We report the optical design of a solid immersion mirror (SIM) incorporated with a flying slider -called a SIM slider -for a near-field recording (NFR) system, its fabrication process, and optical evaluation. To achieve diffraction-limited performance $=14 (rms), a two-step glass-molding process was employed to fabricate the SIM. The numerical aperture of the SIM slider was 1.29. The rms value of the total wavefront aberration was 0:0679. The fabricated SIM slider achieves the optical performance estimated by calculation with the fabrication errors considered, and even diffraction-limited performance. However, an rms value of 0:035-0:04 for the total wavefront aberration is generally assigned for condensing optics for practical use because not only condensing optics but also other optical elements are involved in a practical optical disc system. Therefore, the aberration caused by the fabrication errors in the molding process should be reduced to at least 59% of the present level, if the SIM is to be applied to a practical NFR system.
Energization at a quasi-perpendicular shock is described for ions which approach the shock with a speed much less than that of the incoming plasma. These ions may be trapped between the shock electrostatic potential and the upstream Lorentz force and accelerated by "surfing" along the shock surface, before eventually escaping the shock into the upstream or downstream plasma. The process is described in detail, extending previous work on the mechanism, and energy gains are calculated. It is pointed out that pickup ions in the solar wind are ideally configured, so that a reasonable fraction of the ions can be accelerated by this mechanism at cometary bow shocks, the solar wind termination shock, and interplanetary traveling shocks. The mechanism may provide the required "injection" or preacceleration at quasi-perpendicular shocks for subsequent diffusive shock acceleration.
The modulational instability and collapse of waves in the vicinity of the lower-hybrid resonance including both magnetosonic and lower-hybrid waves are investigated by analytical and numerical methods. The mechanism leading to the modulational instability is the nonlinear coupling of lower-hybrid waves with the much lower-frequency quasineutral density perturbations via the ponderomotive force. The result is a filamentation of the high-frequency field producing elongated, cigar-shaped nonlinear wave packets aligned along the magnetic field with the plasma expelled outside (cavities). The analytical self-similar solutions describing cavity collapse are obtained and compared with the results of numerical simulation for both two- and three-dimensional cavity geometries. It is shown that in three-dimensional solutions the transverse, with respect to the magnetic field, contraction remains prevailing. The possibility of ion acceleration as the result of the lower-hybrid collapse is discussed and detailed comparison is made with the observations of the phenomena in the auroral ionosphere.
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