JPH043896A - Method and device for forming plasma armature of rail gun type electromagnetic accelerator - Google Patents

Abstract

PURPOSE:To form a plasma armature easily with good reproducibility by a method wherein line explosion plasma is blown into an accelerating hole through a fine hole and arc discharge is generated to form the plasma armature by a plasma forming material at a specified place. CONSTITUTION:A total current is conducted at first through a line explosion circuit simultaneously with the starting of electric discharge while plasma, generated by line explosion, is blown into an accelerating hole 2 through a fine hole 11. This phenomenon can be confirmed from the initial small peak of a signal from an optical probe provided near the small hole. When the value of current has arrived at about 20 KA after about 10 mus, new arc discharge is generated at a place whereat the fine hole 11 between rail electrodes 1, 1 is located and the current of the line explosion circuit is attenuated suddenly simultaneously with the generation of the arc discharge whereby the total current is shifted to an arc discharge current quickly. An arc discharge plasma 13 becomes a plasma armature moving with a speed of about 2.5-3.0 Km/s which can be understood from the optical probe signals of respective positions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rail gun type electromagnetic accelerator.

[Conventional technology]

A railgun-type electromagnetic accelerator (hereinafter referred to as a railgun) uses electromagnetic force to accelerate macroscopic objects at high speeds, which is difficult to achieve with methods that use the combustion gas of gunpowder or the expansion force of high-pressure gas. It has been attracting attention in recent years as it is possible to obtain projectile speeds higher than the above.

Two types of materials are used for the armature of a railgun: solid metal and plasma, but the method using a plasma armature is particularly useful when accelerating a small flying object weighing a few grams to ultra-high speed. It is mainly used as an accelerator to generate shock ultra-high pressure of more than 10 million atmospheres through the collision of materials, as a simulation device for the problem of rock collisions in outer space, and as a solid material for nuclear fusion reactors. It is expected to be used in hydrogen fuel pellet implantation equipment, etc., and development toward practical use is actively underway.

Regarding research and development of railguns and their utilization technology, please refer to IE
EE Transactions on Magnet
ics, vol, Mag20, No. 2 (1984)
, vol. Wag-22, No. (1986) and vol. 25. No. 1 (1989).

The acceleration principle and structure of a railgun using a plasma armature are shown in Figure 3fa) and (bl).An insulating flying object 3 is installed in an acceleration hole 2 between two rail-shaped electrodes 1, and a A metal plate or metal foil for forming a plasma armature 4
is installed to make electrical contact between the two rail electrodes. In this state, the ghost B of the capacitor bank etc.
When 5 is connected to two rails, switch 6 is closed, and power supply voltage is applied, the metal plate or metal foil becomes plasma due to the large current as shown in Figure 3 (bl). While maintaining a current of , continues to accelerate the projectile with a force proportional to the square of the current.

When accelerating a projectile using a rail gun, significant damage occurs to the surface of the rail electrode when the speed of the projectile is slow at the beginning of acceleration. This is because the moving speed of the plasma armature is slow in the early stages of acceleration, and a large current is concentrated in a narrow region on the surface of the rail electrode. Damage to the surface of the rail electrode not only mechanically deforms the cross-sectional shape of the acceleration hole, but also increases the mass of the plasma armature and reduces acceleration efficiency.

Therefore, N if! It has become common practice to reduce damage to the rail surface by initially accelerating the accelerating projectile using another method and increasing the moving speed of the plasma armature as much as possible at the initial stage of electromagnetic acceleration. In this case, it is necessary to form a plasma armature behind the projectile that is initially accelerated and enters the rail gun.The methods for this are: The forming material is glued together, and when the metal foil enters the rail gun together with the flying object and shorts between the rail electrodes,
A method of turning metal foil into plasma by applying a main voltage between rail electrodes (e.g. S, USUB^KJONDO, S,
5AWAOKA, IEEE Transacti
ons on Magnetics, vol, M
ag-20+ No, 2+ p260 (1984)) and (2) an additional pair of point electrodes are exposed on the insulator surface in the rail gun acceleration hole, and after the projectile passes through that position, a high voltage power source is applied. A method in which a spark is created between the point electrodes, and at the same time, the main power voltage is applied between the rail electrodes, inducing dielectric breakdown between the rail electrodes at that location and starting arc discharge (e.g. R,S,HAWKE,e
t,al,IEEE Transactions on
Magnetics, vol, 25. p219 (198
9))).

