Kazuma Ueno

Hybrid Particle-in-Cell Simulations of Magnetic Sail in Laboratory Experiment

Magnetic sail is a propellantless propulsion system proposed for an interplanetary space flight. The propulsive force is produced by the interaction between the magnetic field artificially generated by a hoop coil equipped with the magnetic sail and the solar wind. Three-dimensional hybrid particle-in-cell simulations are performed to elucidate the plasma flow structure around the magnetic sail and to measure the propulsive force of the magnetic sail. We report the characteristics of the magnetosphere, such as the profile of the magnetic field, the thickness of the magnetopause current layer, and the predicted thrust value obtained by simulations, which agree well with laboratory experiment when simulations are carried out by considering the ion-neutral collision effect. The hybrid particle-in-cell simulation carried out without considering the collisional effect gave a thrust value of 3.5 N, which can be applied to the thrust evaluation of the magnetic sail in a magnetosphere with size of 300 km in a collisionless interplanetary space.

Experimental Simulation of Magnetic Sails

In order to simulate the interaction between the artificially deployed magnetic field produced around a magnetic sail spacecraft and the solar wind, a laboratory simulator in a space chamber was designed. As a solar wind simulator, a high-power magnetoplasmadynamic arcjet was operated in a quasisteady mode of about 0.8 ms duration to provide a high-speed hydrogen plasma plume of about 0.7 m in diameter, which is accelerated to above 20 km/s with high plasma densities around 10 17 -10 19 m -3 . Into this high- density and high-velocity plasma jet, a small coil of 2-cm-diameter was immersed to obtain 1.9-T magnetic field at the center of the coil. These devices are operation in a large 2-m- diameter space chamber, and the formation of a magnetic cavity was observed around the coil. From the analysis of scaling parameters, it is found that the laboratory experiment of the plasma flow around the coil of the magnetic sail corresponds to a sub-Newton-class magnetic sail.

Interaction between plasma flow and magnetic field in scale model experiment of magnetic sail

Magnetic sail (MagSail) is a next-generation deep space propulsion system, which uses the energy of the solar wind. The MagSail produces an artificial magnetic field and captures the energy of the solar wind plasma to propell a spacecraft in the direction of the solar wind. In order to conduct a scale-model experiment of the plasma flow of a MagSail, we developed a solar wind simulator based on a magnetoplasmadynamic arcjet, which obtained a high density (˜1018 m-3) and high velocity (˜60 km/s) plasma flow in a quasi-steady mode of about 1 ms duration. Based on scaling considerations, a solenoidal coil (18 mm in diameter and the magnetic flux density at the coil center ˜ 1.9 T) was designed and was immersed into the plasma flow. A magnetic cavity, which is very similar to that of the geomagnetic field, was observed, although the magnetic cavity of MagSail is usually much smaller than the geomagnetic cavity of the Earth.

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.

Plume Characteristics of a Quasi-Steady Magnetoplasmadynamic Arcjet

The plasma plume of a 1-MW-class quasi-steady magnetoplasmadynamic (MPD) arcjet is studied to determine the plume structure and plasma plume fluctuations in a downstream plume region (250-1250 mm away from the MPD arcjet). By using a double probe and a high-electron-temperature ( ~ 5 eV) and high-number-density (~8 ×1019 m-3) region, so-called “cathode jets” are found along the central axis of plasma plume close to the MPD arcjet. Moreover, the plasma plume radial profile is constant in a downstream plume region (≥ 750 mm from the MPD arcjet). The power spectrum density (PSD) of the ion saturation current is proportional to 1/f1.6 (f: frequency) for f >; 80 kHz, and in this frequency range, PSD decreased with distance from the MPD arcjet. In contrast, in the frequency region <; 80 kHz, the PSD-f curve is at a constant value. Although a peak in the discharge voltage is attributed to the generalized lower hybrid drift instability (GLHDI), this instability is not found in the plasma plume near the MPD arcjet. The influence of the GLHDI is limited only to the discharge chamber, and fluctuations caused by the instability are random in the downstream region.

