Magnetoplasmadynamic Arcjet Research Articles

Ground Tests and Space Tests of a Magnetoplasmadynamic Arcjet Thruster System

Ground Tests and Space Tests of a Magnetoplasmadynamic Arcjet Thruster System

Research and Development of Magnetoplasmadynamic Arcjets for Future High-Power Space Applications

Research and Development of Magnetoplasmadynamic Arcjets for Future High-Power Space Applications

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 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) 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/f <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.6</sup> (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.

準定常MPDアークジェットプルームの非定常特性

The plasma plume of a 1-MW-class quasi-steady magnetoplasmadynamic (MPD) arcjet is studied to reveal the plume plasma fluctuations in a downstream plume region (150–900mm away from the MPD arcjet). By using a double probe and a time-of-flight method, the averaged velocity distribution along the centerline of the plasma plume is found to be almost constant (∼38km/s), and the average ion saturation current is inversely proportional to the square of the distance from the MPD arcjet. The power spectrum density (PSD) of the ion saturation current is proportional to 1/f 1.6 (f : frequency) in 50–200kHz range and it is proportional to 1/f 2.6 above 200kHz. However, fluctuations are dominant in the lower frequency region of 50kHz, where PSD vs. f curve is flat. The spectrum analysis of the fluctuations shows that the MPD arcjet plume in the downstream region is isotropic turbulent flow.

Thrust Measurement of Pure Magnetic Sail

A Pure Magnetic Sail is a deep space propulsion system consisting of a coil mounted on a spacecraft. In order to predict the thrust characteristics of a Pure Magnetic Sail in space, thrust measurement and magnetic field measurement were conducted using a scale model in a laboratory. To simulate the solar wind, a magnetoplasmadynamic arcjet provides a high density (2×1019 m-3) and high velocity (47 km/s) plasma flow that impinges on a 20-turn 25-mm-radius coil simulating a Pure Magnetic Sail. When the magnetic cavity size of the scale model (L) is increased from 0.12 to 0.17 m, the thrust increases from 0.47 to 0.92 N. Scaling up, this experiment corresponds to a 300-km diameter Pure Magnetic Sail in space. The thrust also depends on the coil tilt angle, which is the angle between the direction of the solar wind flow and the coil axis. The maximum thrust of 1.5 N is obtained for a tilt angle of 90 degrees.

Characteristics of electromagnetically accelerated plasma flow in an externally applied magnetic field

In order to clarify the acceleration mechanism of applied-field magneto-plasma-dynamic arcjet (MPDA) plasma, the spatial profiles of the flow field and electromagnetic field near the outlet of the MPDA were measured using magnetic probes and the spectroscopic method. The plasma current densities and Lorentz forces acting on the plasma were evaluated experimentally. It was found that the azimuthal rotation of the exhausted plasma in the applied magnetic field is determined by a balance among the E×B drift, the diamagnetic drift, and the centrifugal force drift. Three components of the Lorentz force, i.e., the radial, the azimuthal, and the axial, were measured experimentally for the first time. The radial component Fr was dominant among the three components and the axial one (Fz) was weakened by the deceleration force, which spontaneously appeared in the applied-field MPDA plasma due to a diamagnetic effect of the high-beta plasma. It was demonstrated that the deceleration force can be converted to an acceleration force in an externally applied diverging field.

Generation of supersonic plasma flows using an applied-field MPD arcjet and ICRF heating

A quasi-steady, supersonic plasma flow was produced by using a magneto-plasma-dynamic arcjet (MPDA) in a divergent magnetic nozzle. The ion acoustic Mach number, Mi, evaluated by spectroscopy and Mach probe measurement, was unity in the uniform field near the MPDA and reached almost 3 in the divergent magnetic nozzle. In the case of a subsonic flow near the exit of the MPDA, a magnetic Laval nozzle was effective in converting it to a supersonic flow with Mi = 1 at the throat. We heated ions of the fast-flowing plasma by ICRF (ion-cyclotron-range of frequency) in a magnetic beach field. The increased thermal energy was converted to flow energy as it passed through the divergent magnetic nozzle in accordance with the constant magnetic moment. We were able to successfully control the plasma flow with a wide range of densities for basic magnetohydrodynamic (MHD) studies and space thruster applications.

Measurement of Flow Velocity of MPD Arcjet in GAMMA 10

At both end cells of GAMMA 10, two of Magneto-Plasma-Dynamic Arcjet (MPDA) are installed. MPDAs consists of two coaxial electrodes (tungsten stick and molybdic cylinder), and can produce quasi-stationary hydrogen plasmas. In GAMMA 10, the plasma generated by the MPDAs are used as the seed plasma. The main plasma is produced by ion cyclotron range of frequency (ICRF) waves in combination with the hydrogen gas injection. In the center at r=0 near the mirror throat of plug/barrier cell, the flow velocity and the mach number are measured with a mach probe in cases of several discharge voltages. The flow velocity and the mach number increase with the discharge voltage. The mach number of the seed plasma and the main plasma (from the confined region) is also measured in the radial direction. The flow velocity and the mach number of the seed plasma become small in the core region than in the peripheral region.