Although the above (11) is a simple method, gold vI4F
5, the short circuit between the rail electrodes is not reliable, and if the voltage of the main power source is applied between the rail electrodes while the short circuit is insufficient, there is a possibility that abnormal discharge will occur in other parts of the rail gun. As a countermeasure, a method has been reported in which a short circuit between rail electrodes caused by metal foil is detected, the metal foil is turned into plasma using a small power supply, and then the voltage of the main ft source is applied (Il, S, HAWKEet, al, IEEE Tr.
analyzes on Magnetics, v.
ol, Mag22, No. 6. p1510 (1989)
), which does not ensure short circuits through metal foils and has the disadvantage of requiring complex short circuit detection circuits and additional power supply circuits.

Method (2) does not require the attachment of metal foil or the like to the back surface of the projectile, so when, for example, multiple independent railguns are connected and electromagnetic acceleration is performed in multiple stages, the generation of plasma electrons in each railgun is possible. It can also be used as a method. However, as in the case of +11, an additional power supply circuit is required, and the delay time between generating the spark and applying the main Ti1l voltage across the rail electrodes must be precisely controlled. Furthermore, the presence of additional electrodes in the acceleration hole reduces the withstand voltage between the rail electrodes at that location, which can cause restriking plasma to occur during electromagnetic acceleration. The generation of this restriking plasma is considered to be the cause of the rapid decrease in the efficiency of electromagnetic acceleration.

[Problem to be solved by the invention]

The present invention solves the above-mentioned problems of the conventional technology in forming a plasma armature for a rail gun, and provides a method for reliably forming a plasma armature behind a flying object using a simple circuit, and a method for forming a rail gun type using this method. The aim is to provide a tM1 accelerator.

[Means to solve the problem]

In order to solve the above-mentioned problems, the inventors conducted extensive research and as a result, they came up with the present invention.

That is, the configuration of the present invention includes a railgun, a large current ti<switching system for supplying an accelerating current,
In the circuit consisting of a crowbar circuit), a new wire explosion circuit is connected in parallel with the rail gun, and its wire explosion section is installed in the cavity inside one of the rail electrodes, and 1isi
At the same time as the t pressure is applied, the line explosion plasma generated in the cavity is blown into the acceleration hole through the pores on the surface of the rail electrode, causing an arc discharge at a specific location between the rail electrodes. Forming a plasma armature at a specific location within the acceleration hole where no plasma-forming material, such as gold-X foil, is pre-existing, without installing additional electrodes and without using additional power supplies and switching systems. The problem was solved by the use of the rail gun's plasma armature-shaped line detonation circuit, which made it possible to
Figure (81) is a typical example of the present invention. The wire explosion part of the wire explosion circuit is a thin metal wire 8 installed in a cavity 9 inside one of the rail electrodes, and one end of this thin wire is in contact with the inner surface of the cavity. death,
The other end is connected to the other rail via a resistor 10. The cavity is connected to the acceleration hole via the pore 11. When the main power switch 6 is closed and voltage is applied to the rail gun and wire explosion circuit as shown in Figure 1 (bl), the main itt
The current ■ from the source first flows to the wire explosion circuit 8.10, and the thin wire 8 becomes plasma due to the wire explosion.
2 is blown into the acceleration hole through the pore at high speed, and at the same time the voltage across the wire detonation circuit is applied between the rail electrodes.

When the tip of the injected plasma reaches the rail electrode surface on the opposite side inside the acceleration hole, the insulation between the rails titFfA is broken, and the current from main 7: This arc discharge plasma 13 is accelerated by the magnetic force of 1 and comes to play the role of a plasma armature. 411! The delay time from the start of energization to the detonation circuit to the occurrence of arc discharge between the rail electrodes is an important characteristic for the present invention, and it depends greatly on the diameter of the thin wire in the wire detonation part, the volume of the cavity, and the diameter of the pores. Dependent. This delay time is required to be less than OI3, and therefore the thin wire of the wire explosion circuit is preferably a thin metal wire with a diameter of about 0.1 m, the volume of the cavity is several n', and the diameter of the pore is preferably 1 to 21. The voltage generated across the wire explosion circuit is determined not only by the above delay time but also by the arc T! Important for the transition speed to the first stream, 500 V or more 3k
V or less is required. Therefore, it is desirable that the resistance of the wire explosion circuit be several hundred mΩ.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

