Haruya Kubo

Stable and reproducible production of high velocity projectile in ISAS railgun (HYPAC)

The ISAS (Institute of Space and Astronautical Science) railgun HYPAC (power supply: 6 mF, 10 kV, 300 kJ; rail: 13 mm phi *2 m bore) has been developed with a particular emphasis on stable and reproducible production of a high-velocity projectile so that it can actually be used for scientific impact experiments. A maximum velocity of 7.45 km/s has been obtained for a 0.87 g projectile in 4 mF, 288 kJ operation. The stability and reproducibility of HYPAC are so good that a velocity greater than 6 km/s can always be obtained with a prediction within +or-3% before the experiment. HYPAC is now extensively used for impact experiments for laboratory simulation in the field of planetary science. >

Interaction of plasma streams with a neutral gas cloud

Interaction of plasma streams with a neutral gas cloud was studied using gun-produced plasma and laser-produced plasma. The interaction of a quiet plasma stream shows a stable normal shock structure, but that of a plasma stream having turbulent magnetic fields shows a very complicated structure which resembles the ray structure of the type-i comet tail. From time resolved photographs of the interaction of the quiet plasma stream, one can obtain valuable information on the process of the growth of shock waves, and the experimental results are explained in terms of the snowplow model. Similarity relation concerning the type-i comet tail is also discussed.

Development of an induction type railgun

The remarkable feature of the induction type railgun is to enhance a plasma armature by transferring some part of a secondary arc current with an induction effect during the process of accelerating a projectile. Since the last conference we have built a new experimental system including an improved induction type railgun and a capacitor bank of a higher stored energy. This paper describes the experimental results obtained by the new experimental system. We performed the experiments both in a conventional railgun mode and an induction type railgun mode to compare their results. Not only an increase of the projectile velocity but also a reduction of the elongation of the plasma armature was observed in the induction type railgun mode. The projectile velocity increased from 2.4 km/s to 2.7 km/s, and the length of the plasma armature decreased from 26 cm to 20 cm.

IONIZATION MECHANISM AND EXCITATION TRANSFER IN THE PLASMA STREAM NEUTRAL GAS CLOUD INTERACTION

Ionization phenomena in a spatilly isolated neutral gas clod interacting with a gun-produced plasma stream was studied using an optical spectrometer, a Kerr cell camera and an image converter camera. Helium gas cloud is ionized by hydrogen or helium plasma stream, but not ionized by nitrogen or argon plasma stream. It is revealed that a neutral gas cloud is ionized by electrons heated in a shock wave created in the mutual gas cloud-plasma stream interaction. Observing H in the interaction of hydrogen plasma stream with various gas clouds, the intensity of H is the strongest when hydrogen plasma stream interacts with helium gas cloud. This is explained by excitation transfer.