be reduced to 1.6. The transverse dipole field and the method that uses a ＂plunger＂ to dismiss this dipole field are evaluated. The experience gained from the first cavity optimization benefits the tuning process of the three remaining IH-DTL cavities in the SSC-Linac project.

Spontaneous positive exchange bias effect in SrFeO_(3-x)/SrCoO_(3-x) epitaxial bilayer

A novel phenomenon of spontaneous positive exchange bias(PEB)is reported in SrFeO_(3-x)/SrCoO_(3-x) epitaxial bilayer without undergoing any magnetic field treatment.When inserting a thick SrTiO3(STO)nonmagnetic spacer(about 6 nm)into the bilayer interface,this phenomenon still exists.Based on a series of testing means,the spontaneous PEB effect is supposed to be mainly related to short-range ferromagnetic(FM)exchange coupling at the interface when there is no STO spacer.As the STO interlayer reaches up to a certain thickness,shortrange coupling interaction basically disappears.At this time,the long-range dipole field may be responsible for the coupling of the FM and antiferromagnetic(AFM)layer across the nonmagnetic STO and then leads to the same bias effect.Our discoveries provide a new way to realize and manipulate spontaneous exchange bias-based spintronics devices,such as magnetic recording heads and spin valves.