Microwave radiation in the electrical explosion of conductors

Moscow. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 1, pp. 3–5, January–February, 1995     

Self-similar electrical skin explosion of a conductor

We examine the problem of the electrical explosion of a conductor with flat boundary in a strong magnetic field. We estimate the role of heat conduction in order to determine the critical electrical fields in which fusion and vaporization of the metal take place. The characteristic features of the explosion of a layered medium are examined.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 10, No. 3, pp. 21–26, May–June, 1969.The author wishes to thank L. M. Barkov for discussions of the questions examined above.     

电爆炸过程中金属丝阻抗的变化

为了掌握金属丝阻抗的变化规律,通过分压器和罗氏线圈分别测量出电爆炸过程中金属丝上的电压和电流,并由此计算出金属丝阻抗等相关电参数随时间变化的规律;采用F.D.Bennett和A.Hobson模型对金属丝阻抗进行了数值模拟,得到金属丝阻抗随时间的变化规律。实验结果和模拟结果的比较表明:两个模型的模拟结果均在金属丝气化前和部分初始放电电压下有效;当放电时电容器初始电压较大时,能量沉积速度更快,金属丝液化、气化、完全气化所用的时间更短;在金属丝爆炸过程中,金属丝阻抗存在一个最大值。     

The nature of the electrical impulse in an explosion

The mechanism for the formation of an electric impulse on the explosion of ordinary explosive substances is analyzed. A double electrical layer with voltage of the order kT 0.2–0.6 V is formed in the detonation wave. When the detonation wave passes to the outer surface of the charge, electrons adhere to molecules of air and explosion products. As the charged explosion products fly apart, the distance between the positive and negative charge s increases and the voltage increases to a magnitude of the order of a kilovolt. The asymmetric separation of the charged explosion products is the cause of the impulse. Theoretical estimates are compared with experiments [1].Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 11, No. 2, pp. 72–75, March–April, 1970.The authors are grateful to Ya. B. Zel'dovich and Yu. P. Raizer for useful discussions.     

侵彻爆炸条件下岩石边坡破坏效应的数值模拟

运用爆炸冲击非线性有限元理论,对侵彻爆炸条件下岩石边坡的破坏,如爆炸成坑效应、爆炸波传播过程进行了模拟,算例结果验证了本文方法的有效性。在此基础上,假定在拉力作用下单元可以分离,岩石单元和炸药单元之间都为可破坏接触面,对岩石破碎过程进行了模拟,算例结果与实际情况比较符合。     

Oscillographic study of electrical explosion in copper and gold

An oscilloscope is used to measure electrical resistance as a function of enthalpy in copper and gold during the process of electrical explosion of wire samples. The enthalpy at the initial point of the explosion process was greater in value than at the melting point of the metal. The electrical explosion phenomenon is considered from the viewpoint of the kinetics of the liquid-metalvapor transition under impulse-heating conditions. The degeneration of the initial point of the electrical explosion for liquid-phase heating over periods less than 10^–7 sec is explained by disruption of the stability of homogeneous-vapor-nucleus formation.Translated from Zhurnal Prikladnoi Mekhaniki Tekhnicheskoi Fiziki, No. 3, pp. 54–58, May–June, 1974.     

铜丝电爆炸的光谱分析

通过搭建脉冲成形网络放电模块和光谱测试系统,利用Andor SR750光谱仪测量了铜丝电爆炸等离子体在400~500nm范围内的发射光谱。根据热力学平衡理论,采用双谱线相对强度法计算了等离子体的激发温度,并研究了激发温度随时间变化的特性。研究结果表明,铜丝电爆炸产生的稳态等离子体的激发温度约为5 400K。在脉冲放电前期,激发温度变化较大;在放电后期,激发温度较稳定;整个脉冲时间内激发温度差约达800K。

     

Statistics of the fragments forming with the destruction of solids by explosion

The article sets forth one of the possible approaches to the construction of a size distribution function of the fragments. The Rozin-Rammler law for the distribution is obtained from general theoretical probability consideration. The theoretically obtained distribution function was verified in a large number of experiments. The experimental data are in good agreement with the theoretical deductions.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 87–100, March–April, 1971.     