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.

A Multi-Reflection Type Visible-Laser Interferometer for High Density Plasma Measurements

In order to measure a high density plasma more than 1020 m-3 in the vicinity of a magneto-plasma-dynamic arcjet (MPDA), a visible-laser interferometer is fabricated using a He-Ne laser (λ = 632.8 nm). As it doesn't have enough phase shift when the light passes through the MPDA plasma once, we adopt a multi-reflection optical system in this interferometer to improve the phase sensitivity. We measured a plasma density by the interferometer and estimated the maximum value of line-integrated density of 4 × 1019 m-2 . These experimental results are consistent with that of electrostatic probe measurement in the downstream region.

Laboratory Experiment of Plasma Flow Around Magnetic Sail

To propel a spacecraft in the direction leaving the Sun, a magnetic sail (MagSail) blocks the hypersonic solar wind plasma flow by an artificial magnetic field. In order to simulate the interaction between the solar wind and the artificially deployed magnetic field produced around a magnetic sail spacecraft, a laboratory simulator was designed and constructed inside a space chamber. As a solar wind simulator, a high-power magnetoplasmadynamic arcjet is operated in a quasisteady mode of 0.8 ms duration. It can generate a simulated solar wind that is a high-speed (above 20 km/s), high-density (1018 m−3) hydrogen plasma plume of ∼0.7 m in diameter. A small coil (2 cm in diameter), which is to simulate a magnetic sail spacecraft and can obtain 1.9-T magnetic field strength at its center, was immersed inside the simulated solar wind. Using these devices, the formation of a magnetic cavity (∼8 cm in radius) was observed around the coil, which indicates successful simulation of the plasma flow of a MagSail in the laboratory.

Laser Absorption Velocimetry of Plasma Flow in Two-Dimensional Magnetoplasmadynamic Arcjet

Experimental velocimetry in the discharge chamber of a two-dimensional magnetoplasmadynamic (MPD) arcjet, fabricated for experimental internal flow measurement, was conducted to investigate the acceleration process for hydrogen propellant. In the experiment, we evaluated the neutral atom velocity and the temperature from the laser absorption spectroscopy using a tunable diode laser. The results using two types of anode, a flared-type anode and a converging-diverging (C-D)-type anode, were compared for the case with a discharge current of 13 kA and a mass-flow rate of 0.65 g/s. It was found that a large velocity slip between the ions and the neutrals prevented the acceleration of the neutral particles. This velocity slip is expected to reduce thrust performance because the flow with ion-neutral slip requires additional electric power compared to the flow without velocity slip. The velocity slip was reduced in the case of the C-D anode compared to the flared anode because of strong ion-neutral momentum coupling in the throat region of the C-D anode.

Mach Probe Measurements in Unmagnetized Plasmas with Subsonicand Supersonic Flow

AbstractCharacteristics of an up‐down type Mach probe are investigated by using a directional Langmuir probe (DLP) in unmagnetized plasmas with subsonic and supersonic flow produced by a magneto‐plasma‐dynamic arcjet (MPDA). The ion acoustic Mach number Mi is derived from plasma flow velocity Up and ion temperature Ti measured by spectroscopy and electron temperature Te by Langmuir probe. The obtained values of Mi are compared to the DLP data in various conditions of plasma flow and the coefficient of Mc in the Mach probe formula,Mi = Mc ln(Jup/Jdown ) , is evaluated. The obtained data are also compared with Hutchinson's PIC simulation results in an unmagnetized plasma and are in good agreement with each other. The dependence of ln(Jup/Jdown ) on cosϕ can be expressed as a quadratic function under subsonic (Mi &lt; 1) and supersonic (Mi &gt; 1) flow, so that the up‐down type Mach probe can detect the components of plasma flow vector even when the probe collection surface inclines to plasma flow direction. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

磁気セイルシミュレータの開発

In order to simulate the interaction between the solar wind and the artificially deployed magnetic field produced around a magnetic sail spacecraft, a laboratory simulator was designed and constructed inside the space chamber (2m in diameter) at ISAS. As a solar wind simulator, a high-power magnetoplasmadynamic arcjet is operated in a quasisteady mode of ∼0.8ms duration. It can generate a simulated solar wind flow that is a high-speed (above 20km/s), high-density (above 1017m-3) hydrogen plasma plume of ∼70cm in diameter. A small coil (18mm in diameter), which is to simulate a magnetic sail spacecraft and can obtain 1.9-T magnetic field strength at its center, was immersed inside the simulated solar wind. Using these devices, the formation of a magnetic cavity (∼8cm in radius) was observed around the coil, which indicates successful simulation of the plasma flow around the coil (simulated magnetic sail spacecraft) in the laboratory.

Evaluation of Mach probe characteristics and measurement of high-Mach-number plasma flow

Mach probe characteristics are evaluated by using a directional Langmuir probe (DLP) in a fast flowing plasma produced by a magneto-plasma-dynamic arcjet (MPDA). The obtained data are compared with Hutchinson's simulation results which are calculated using a particle-in-cell (PIC) code in an unmagnetized plasma [I.H. Hutchinson, Plasma Phys. Control. Fusion, 44 (2002) 1953]. The experimentally obtained data are in good agreement with the simulation results in the wide range of M i (0.4 < M i < 1.7). Two types of the Mach probe, where the probe tips are facing to up–down directions and para–perp ones, are compared with model formulas and the simulation results. Good agreements are obtained among these data and calibration factors to determine the Mach number are evaluated.