Scale-model Experiment of Magnetoplasma Sail for Future Deep Space Missions

When Magnetic sail (MagSail) spacecraft is operated in space, the supersonic solar wind plasma flow is blocked by an artificially produced magnetic cavity to accelerate the spacecraft in the direction leaving the Sun. To evaluate the momentum transferring process from the solar wind to the coil onboard the MagSail spacecraft, we arranged a laboratory experiment of MagSail spacecraft. Based on scaling considerations, a solenoidal coil was immersed into the plasma flow from a magnetoplasmadynamic arcjet in a quasi‐steady mode of about 1 ms duration. In this setup, it is confirmed that a magnetic cavity, which is similar to that of the geomagnetic field, was formed around the coil to produce thrust in the ion Larmor scale interaction. Also, the controllability of magnetic cavity size by a plasma jet from inside the coil of MagSail is demonstrated, although the thrust characteristic of the MagSail with plasma jet, which is so called plasma sail, is to be clarified in our next step.

Scale-Model Experiment of Magnetoplasma Sail : Preliminary Results

** Magnetic sail (MagSail) is a deep space propulsion system, which uses the energy of the solar wind. MagSail produces an artificial magnetic field and captures the energy of the solar wind plasma to propel a spacecraft in the direction of the solar wind. In order to conduct a scale-model experiment of the plasma flow of a MagSail, we developed a solar wind simulator based on a magnetoplasmadynamic arcjet in a quasi-steady mode of about 1 ms duration. Based on scaling considerations, a solenoidal coil was designed and it was immersed into the plasma flow. In this setup, a magnetic cavity, which is similar to that of the geomagnetic field, was observed, although the magnetic cavity of MagSail is usually much smaller than the geomagnetic cavity of the Earth. It was experimentally confirmed that MagSail could produce thrust even in such ion Larmor scale. Also, an extension of this MagSail experiment to MagSail with plasma jet (M2P2 or MPS) is in progress, and some preliminary results are reported.

Experimental Investigation of Magnetoplasma Sail with High Beta Plasma Jet

Magnetoplasma Sail (MPS) is one of the next generation in-space propulsion systems that utilize the interaction between the solar wind and the magnetosphere inflated by the plasma injection around a spacecraft. An important issue of MPS is thrust increase by the plasma injection. Experimental validation of the thrust characteristics is very important before applying the idea of the thrust increase by the plasma injection to realistic spacecraft design. In order to conduct a scale model MPS experiment, a laboratory simulator was designed and constructed inside the space chamber (2 m in diameter). As a solar wind simulator, a triple magnetoplasmadynamic arcjet generates a high-speed (>20 km/s), high-density (>10m) hydrogen plasma jet of 0.8 ms duration. A small coil (76 mm in a diameter) and Mini-MPD arcjet as a MPS simulator was immersed inside the simulated solar wind. The thrust characteristics of MPS with plasma injection have been experimentally investigated as a function of the magnetic moment M and the dynamic pressure of the injected plasma Pinf. The thrust gain is growing both with βk value which is ratio of the dynamic pressure of the injection plasma to the magnetic pressure, but the thrust saturation was observed at the high βk condition at the injection point (βk~1). The maximum thrust gain in this paper which is the ratio between the thrust with plasma injection and the thrust without plasma injection was about 4.1.

Experimental Simulation of Magnetoplasma Sail for Thrust Measurement

Magnetoplasma Sail (MPS) is one of the sail propulsion system using the solar wind and suitable for deep space exploration. MPS uses an artificial magnetic field for capturing the solar wind, which is generated by a combination of a coil and a plasma injection. In order to measure thrust of a miniature MPS directory, a parallelogram-pendulum-type thrust stand was developed and installed on MPS ground simulator. In comparison with 0.6 N of Magnetic Sail thrust for 90 mm-magnetosphere, when the magnetospheric size for 115 mm was produced, 4.0 N thrust of the miniature MPS was obtained. The thrust value may include thrust originated with MPD arcjets used for magnetospheric inflation. Our next step of thrust measurement is evaluation of thrust increment for magnetospheric inflation.

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.