Yoshihiro Kajimura

Thrust Evaluation of Magneto Plasma Sail by Using Three-Dimensional Hybrid PIC Code.

Magneto Plasma Sail (MPS) is a propulsion system used in space, which generates its force by the interaction between solar wind and an inflated magnetic field via a plasma injection. The quantitative evaluation of the thrust increment generated by injecting a plasma jet with a βin less than unity was conducted by three-dimensional hybrid particle-incell (PIC) simulations in an ion inertia scale. The injected plasma beta βin is 0.02 and the ratio of Larmor radius of injected ion to the representative length of the magnetic field is 0.5 at the injection point. In this situation, the obtained thrust of the MPS is 1.6 mN compared with the 0.2 mN of the thrust obtained by the pure magnetic sail since the induced current region on magnetosphere expanded by the magnetic inflation. The magnetic inflation was achieved by the loop-like current induced by the isotropic injection of plasma with grad B drift motion having the same direction as the original coil current.

Full Particle-in-Cell Simulation Study on Magnetic Inflation Around a Magneto Plasma Sail

In order to consider a next-generation space propulsion system referred to as the “magneto plasma sail,” the magnetic inflation mechanism of a small artificial magnetosphere is investigated. We carry out a two-and-half-dimensional full particle-in-cell simulation, and magnetic inflation mediated by the gyration motion of injected ions is observed. As a result of the gyration motion, an ion-rich region is formed near the direction-reversal position of the injected ions. Magnetic inflation takes place due to the flow of electrons toward the ion-rich region, which carries the field lines of the original magnetosphere. This inflation process is effective for a magnetosphere with a scale comparable to the gyration radius of the injected ions. If the original magnetosphere is much smaller than this, background electrons flow into the ion-rich region outside the magnetosphere, and the inflated magnetosphere is confined to a smaller region. In addition, the thermal effects of background electrons have a similar impact on the inflation process, even if the direction-reversal position is located inside the magnetosphere.

Application of a total variation diminishing scheme to electromagnetic hybrid particle-in-cell plasma simulation

Abstract A discretization procedure for a total variation diminishing (TVD) scheme is introduced to an electromagnetic hybrid particle-in-cell (PIC) plasma simulation code in order to improve the numerical stability and resolution when calculating the plasma flow field in which magnetic field discontinuities (for example, Rankine–Hugoniot jump conditions for shock waves) are generated. In the hybrid PIC code used in this study, ions are treated as particles and electrons are assumed to be an inertia-less (mass-less) fluid. In the numerical results of one-dimensional test simulations, the TVD scheme significantly prevents non-physical, numerical oscillations, which would ordinarily be produced in the solution when the convection term of the magnetic induction equation in the hybrid PIC code is discretized by central difference schemes at magnetic field discontinuities. Furthermore, a two-dimensional simulation of the global structure of a collision-less bow shock, which is suitable for practical use, makes it possible to clearly capture the bow shock by using the hybrid PIC code with the TVD scheme.

Magnetoplasma Sail with Equatorial Ring-current

A magnetoplasma sail (MPS) spacecraft produces an artificial magnetosphere to reflect the solar wind particles approaching the coil, and the corresponding repulsive force exerts on the coil to accelerate the spacecraft in the solar wind direction. In this paper, numerical study of plasma equilibrium in an artificial magnetosphere in interplanetary space is updated to check if the idea of plasma equilibrium is applicable to for MPS or not. It is numerically shown that releasing a low-velocity plasma from an MPS spacecraft excites an equatorial ring-current, which makes a larger magnetosphere and correspondingly a larger thrust level becomes possible. Thrust gain, which is defined as a thrust ratio between MPS and pure magnetic sail without releasing plasma, was found to be as much as 40; this thrust gain is predicted from a limited model describing the interaction between a dipole magnetic field and ions. In addition to the limited simulation, some full numerical simulations of MPS, including a solar wind to magnetosphere interaction as well as plasma equilibrium in a magnetosphere, were conducted to indicate a thrust gain as much as 3.77 is possible in an MHD regime.

