Nobuki Kawashima

Space Plasma Physics Space Experiments with Particle Accelerators

Electron and plasma beams and neutral gas plumes were injected into the space environment by instruments on Spacelab 1, and various diagnostic measurements including television camera observations were performed. The results yield information on vehicle charging and neutralization, beam-plasma interactions, and ionization enhancement by neutral beam injection.

Vehicle charging observed in SEPAC Spacelab-1 experiment

Electrostatic charging of the orbiter has been studied by the Space Shuttle/Spacelab-1 using the Space Experiments with Particle Accelerators (SEPAC). Charging of the orbiter due to electron beam emission has been analyzed using data from a Langmuir probe, floating probes, an electron energy analyzer and a low-light-level TV camera. Charging of the orbiter is found to be strongly dependent upon the attitude of the orbiter with respect to the velocity vector. The orbiter potential has reached the beam acceleration voltage well beyond one kilovolt, which is much higher than that previously observed in electron beam experiments on sounding rockets in the lower ionosphere.

Results from a series of tethered rocket experiments

The data obtained in the most recent Japan-US tether rocket experiment CHARGE 2 have been further analyzed. The interaction of the moving tether system across the geomagnetic field with the ionospheric plasma can be explained by a simple model of the current through a plasma. The response of the tether system when a high voltage is applied is studied and 500 volts could be applied without any appreciable discharge. The detected signal of the wave excited by an application of high voltage between the mother and daughter rocket and by a pulse modulated electron beam is also studied.

Neutralization of Beam-Emitting Spacecraft by Plasma Injection

An impulsive plasma injection has been used to study charge neutralization of the Space Shuttle Orbiter while it was emitting an electron beam into space. This investigation was performed by Space Experiments with Particle Accelerators on Spacelab-1. A plasma consisting of 10 to the 19th argon ion-electron pairs was injected into space for 1 ms while an electron beam was also being emitted into space. The electron beam energy and current were as high as 5 keV and 300 mA. While the orbiter potential was positive before the plasma injection and began to decrease during the plasma injection, it was near zero for 6 to 20 ms after the plasma injection. The recovery time to the initial level of charging varied from 10 to 100 ms. In a laboratory test in a large space chamber using the same flight hardware, the neutralization time was 8-17 ms and the recovery time was 11-20 ms. The long duration of the neutralization effect in space can be explained by a model of diffusion of the cold plasma which is produced near the Orbiter by charge exchange between the neutral argon atoms and the energetic argon ions during plasma injection.

Artificial auroras in the upper atmosphere 1. Electron beam injections

Artificial electron beams from the Space Experiments with Particle Accelerators (SEPAC) on the ATLAS 1 Spacelab payload were used to stimulate auroral emissions at southern auroral latitudes. The emitted electron beams were monoenergetic at 6.25 keV and were fired in one-second pulses every fifteen seconds with currents of 1.21 A. Optical measurements of the beam were made in the vicinity of the Shuttle Orbiter by its on-board television camera and in the upper atmosphere by the Atmospheric Emissions Photometric Imager (AEPI). AEPI imaged auroral emissions in both white light and at the 427.8 nm N2+ emission line. Energy deposition calculations and the results of previous sounding-rocket experiments had suggested that emissions with scale sizes of about 130 meters would result from the artificial electron beams with the visible emissions extending from about 110 to 130 km altitudes. In the ATLAS 1 experiments the auroral imaging was performed from the Shuttle, providing a new perspective on the artificial auroras and allowing the emissions to be traced from altitudes near the 295 km Shuttle altitude down to the 110 km level along the curved magnetic field lines.

Rail gun experiment (HYPAC) at ISAS (meteorite impact simulation)

A railgun for the study of the interaction of meteorites with planetary surfaces and the interaction of space debris was developed. The authors have attained a velocity constantly higher than 5 km/s, with a maximum of 6 km/s. The importance of plasma confinement behind the projectile to prevent a leakage is shown to realize a high velocity. An effective acceleration using an aluminum rail is also shown. >

Laser Energy Transmission for a Wireless Energy Supply to Robots

The robot development is actively done as a very hopeful tool in many disciplines, however, right now, the robot is not used actually for practical use. It is clear that once it is actually used, it becomes very important how to keep supplying energy. The wireless energy supply is mandatory. In most cases, it is considered that the rechargeable battery is most easy to solve it, however, for example, in nuclear power plant accident or chemical weapon disaster due to terrorism, once the robot enters into the contaminated area, it is almost impossible to return for the battery recharging. The wireless energy transmission is mandatory. Even for those robots working in the area where it is impossible or very difficult for a man to access but the robot can return for the refueling, the wireless energy transmission is required when, for example, the robot malfunctions and can not return. A long time operation is required for the trouble shooting and for repair. Moreover, some important activities urgently needed may not allow the robot to return for the refueling, then the wireless energy transmission is also very useful. To realize the wireless energy supply, either the microwave or the laser energy transmission is considered most hopeful. The microwave energy transmission has an advantage of higher energy conversion efficiency and can be used through the cloud, but it is not easy to concentrate the power in a small region. It is considered as a useful tool for the power transmission from the space power station (SPS) to the earth. Laser is easy to focus the beam in a small area and the mirror can be used to transmit energy behind a blind corner. Due to the development of laser diodes (LD), a very compact laser transmitter system can be constructed. For the robot use, the laser is more advantageous over the microwave system.

Space Experiments with Particle Accelerators (SEPAC)

Space Experiments with Particle Accelerators (SEPAC) is a project of performing an active experiment on the Spacelab 1 in 1983 using electron and plasma beams injected into space plasma. General description, present status and future program are described.

Measurements of Vehicle Potential Using a Mother-Daughter Tethered Rocket

When plans were being made in 1969 to perform the first electron beam experiment in space a question was raised concerning the amount of neutralization current which could be collected from the ambient ionospheric plasma when a beam of electrons was emitted from an isolated vehicle such as a sounding rocket or satellite. Although the first such experiment was a success and more than 20 similar flights have been made since that time the original question of the amount of neutralization current available from the ambient ionospheric plasma is still unanswered.

VLF Wave Experiments in Space Using a Modulated Electron Beam

A sounding-rocket payload to study the generation and emission of electromagnetic waves from a modulated electron beam was developed and successfully flown from the Poker Flat Research Range, Alaska, in March 1992 on a Black Brant 11 sounding rocket. We describe the mission objectives, the instrumentation, flight operations, and preliminary results from the flight. The payload contained a modulated electron gun with a triode arrangement of electrodes allowing modulation of the beam current up to vlf frequencies. Vehicle charging was inhibited by a gas-release system, synchronized with the beam emissions. A network of ground stations was set up to try to receive signals from the modulated beam, and low-light systems were set up to look for evidence of the beam below the payload trajectory. No evidence of beam-induced wave radiation to the ground was detected. However, strong vlf frequencies following the preset program were clearly detected by the diagnostic free flyer and the tethered daughter payload segment. The effect of the gas releases was very marked. The vehicle potential dropped from over 1 kV to about 30 V when the gas was turned on. Some evidence of the light from beam-atmosphere interactions was seen near the end of the flight, but in general, the optical results were not very informative. The launch was successful, mission operations were as planned, and good-quality onboard data were collected throughout the operational part of the flight.