Magnetic sail is spacecraft propulsion that produces an artificial magnetosphere to block solar wind particles, and thus impart momentum to accelerate a spacecraft. In the present study, we conducted two-dimensional particle-in-cell simulations on small-scale magnetospheres to investigate thrust characteristics of magnetic sail and its derivative, Magneto Plasma Sail (MPS), in which the magnetosphere is inflated by an additional plasma injection. As a result, we found that the electron Larmor motion and the charge separation become significant on such a small-scale magnetosphere and the thrust of magnetic sail is affected by the cross-sectional size of charge-separated magnetosphere. We also revealed that the plasma injection on the condition that the kinetic energy of plasma is smaller than the local magnetic field energy (β~10-3) can significantly inflate the magnetosphere by
tape deteriorated the current transport performance and thermal stability of the HTS coil. The present study contributes to the characterization of HTS coils and design of a coil system for the magnetic sail spacecraft.
We examined the plasma flow response to meso-and microscale magnetic dipoles by performing three-dimensional full particle-in-cell simulations. We particularly focused on the formation of a magnetosphere and its dependence on the intensity of the magnetic moment. The size of a magnetic dipole immersed in a plasma flow can be characterized by a distance L from the dipole center to the position where the pressure of the local magnetic field becomes equal to the dynamic pressure of the plasma flow under the magnetohydrodynamics (MHD) approximation. In this study, we are interested in a magnetic dipole whose L is smaller than the Larmor radius of ions r iL calculated with the unperturbed dipole field at the distance L from the center. In the simulation results, we confirmed the clear formation of a magnetosphere consisting of a magnetopause and a tail region in the density profile, although the spatial scale is much smaller than the MHD scale. One of the important findings in this study is that the spatial profiles of the plasma density as well as the current flows are remarkably affected by the finite Larmor radius effect of the plasma flow, which is different from the Earth's magnetosphere. The magnetopause found in the upstream region is located at a position much closer to the dipole center than L. In the equatorial plane, we also found an asymmetric density profile with respect to the plasma flow direction, which is caused by plasma gyration in the dipole field region. The ion current layers are created in the inner region of the dipole field, and the electron current also flows in the region beyond the ion current layer because ions with a large inertia can closely approach the dipole center. Unlike the ring current structure of the Earth's magnetosphere, the current layers in the microscale dipole fields are not circularly closed around the dipole center. Since the major current is caused by the particle gyrations, the current is independently determined to be in the direction of the electron and ion gyrations, which are the same in both the upstream and downstream regions. The present analysis on the formation of a magnetosphere in the regime of a microscale magnetic dipole is significant for understanding the solar wind response to the crustal magnetic anomalies on the Moon surface, such as were recently observed by spacecraft. V C 2014 AIP Publishing LLC. [http://dx.
This paper reports thermal diffusivities of Bi-system and Y-system tape conductors. First, we measure temperature traces of the bundled conductors for the heater disturbance at conduction cooling conditions. Obtained results are modeled and analyzed using one-dimensional as well as two-dimensional heat balance equations. We show that the analysis results can successfully reproduce the experimental results for a wide temperature range from 20 to 77 K. On the basis of such results, we also clarify that the thermal diffusivity, in the perpendicular direction to the tape surface, of the Y-system conductors are five orders of magnitude lower than that of the Bi-system ones. Our results indicate that the consideration of such low thermal diffusivity is important for the conduction-cooled magnet design.
A magnetic sail is a spacecraft propulsion system that generates an artificial magnetosphere to block solar wind particles and uses the imparted momentum to accelerate a spacecraft. In the present study, we conducted three-dimensional particle-in-cell simulations on small-scale magnetospheres to investigate the thrust characteristics of smallscale magnetic sails. The results show that electron Larmor motion and charge separation become significant in small-scale magnetospheres, and that the thrust of the magnetic sail is affected by the cross-sectional area of the charge-separated plasma cavity. Empirical formulae for the thrust are obtained by changing spacecraft design and solar wind parameters. These equations show that the thrust of small-scale magnetic sail is approximately proportional to magnetic moment, solar wind density and solar wind velocity.
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