In the method shown in FIG. 1 (δ), a plasma armature formation experiment was conducted using a rail gun with a total length of 300 fi and a 1500 μF capacitor bank charged to 6 kV. A thin copper wire with a diameter of 0.1 m was used as the wire explosion part, and a resistance of 200 mΩ was used as the resistor. The diameter of the pore is 1.5fl,
The volume of the cavity including the pores is approximately 5.3 mm. The distance between both rail electrodes is 14 squares. The discharge current of the capacitor and the vA detonation circuit current were measured independently, and the formation and acceleration of the plasma armature inside the rail gun was measured using an optical probe installed along the acceleration hole to measure the light emission from the plasma. Evaluation was made by observation.

As a result, the results shown in FIG. 2 were obtained.

When the discharge starts, the entire current 14 first flows into the wire explosion circuit,
[The plasma generated by one shot is blown into the acceleration hole through the pore. This phenomenon can be confirmed from the initial small peak of the signal 16 from the optical probe placed near the pore. After about 10 as, when the current reaches about 20 kA, a new arc discharge occurs at the location of the pore between the rail electrodes, and with it the current in the line detonation circuit rapidly decays, and the total current is reduced to arc Rapidly transitions discharge to current. As can be seen from the optical probe signals 16.17.18 and 19.20, the arc discharge plasma is about 2.5~3.0
It can be seen that it is a plasma armature moving at a speed of km/s.

〔Effect of the invention〕

As described above, the method of the present invention using a wire detonation circuit connected in parallel with the railgun allows the addition of additional electrodes and additional [fi and switch systems] into the railgun acceleration hole where no plasma-forming material is present. Plasma armatures can be formed easily and with extremely good reproducibility without the use of a plasma armature. Further, the present invention provides a method for forming a plasma 1ifIi of one railgun each, and a railgun type iitM! It can also be effectively used as an L accelerator.

[Brief explanation of the drawing]

Figures 1 (a), (bl, and c) are schematic diagrams for taking detailed explanations of the present invention, Figure 2 is a sales diagram showing the results of examples, and Figure 3 (al , (bl is a schematic diagram for explaining the conventional technology. l: rail electrode, 2: acceleration hole, 3: flying object, 4: plasma forming material, 5: main 1tS, 6: switch, 7: plasma Armature, 8: Fine metal wire at the line field source, 9: Cavity, 10:
Resistor, 11: Pore, 12: Line explosion plasma, 13: Arc discharge plasma (plasma electron), 14: Total current, 15: Line explosion circuit i current, 16 to 20: Signals from each optical probe. Agent frJx person Yamaguchi JL i'-,', shi\'-;゛, 1 no 1. ”-1-No. 1.7 T1-Summary II+!-bs)

Claims (1)

[Claims] 1) In a circuit consisting of a railgun type electromagnetic accelerator and a large current power supply (including a switching system and a crowbar circuit) for supplying acceleration current, a line explosion circuit is newly added to the railgun type electromagnetic accelerator. The line explosion part is installed in the cavity inside one of the rail electrodes, and when the power supply voltage is applied, the line explosion plasma generated in the cavity passes through the pores on the surface of the rail electrode and accelerates into the hole. It is characterized by forming a plasma armature at a specific location within the acceleration hole where no plasma-forming material such as metal foil already exists by blowing into the inside and causing an arc discharge at a specific location between the rail electrodes. A method for forming a plasma armature for a railgun type electromagnetic accelerator. 2) In a rail gun type electromagnetic accelerator having a large current power source that supplies an accelerating current, this electromagnetic accelerator is connected in parallel with the rail gun type electromagnetic accelerator, and is provided in a cavity inside one of the rail electrodes and has a power source. A rail gun type electromagnetic accelerator characterized by comprising a line explosion circuit consisting of a line explosion section that forms a plasma armature within an acceleration hole by applying voltage.