水中金属丝电爆炸动力学过程的零维模型

金属丝电爆炸包含丰富的物理内容,近年来国内的实验和理论研究取得了重要进展,理解该过程有助于完善Z箍缩及磁加载等离子体动力学过程的物理建模,校验物性参数。在自相似运动假设条件下,发展了冷启动计算的水中电爆炸丝零维动力学模型。从一维磁流体模型出发,推导了描述丝等离子体膨胀的零维动能方程和内能方程,采用实际气体状态方程和修正的李-莫尔电导率参数作为封闭条件,根据质量守恒及水中激波雨贡纽关系式获得了丝等离子体的边界条件。应用于水中铜丝电爆炸动力学过程和能量转化分析,结果表明：该零维模型的物理假设合理,在一定范围内改变丝直径等参数可产生不同的放电模式,与一维模型及实验结果符合较好,能够为同类实验的优化设计和数据分析提供参考。     

Aluminum micro-particles combustion ignited by underwater electrical wire explosion

The results of experiments on the ignition of aluminum micro-particles’ combustion by underwater electrical wire explosion (UEWE) are reported. A compact sub-microsecond timescale duration high-current (240 kA) pulsed power generator was used to explode copper and aluminum wires electrically in different aluminum powder suspensions. The combustion of the aluminum micro-particles was characterized by a target time-of-flight method and optical measurements of the exploding wire and aluminum suspension light emission. It was shown that, by using a proper solution and type of aluminum powder, this method allows aluminum micro-particle combustion in the estimated range of 32–79 % efficiency.     

Formation of a spall cavity in a dielectric during electrical explosion

The wave dynamics of the stress-strain state of a solid dielectric during electrical explosion near its surface is analyzed. A quantitative model of an electrical explosion is developed which describes the operation of a high-voltage generator, the expansion of the discharge channel, and the generation and distribution of shock-wave perturbations. Two mechanisms of formation of a spall cavity on the surface of the solid are considered: the less energetic mechanism implemented by means of the waves reflected from the surface, and the more energetic mechanism in which result from the action of a direct wave of compressive stresses. The effects of the reflection surface shape and the mode of energy input into the channel on the possible fracture pattern are estimated.     

Expansion of the luminescence zone in the electrical explosion of thick wires

This paper gives the results of experimental studies of the expansion of the luminescence zone associated with the electrical explosion of copper wires 0.74 mm in diameter and 20 cm long. It is demonstrated that the time dependence of the diameter of the luminescence zone coincides with the law of motion of a self-similar cylindrical shock wave. The energy of hydrydynamic motion has been determined for different energies introduced into the metal. The fraction of vaporized wire is estimated.     

Comparative characteristics of strong shock and detonation waves in bubble media by an electrical wire explosion

Strong shock and detonation waves in inert and chemically active bubble media, which are generated by a wire explosion initiated by a capacitor with a stored energy $W_0 =12.3$ –1,600 J, is experimentally studied. The measurements are performed near the wire and far from the wire in a vertical shock tube 4.5 m long with a volume fraction of the gas in the medium $\beta _0 =1$ –4 %. It is shown that in inert bubble medium, a short intensely decaying shock wave (SW) with intense pressure oscillations is formed in the vicinity of wire explosion point; near the explosion point at $\beta _0 \le 2$  % the SW propagates with the velocity of sound in a liquid. In chemically active bubble medium, an unsteady detonation wave generated by a wire explosion is formed. The pressure amplitude and the velocity of this wave are greater and the length is smaller than those of SW in an inert bubble medium in the same range of explosion energy. It is found that in the interval of low energy explosion from ${\sim }12$ to 64 J, the formation of the bubble detonation wave occurs faster than that at high energies ( $3\times 10^{2}$ – $10^{3}$  J).     

高压泄爆导致的二次爆炸

基于计算结果和相关实验结果,通过理论分析,对高压泄爆导致的二次爆炸机理进行了系统的阐述。泄爆后,泄出的高压可燃气体在泄爆口附近形成可燃云团,由于欠膨胀,云团内存在稀疏波低压区和Mach干高压区。火焰射流泄出后,在一定条件下,可使Mach干高压区内的可燃云团爆炸式燃烧,压力迅速上升,以致产生二次爆炸。