Naoki Bessho

Electron acceleration to ultrarelativistic energies in a collisionless oblique shock wave

Electron motion in an oblique shock wave is studied by means of a one-dimensional, relativistic, electromagnetic, particle simulation code with full ion and electron dynamics. It is found that an oblique shock can produce electrons with ultrarelativistic energies; Lorentz factors with γ≳100 have been observed in our simulations. The physical mechanisms for the reflection and acceleration are discussed, and the maximum energy is estimated. If the electron reflection occurs near the end of a large-amplitude pulse, those particles will then be trapped in the pulse and gain a great deal of energy. The theory predicts that the electron energies can become especially high at certain propagation angles. This is verified by the simulations.

Electron acceleration and trapping by an oblique shock wave

Electron acceleration to ultrarelativistic energies by an oblique magnetosonic shock wave is studied. First, the maximum electron energy is analytically obtained with new simple calculations. The physical mechanism is also discussed in detail. In the wave frame, electrons reflected near the end of the main pulse region, which will be trapped, gain energy from the electric potential and constant electric field Ey0 perpendicular to the external magnetic field. For certain plasma parameters, these electrons can move a long distance in the direction of Ey0 and obtain a great amount of energy from Ey0. It is argued that the trapped electrons can hardly escape from the shock wave. Next, one-dimensional, relativistic, particle simulations are carried out. Theoretical estimates such as the maximum electron energy are found to be in good agreement with the simulations. Simulations also show that the number of trapped electrons continually increases with time.

In-plane electric fields in magnetic islands during collisionless magnetic reconnection

Magnetic islands are a common feature in both the onset and nonlinear evolution of magnetic reconnection. In collisionless regimes, the onset typically occurs within ion-scale current layers leading to the formation of magnetic islands when multiple X lines are involved. The nonlinear evolution of reconnection often gives rise to extended electron current layers (ECL) which are also unstable to formation of magnetic islands. Here, we show that the excess negative charge and strong out-of-plane electron velocity in the ECL are passed on to the islands generated therein, and that the corresponding observable distinguishing the islands generated in the ECL is the strongly enhanced in-plane electric fields near the island core. The islands formed in ion-scale current layers do not have these properties of the ECL-generated islands. The above result provides a way to assess the occurrence and importance of extended ECLs that are unstable to island formation in space and laboratory plasmas.

Acceleration of energetic ions by nonlinear magnetosonic waves

Interactions of nonthermal energetic ions with nonlinear magnetosonic waves are studied by means of a one-dimensional (one space coordinate and three velocity components), relativistic, electromagnetic particle simulation code with full ion and electron dynamics. It is found that, if ions with gyration speeds much greater than the Alfven speed encounter a shock wave, some of them can gain great energies. The acceleration takes place when the particle velocity becomes nearly parallel to the transverse electric field in the shock. On the basis of a simple physical picture, the increase in the energy is theoretically obtained. Both the theory and simulation show that the ions with higher energies can obtain greater energies. Thus, in a plasma with strong magnetohydrodynamic turbulence some of the ions could be repeatedly accelerated to higher energies by many nonlinear pulses.

Energies of ultrarelativistic electrons produced by an oblique shock wave

Production of ultrarelativistic electrons in an oblique magnetosonic shock wave is studied theoretically and numerically. First, the structure of the oblique shock wave is analytically discussed on the basis of a relativistic, two-fluid model. Then, by use of the field strengths thus obtained, the maximum energy of accelerated electrons is calculated as a function of the propagation speed and angle of the shock wave. Next, a one-dimensional, relativistic, electromagnetic, particle simulation code is used to further investigate the shock propagation and associated electron acceleration. Lorentz factors of accelerated electrons can exceed 100. Detailed comparisons are made between the theoretically predicted field strengths and electron energy and those obtained by the simulations.

Production of Ultrarelativistic Electrons by Oblique Magnetosonic Shock Waves

Electron motion in an oblique magnetosonic wave is studied by means of a one-dimensional, relativistic, electromagnetic particle code with full ion and electron dynamics. It is found that high-energy electrons can be produced; electrons with Lorentz factors γ> 100 have been observed in the simulations. They are reflected and then trapped by the wave. This phenomenon occurs in a large-amplitude oblique shock in a strong magnetic field such that (omega_{rm ce} gtrsim omega_{rm pe}). The acceleration mechanism is given, and the dependence of γ on plasma parameters, such as the propagation angle, is discussed.

Drying of Dielectric Resin Coatings in the Presence of Polycondensation

ABSTRACT Drying of dielectric resin coatings is accompanied simultaneously by evaporation of multicomponent solvents and polycondensation from monomers. The characteristic of the drying is studied experimentally. As a test sample, a vanish consisting of trimellitic acid anhydride and 4.41-diphenylmethane diisocyanate dissolved in the mixture of N-methylpyrrolidone and xylene is coated on an aluminum pan. The sample is subjected in drying in two types of dryers: hot air heating and radiation heating. The constant drying rate period is not observed in any run. The maximum drying rate of the sample is lower than the evaporation rate from the solvent layer with no resin. There are remarkable fluctuations in the drying rate in the decreasing drying rate period. The fluctuations are caused by bubble formation. The progress of the reaction can be followed by IR spectroscopic analysis. From these results it is suggested that removal of the solvent and the product is inhibited by the formation of a polymer skin on...

HEAT AND MASS TRANSFER WITH POLYCONDENSATION IN RESIN FILM DURING DRYING

ABSTRACT In a drying process of dielectric resin films coated on electric conductive substances, phenomena such as polymerization of monomers, by-products yield, shrinkage and stress generation lake place simultaneously in addition to heat and mass transfer. For the enhancement of the drying with high efficiency and high quality, it is important to understand the drying mechanism. In this paper, the characteristics of heat and mass transfer in the resin film including polycondensation reaction are presented. The apparent drying rate of polyamideimide varnish films was measured in two different heating modes of radiation and convection. The reaction rate of polycondensation was analyzed both by the thermogravimetry and the differential scanning calorimetry. The apparent drying rate began to drop remarkably when the reaction rate became significant. It implies that the diffusion of the solvent is inhibited by skinning at the surface. Applying the Vrentas/Duda free-volume diffusion model to the prediction of...