Rei Kawashima

A hyperbolic-equation system approach for magnetized electron fluids in quasi-neutral plasmas

A new approach using a hyperbolic-equation system (HES) is proposed to solve for the electron fluids in quasi-neutral plasmas. The HES approach avoids treatments of cross-diffusion terms which cause numerical instabilities in conventional approaches using an elliptic equation (EE). A test calculation reveals that the HES approach can robustly solve problems of strong magnetic confinement by using an upwind method. The computation time of the HES approach is compared with that of the EE approach in terms of the size of the problem and the strength of magnetic confinement. The results indicate that the HES approach can be used to solve problems in a simple structured mesh without increasing computational time compared to the EE approach and that it features fast convergence in conditions of strong magnetic confinement.

A flux-splitting method for hyperbolic-equation system of magnetized electron fluids in quasi-neutral plasmas

A flux-splitting method is proposed for the hyperbolic-equation system (HES) of magnetized electron fluids in quasi-neutral plasmas. The numerical fluxes are split into four categories, which are computed by using an upwind method which incorporates a flux-vector splitting (FVS) and advection upstream splitting method (AUSM). The method is applied to a test calculation condition of uniformly distributed and angled magnetic lines of force. All of the pseudo-time advancement terms converge monotonically and the conservation laws are strictly satisfied in the steady state. The calculation results are compared with those computed by using the elliptic-parabolic-equation system (EPES) approach using a magnetic-field-aligned mesh (MFAM). Both qualitative and quantitative comparisons yield good agreements of results, indicating that the HES approach with the flux-splitting method attains a high computational accuracy.

Evaluation of discharge behavior of the pulsed plasma thruster SIMP-LEX

The pulsed plasma thruster Add Simp-lex, developed at the IRS, was investigated at the University of Tokyo to further characterize the thruster’s performance and discharge behavior. This was done by experimental investigation of configurations with a different amount of capacitors and discrete applied voltages. To do so, a measurement system for the discharge current and the optical properties was built up and successfully applied. Further, the numerical model for the prediction of the current-normalized magnetic flux density was improved and the convergence properties of the integration towards the change in inductance studied. From the discharge current waveforms and the pictures taken from the propagating plasma, information about the amount of plasma creations, their propagation velocity and the oscillation behavior was deducted. For further characterization, the energy transfer efficiency and the electrical efficiency was derived from these data, leading to a tool to compare different configurations. It was found, that a middle voltage yields higher electrical efficiencies of about 40% whereas the energy transfer efficiency is higher the lower the applied voltage.

Magnetized Electron Flow Calculation Using a Hyperbolic System

The hyperbolic-equation-system (HES) approach has been developed for the calculation of magnetized electron fluids in quasi-neutral plasmas. The HES approach has been applied to a particle-fluid hybrid modeling of a Hall thruster, to evaluate the applicability of the approach to practical simulations. The validity of the use of the HES approach is confirmed based on three aspects. First, the calculated thruster performance is in good agreement with the experimental results. Also, it is proven that the two-dimensional conservation law of the electron flow is strictly computed with the HES approach. Lastly, the Boltzmann relation along magnetic lines of force is confirmed, which indicates the effect of magnetic confinement is accurately calculated.

UNISEC-Global challenge: How can UNISEC-Global contribute to long term sustainability of space activities?

Long term sustainability is vital to the future space activities. This is a key theme of the discussions in global space forums such as UNCOPUOS. UNISEC in Japan and UNISEC-Global has been facilitating practical space engineering education using nano-satellites. The issues of increasing density of debris in orbit and limited resources of radio frequencies are very relevant to nano-satellite activities at university level. In this paper, firstly UNISEC-Global is introduced, secondly, the concept of space sustainablity is described. Thirdly, UNISEC-Globals contribution to improving awareness of space sustainability among universities across the world is described, and fourthly, innovative technological approaches which may assist in the solution to these problems are introduced, followed by a discussion on the role of UNISEC-Global initiatives in this field.

Numerical analysis of azimuthal rotating spokes in a crossed-field discharge plasma

Low-frequency rotating spokes are obtained in a cross-field discharge plasma using two-dimensional numerical simulations. A particle-fluid hybrid model is used to model the plasma flow in a configuration similar to a Hall thruster. It has been reported that the drift-diffusion approximation for an electron fluid results in an ill-conditioned matrix when solving for the potential because of the differences in the electron mobilities across the magnetic field and in the direction of the E

High-order upwind and non-oscillatory approach for steady state diffusion, advection–diffusion and application to magnetized electrons

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Contribution of UNISEC-global to capacity building in space engineering

B drift. In this paper, we employ a hyperbolic approach that enables stable calculation, namely, better iterative convergence of the electron fluid model. Our simulation results show a coherent rotating structure propagating in the E

Modeling of Electron Fluids in Hall Thrusters Using a Hyperbolic System

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Effect of thruster scaling on pre-sheath and ion-loss region in Hall thrusters

B direction with a phase velocity of 2,500 m/s, which agrees with experimental data. The phase velocity obtained from the numerical simulations shows good agreement with that predicted by the dispersion relation of the gradient drift instability.