T. Sueda

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.

Streamer discharges by pulsed power on a spiral transmission line

Streamer corona discharges produced by pulsed power make enough high energy electrons to dissociate gases directly. Consequently, pulsed streamer discharges have been proposed for the removal of NO/sub x/ and SO/sub 2/ from flue gases, the production of ozone and the treatment of poisonous gases. It is proposed here to produce the pulsed streamer discharges on a spiral transmission line. The characteristics of the discharges are studied, comparing with results using a PSpice code. Then, the effectiveness and advantages of the spiral transmission line are discussed in view of real applications.

Interferometer Measurements in Pulsed Plasma Experiments

The interferometer measurements are extremely informative in plasma experiments allowing direct evaluations of the electron density. The primary goal of the work presented, is to build a laser interferometer which meets the requirements of the highest possible simplicity, economy, convenience and ease of construction. These requirements are successfully satisfied while maintaining high sensitivity (±0.5°–of phase shift) and a wide density range (1014 and 1019 cm-2–line-integrated) of the interferometer. In our experiments we used a low average power (5 mW) He–Ne laser without complicated and costly stabilization or detection environments. The He–Ne laser interferometer with the Michelson arrangement was used to measure the line-integrated plasma densities in various plasma experiments. Time- and spatially-resolved density measurements were performed for a plasma opening switch, a laser produced plasma, an electrothermal launcher and railgun plasmas.

Early phenomena of capillary discharges for an electrothermal gun

The 80 kJ electrothermal gun facility at Kumamoto University was assembled in order to investigate the phenomena of capillary discharges and to determine parameters of plasmas produced by a high power pulse discharge in the capillary. The behavior of capillary discharges is observed by using an image converter camera in order to make clear the early phenomena of the capillary discharge in different ambient pressures. The behavior of early capillary discharges varies from arc discharge to surface discharges with decreasing ambient pressure.

Behavior of Capillary Plasmas with Different Diameters

During the early phase of electrothermal gun operation, the operation characteristics improve at low ambient pressures because the discharge occurs on the surface of the capillary, resulting in a higher rate of wall ablation and a higher capillary plasma density than in the case of operation at higher ambient pressures. In addition, it has been reported that reduction of the capillary diameter at low pressures results in an increase in the kinetic energy of the projectile. At low pressures, an electrothermal gun with a small capillary diameter is therefore superior to one with a large capillary diameter. In order to understand these experimental results clearly, we measured the plasma parameters of electron density and temperature, which are strongly related to the operation characteristics of the electrothermal gun, for different capillary diameters using a spectroscopic technique, and compared the results with results for a zero-dimensional time-dependent model. The electron density of the capillary plasma increases with decreasing capillary diameter.

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.

Pulsed power generators using an inductive energy storage system

The pulsed power generators using an inductive energy storage system are extremely compact and lightweight in comparison with those using a capacitive energy storage system. The reliable and repetitively operated opening switch is necessary to realize the inductive pulsed power generator. Here, the pulsed power generators using the inductive energy storage system, which have been developed in Kumamoto University, are summarized.

Dependence of railgun operation on current rise time

Railguns are facilities to accelerate projectiles up to several kilometers per second by electromagnetic force generated by driving current. Worldwide, a variety of current waveforms are used in railgun systems. This paper describes the dependence of railgun operation on the rise rate of the driving current. The use of the exploding wire as an opening switch makes it possible to change the rise time of the driving current. A secondary arc is likely to appear and the erosion on a rail surface is more severe when current with a short rise time is used. According to the nondimensional railgun simulation, current with a short rise time heats up the plasma so fast that many particles ablated from the bore surface, which seem to be the cause of the secondary arc, increase rapidly in the early phase of acceleration.

Characterization of capillary plasmas with different diameter [electrothermal guns]

The operation of an electrothermal gun is strongly related to capillary discharges. The operation of an electrothermal gun with a small capillary diameter is superior to one with a large diameter in the vacuum. In order to understand these experimental results clearly, the plasma parameters of electron density and temperature, which are strongly related to the operation characteristics of the electrothermal gun, were measured for different capillary diameters by spectroscopic and interferometer measurements. The electron density and temperature of the capillary plasma increase with decreasing the capillary diameter. The early operation of the electrothermal gun with a small capillary diameter is superior to that with a large capillary diameter because of the increase of the capillary plasma pressure. The electron density was also measured by an interferometer measurement in order to validate the density estimated by the spectroscopic measurement. The electron densities, 10/sup 17/-10/sup 19/ cm/sup -3/, estimated by the interferometer measurement agree with those from the spectroscopic measurement.

Modification of railgun plasma characteristics by spout holes on the bore

In a plasma armature railgun, spout holes made on the bore to exhaust some part of the plasma is one possible way to suppress the plasma armature broadening due to wall ablation. This paper describes how the railgun plasma is modified by the spout holes. Mach-Zehnder interferometry using a He-Ne laser enables the electron density distribution to be obtained over the plasma armature by a single shot. Electron density distribution in two cases of railguns without and with spout holes were compared. The distribution in case of the railgun without spout holes was mostly obtained and the value was 1.3/spl times/10/sup 19/ cm/sup 3/ at most. In the case of a railgun with spout holes, on the other hand, the distribution was partly missed since the laser beam was deflected due to high density gradient in the plasma. However, the obtained fractional distribution was good enough to see a difference from the other. The high density region was much narrower than that in the case without spout holes, namely, the spout holes made the plasma compact.