Large applications of electromagnetically accelerated plasma to material spraying

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Two types of MPD arcjet generator were developed for applications to mullite, zirconia, titanium nitride and silicon nitride sprayings. The MPD spray process could successfully form dense, uniform and hard ceramic coatings. In titanium nitride reactive spraying, plasma diagnostic measurement and flowfield calculation were also carried out. A large amount of N and N + was expected to be exhausted with a high velocity from the MPD generator. Both the electron temperature and the electron number density were kept high at a substrate position compared with those for conventional low-pressure thermal sprayings. A chemically active plasma with excited particles of N +, Ti, Ti + and Ti 2+ was considered to contribute to better titanium nitride coatings. All coating characteristics showed that the MPD arcjet generators had high potentials for ceramic spraying.

Improvement of Flow Characteristics for an Advanced Plasma Thruster

A higher specific impulse and a larger thrust are required for a manned interplanetary space thruster. Until the realization of a fusion-plasma thruster, a magneto-plasma-dynamic arcjet (MPDA) powered by a fission reactor is one of the promising candidates for a manned Mars space thruster. The MPDA plasma is accelerated axially by a self-induced j × B force. Thrust performance of the MPDA is expected to increase by applying a magnetic nozzle instead of a solid nozzle. In order to get a much higher thruster performance, two methods have been investigated in the HITOP device, Tohoku University. One is to use a magnetic Laval nozzle in the vicinity of the MPDA muzzle for converting the high ion thermal energy to the axial flow energy. The other is to heat ions by use of an ICRF antenna in the divergent magnetic nozzle. It is found that by use of a small-sized Laval-type magnetic nozzle, the subsonic flow near the muzzle is converted to be supersonic through the magnetic Laval nozzle. A fast-flowing plasma is successfully heated by use of an ICRF antenna in the magnetic beach configuration.

２次元型ＭＰＤアークジェットの速度場と電力収支計測

Velocity and temperature measurements were conducted for a two-dimensional magnetoplasmadynamic arcjet with hydrogen propellant. To obtain the velocities of both atoms and ions, laser absorption spectroscopy was employed for atom, and time-of-flight technique was used for ions. In a quasi-steady operation at 13kA/0.65g/s, larger ions velocity (33km/s) than that of the atoms (13km/s) was found in the case of flared anode configuration, which implies that large mean free path between the ions and atoms prohibited momentum transfer from the ions to the neutral particles. This velocity difference was not observed in the case of converging-diverging anode, where the high-density plasma inside the discharge chamber enhances momentum transfer from ions to atoms. In addition to the velocity difference, diagnostics by probe methods revealed high ion temperature in comparison with that of electrons at the thruster exit. Using the velocities and temperatures together with the densities of each particle, energy flux of the magnetoplasmadynamic arcjet was discussed. The large energy deposition into thermal and internal energy modes near the thruster exit indicated a large amount of pressure energy that should be converted to velocity energy by an appropriate nozzle design to further improve the thrust performance.

Evaluation of Para-Perp Type Mach Probe by Using a Fast Flowing Plasma

Mach probe with two collecting tips facing to the direction parallel and perpendicular to the plasma fl ow, named para-perp type one, is evaluated by using a directional Langmuir probe (DLP) in a fast fl owing plasma produced by an MPD (Magneto-Plasma-Dynamic) arcjet. We present simple formulas to determine an ion acoustic Mach number Mi from the ratio of collected ion saturation currents. The formulas and experimentally-obtained data are compared with Hutchinson’s simulation results which are calculated using a particle-in-cell(PIC) code in an unmagnetized plasma condition. [I.H. Hutchinson, Plasma Phys. Control. Fusion, 44 1953 (2002).] Good agreements are obtained among these data in both subsonic and supersonic plasma fl ows. Correction factor κ to determine Mi is presented under various conditions of Ti/Te and the specifi c heat ratio for ions γ i.

電磁加速プラズマを用いた窒化珪素の高速成膜

In magneto-plasma-dynamic (MPD) arcjet generators, plasma is accelerated by electromagnetic body forces. Silicon nitride reactive deposition was carried out using an MPD arcjet generator with crystal silicon rods and nitrogen gas. Because the MPD arcjet generator produces higher-velocity, higher-temperature, higher-density and larger-area plasmas than those with conventional thermal plasma torches, nitriding of silicon can be enhanced. A dense and uniform β-Si3N4 film of 30μm in thicknes was formed after 200 shots at a repetitive frequency of 0.05 Hz with a discharge current of 9 kA and a substrate temperature of 700 °C. The Vickers hardness reached about 1300. It was found that film thickness was highly sensitive to discharge current and that microstructure of the film was sensitive to the substrate temperature. These results show that the MPD arcjet generator has high potentials for silicon nitride deposition.