Sadao Maeda

Compact pulsed power generator using an inductive energy storage system with two-staged opening switches

The pulsed power generator, named ASO-I, is extremely compact and light in comparison with a conventional pulsed power generator, which consists of a Marx bank and a water pulse forming line. The ASO-I has a two-staged opening switch, consisting of fuses in water and a plasma erosion opening switch, and can be operated hundreds of times a day at an output power of 230 kV and 35 kA. The parallel fuses are effective for power multiplication, and small differences in length of the parallel fuses do not influence the output power. The risetime of current through the short-circuit load decreases with the increase of the gap length of the spark gap, which is placed between the fuses and the load. The plasma erosion opening switch can be operated as a second opening switch, and the risetime of the current through the short-circuit load decreases from 250 to 10 ns. The maximum resistance of the plasma erosion opening switch is 3.5 Omega with an open-circuit load. >

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. >

Plasma properties and thin‐film formation in a pulsed electromagnetic inductive silane discharge

A new approach to prepare thin films in a pulsed inductive silane discharge is attemped. The time‐resolved spectral lines qualitatively clarified dynamics of decomposition process in the pulsed silane discharge and the local thermodynamic equilibrium in this discharge was investigated by the population density distribution estimated from excitation temperature measurement. The films had peculiar deposition patterns with good adhesion due to electromagnetic effects and main group of infrared spectra was the SiH3 complex.

Diamondlike carbon film deposition using a reactive pulsed electromagnetic inductive plasma process

A reactive pulsed electromagnetic inductive plasma process has been developed and used to deposit amorphous carbon films in methane discharges. The plasma state was investigated by analyzing spectral intensity emitted from H atoms and molecular fragments CH, which were produced by methane dissociation. The films deposited with this technique have outstanding characteristics due to the magnetohydrodynamic effect, good adhesion to room‐temperature substrates, wide optical gap, highly insulating, and diamondlike structure. The film properties are correlated with excitation temperature and intensity ratio between specified spectral lines. Furthermore, it is shown that a pulsed plasma process combined with an rf glow discharge deposits amorphous carbon films that contain crystalline particles.

Pulsed electromagnetic inductive plasma‐enhanced chemical‐vapor deposition of amorphous carbon films

A pulsed electromagnetic inductive methane discharge process was developed to form amorphous carbon thin films. In order to estimate the methane plasma state in the pulsed plasma process, the time‐resolved excitation temperature was measured by means of relative spectral intensity method. At the high electromagnetic compression phase the pulsed plasma has an excitation temperature of the same order (20 000–50 000 K) as in the conventional rf glow discharges. The deposited thin films are transparent in the IR and adhere well to room‐temperature substrates. The optical energy gap and the electrical conductivity of the amorphous carbon films are investigated and compared with the amorphous carbon films prepared with rf glow plasma chemical vapor deposition. The optical gap is observed to decrease from 1.26 to 1.14 eV as the deposition temperature and the charging voltage increase. It is shown that dynamic pulsed plasma flows affect the phase transition from a diamondlike structure to a graphitic structure.

PULSED POWER GENERATION FROM AN INDUCTIVE ENERGY STORAGE SYSTEM BY FUSES AND A PLASMA EROSION OPENING SWITCH.

The pulsed power generation from the inductive energy storage system, which is extremely compact and light, is investigated by the two-staged opening switches of fuses and a plasma erosion opening switch. The current rise time decreases from about 1 µs to about 200 ns by the fuses, and then to about 100 ns by the plasma erosion opening switch.

Plasma opening switch using laser-produced plasma

In order to construct a practical inductive energy storage pulsed power generator, the development of the opening switch which can repeatedly conduct a large current and then rapidly interrupt this current is necessary. Though the plasma opening switch (POS) can interrupt a large current rapidly, the effective number of switch operations is limited because of the decrease of the carbon sprayed on the insulator with each shot. We proposed a plasma opening switch using laserproduced plasma as one of opening switches which can be repeatedly used. The another advantage of the POS with the laser produced plasma is that it becomes possible to select more suitable plasma species for the operation of POS by changing the target materials. Here, the target materials are changed.

Compact pulsed power generator (aso-1) by an inductive energy storage system and its application to pulsed ion beams

The compact pulsed power generator of an inductive energy storage system is successfully constructed. Its pulsed power generator is named ASO-1. The copper fuses and the Plasma erosion opening switch are used as two-staged opening switches. The generation of pulsed ion beams is tried as one of applications of ASO-I. The pulsed ion beams are successfully generated by ASO-I.

New methods to reduce the erosion of bore in a small bore railgun

Erosion of the bore surface is a fatal problem for the repetitive operation of the railgun accelerators. Preaccelerators such as pneumatic guns, electrothermal guns and so on are generally used to reduce the erosion. Here, two ideas to reduce the erosion are proposed and experimentally confirmed using a small railgun which has 5 mm square bore. One is the method of a plasma initiation separated from the projectile (PISP method), the otheris the augmentation of the magnetic field by using a permanent magnet. The erosion of bore surface was reduced dramatically by applying those two ideas, and the performance of the railgun was improved.