Kohnosuke Sato

Augmented railgun using a permanent magnet

The use of a permanent magnet instead of an electromagnet has been proposed for the augmentation of the magnetic field of a railgun driven by a current of approximately 20 kA. A permanent magnet has the following advantages in comparison with conventional augmentations using additional turns: (1) simple configuration of the system, (2) temporally and spatially constant magnetic fields, and (3) high efficiency. Here, the operation of a conventional railgun and that of an augmented railgun using a permanent magnet are compared experimentally, and the usefulness of the permanent magnet is described.

Railgun using plasma initiation separated from the projectile

Preacceleration of a projectile is important for reducing the erosion of the bore surface in a railgun. Gas guns, electrothermal guns, and other railguns are commonly used to preaccelerate the projectile. A new method, called the plasma initiation separated from the projectile (PISP) method is proposed, and its effectiveness is confirmed experimentally. A thin copper wire is placed near the edge of the railgun, and it explodes and forms a plasma that has a fast flow velocity due to the Lorentz force. This fast flowing plasma collides with the projectile, which obtains an initial velocity mainly by the momentum transfer. Since the current increases while only the plasma is accelerated, the driving force of the projectile just after the collision of the plasma with the projectile is large. The PISP method works as an inductive energy storage circuit with an opening switch. >

Spectroscopic measurements of railgun plasma armatures in an augmented railgun using a permanent magnet

Measurements of electron density using Stark broadening of the H/sub /spl alpha// line are performed to investigate the behavior of plasma armatures in rail guns with and without an augmenting magnetic field. A permanent magnet with a magnetic flux density of 1.25 T was used to augment the magnetic field of one railgun. Driving currents of 20 and 25 kA are supplied to the railguns with and without the augmenting magnetic field, respectively, in order to maintain the same peak Lorentz force on the projectile. Also a gradual temporal increase in electron density and length of the plasma armature is observed in the augmented railgun.

Electron Capture Cross Sections in High Energy He2++Li° Collisions

Single and double electron capture cross sections for He 2+ in collision with Li° have been measured in the energy range of 0.8–2.0 MeV. The lithium target density was absolutely determined by the Rutherford scattering measurement. The results are consistent with the recent data measured at lower energies.

Spindle-Cusp Confinement Properties of Laser-Produced Plasma in a Low-Beta Regime

Behavior of a spindle-cusp plasma produced at its central null-field point from a thin wire target by laser pulse is experimentally studied, mainly in a low plasma-beta regime, by means of many different plasma diagnostics. As the results, somewhat queer confinement properties have been found, and some considerations are given for the observed results.

Experimental and Theoretical Studies on Filling a Stel a Rator with Laser-Produced Plasma

Experiments have been performed on filling a stellarator with a noncurrent-carrying laser-produced plasma. Simultaneous plasma production by means of pulsed laser beams at four separate positions on the toroidal magnetic axis has been found to drastically enhance the trapping efficiency of produced plasma by stellarator field, to as high as 50 percent in contrast with about 10 percent in the case of plasma production at one position. This figure of 50 percent could be further improved to nearly 75 percent by spatially isotropic plasma productions which could not be realized in the present experiments owing to technical restrictions on the stellarator employed. The enhancement of trapping efficiency may be attributed to the reduction of toroidal plasma drift due to rotational transform coming into effect earlier in the multiposition production case. Some approximate theoretical analyses and considerations on toroidal drift motion of laser-produced plasma stream within stellarator field have also been presented, and the theoretical prediction on these analyses appears to be consistent with experimental results obtained.

Development of continuous pellet injector for Large Helical Device

Prototype continuous pellet injector has been designed and is under construction for the Large Helical Device at National Institute for Fusion Science in Japan. This injector is a centrifuge type, aiming at long-pulse pellet injection. A centrifuge pellet injector is a mechanical device that utilizes centrifugal force to accelerate solid hydrogen-isotope pellets using a high-speed rotating rotor. The injector consists of a hydrogen-isotope filament extruder, a pellet forming device, and a pellet accelerator. It is expected that pellets of 1 mm and 1.5 mm in diameter and length will be accelerated up to 800 m/sec in this system.

Characteristics of pellet injected discharges in TEXTOR

Pellets injected into the TEXTOR tokamak lead to a density profile peaking which is strongest at low plasma current and weakest at high current independent of BT. After the injection two types of density oscillations are excited, the first type follows immediately the injection and the second one is excited with a delay of more than ten milliseconds. The oscillations are also observed in runaway discharges; the synchrotron light from the relativistic electrons drops after the pellet injection and is subsequently modulated due to a trapping of the runaways in magnetic islands. First Faraday measurements have been performed indicating that the distribution of the plasma current is not measurably modified by the pellet.

Performance of a 1.5 m augmented railgun using a permanent magnet

A 1.5 m augmented railgun using a permanent magnet (ARGPM) has been assembled and tested. The goal of this work is to demonstrate fusion pellet injection with an extremely high velocity, in excess of 5 km/s. In this work, a wood fiber projectile is accelerated up to a velocity of 3.3 km/s in a plasma armature railgun without preaccelerators. Also, the velocity possible for a very light projectile accelerated by the ARGPM is discussed.

Fusion Product Diagnostics in Magnetic Confinement System

Fundamentals and present status of fusion product diagnostics in the case of magnetic confinement system are reviewed. Methods of diagnosing fusion products, i. e. neutrons and fast charged particles, are presented for DD, D3He and DT plasmas.