Numerical Life Qualification of Ion Thruster’s Ion Optics using the JIEDI Tool

The JIEDI (JAXA’s Ion Engine Development Initiative) tool has been developed to assess the ion acceleration grid erosion of an ion thruster. The sensitivity analysis of the input parameters of the JIEDI tool is conducted in this paper. We compare the simulation results of the JIEDI tool and show that it successfully reproduces the full lifetime test of the μ10 prototype model. Through sensitivity analysis, we found that the sticking factor is the most sensitive input parameter when estimating the accelerator grid erosion and electron backstreaming time. For the worst case scenario of grid erosion (without re-deposition), the uncertainty in the neutral mass flow rate through grid holes is important when estimating the accelerator grid erosion. A 30% change in the neutral mass flow rate caused by a 6% change in the propellant utilization efficiency, corresponds to about a 20% change in the accelerator grid mass loss as well as the increasing rate of minimum potential on the axis of the ion optics. In contrast to the accelerator grid erosion, the uncertainties in the discharge voltage and grid gap (that affect the trajectory of the mainstream ions), are important when estimating decelerator grid erosion. A 40% change in the discharge voltage corresponds to about a 90% change in the decelerator grid mass loss. In addition, a 30% change in the grid gap between the screen grid and the accelerator grid corresponded to about a 40% change in the decelerator grid mass loss.

Numerical Lifetime Evaluation of Ion Thruster's Ion Optics using the JIEDI Tool

The JIEDI (JAXA’s Ion Engine Development Initiative) tool has been developed as a numerical tool for the lifetime qualification of ion thruster’s ion optics with high precision and accuracy. The numerical wear test from beginning-of-life to end-of-life (EOL) by the JIEDI tool was conducted for the ion optics of HAYABUSA’s microwave ion thruster (10 engineering model (EM)). It becomes clear that the erosion profiles for high ion beam current hole are most important to estimate the EOL of 10EM ion optics. The ion optics of 10EM ion thruster encounters its EOL by structural failure of the decelerator grid, which is mainly caused by sputtering of ions and neutrals scattered by elastic collisions. The estimated lifetime of the ion optics is 545 khours at the longest. Through the numerical wear test for 10EM ion optics, the process for lifetime estimation of ion optics by the JIEDI tool was demonstrated.

Experimental and Numerical Investigations on the Thrust Production Process of Magnetoplasma Sail

Research status of spacecraft propulsion using the energy of the solar wind in Japan is overviewed. Experimental and numerical studies showed that moderately sized magnetic sails in the ion inertial scale magnetosphere (~100 km) could produce Newton-class thrust. In the same scale length, magnetic cavity size was successfully controlled in the laboratory experiment of magnetic sail with a plasma jet (Magnetoplasma sail, MPS), but so far, no significant thrust increment was observed in the experiment. On the contrary, MPS concept was tested in MHD scale by numerical simulation, and thrust increment from pure MagSail to MPS as much as 90% was obtained. Currently, we are continuing our experimental and numerical efforts to make a feasibly sized Magnetoplasma sail (10~100 km magnetosphere) in a transitional regime between ion scale and MHD scale by optimizing the magnetic field inflation process of MPS.

Numerical Simulation of Plasma Behavior in a Magnetic Nozzle of a Laser-plasma Driven Nuclear Electric Propulsion System

Numerical simulations of plasma behavior in a magnetic nozzle of a Laser‐Plasma Driven Nuclear Electric Propulsion System are conducted. The propellant is heated and accelerated by the laser and expanded isotropically. The magnetic nozzle is a combination of solenoidal coils and used to collimate and guide the plasma to produce thrust. Simulation calculations by a three‐dimensional hybrid code are conducted to examine the plasma behaviors in the nozzle and to estimate the thrust efficiency. We also estimate a fraction (α) of plasma particles leaking in the forward (spacecraft) direction. By a combination of a few coils, we could decrease α value without degrading the thrust efficiency. Finally, the shaped propellant is proposed to increase the thrust efficiency.