Ultra-High-Speed Photographs Refuting ``Cohesion in Plasma''

Abstract

In a recent issue of this journal [M. A. Cook and W. S. McEwan, J. Appl. Phys. 29, 1612 (1958)] and in a recent book [Melvin A. Cook, The Science of High Explosives (Rheinhold Publishing Corporation, New York, 1958), 1st ed., pp. 158, 420–426], a sequence of framing camera pictures was presented, and the sequence was interpreted as evidence that, as the result of the detonation of a quantity of explosive, a plasma was ejected into the atmosphere, and that the plasma exhibited a strong cohesive force. This paper presents pictures of an essentially identical subject, taken at three exposure times: the same exposure time used for the sequence in the references (4 μsec); 1/20th of that time; and 1/400th of that time. These pictures show that the phenomena are those of a shock wave, and that no new assumption of cohesive force is necessary to interpret the pictures. A simple analysis of the shock wave interpretation using the usual theory is presented to show that the interpretation is consistent with the known properties of air and the explosive used.

Measurement of time-varying electron density of the plasma generated from a small-size cylindrical RDX explosion by Rayleigh microwave scattering

“…One end of the bare explosive was connected to a detonator and the other end was attached to the circular hole. The explosively generated plasma ejected from the circular hole into the measurement region was the research object in this paper [3][4][5][6][7]. All explosives were fired by electric detonators that were initiated by a capacitive discharge unit (FD100, Yingkou Feiya Technology Co., Ltd, China).…”

“…A large number of charged particles are generated from a condensed explosive, which form a certain volume of weakly ionized non-ideal plasma [1,2]. This plasma is transient and time-varying and is called an explosively generated plasma [3][4][5][6]. This is an important object for studying the thermodynamic and electromagnetic effects from explosions.…”

“…Tasker et al explored the applications of explosively generated plasma in the field of engineering [14][15][16]. In this research, the plasma generated from the end face of a small explosive confined by a guide tube is usually taken as the research object [3][4][5][6][7]. The macroscopic size, spectral characteristics, and peak electron density of the explosively generated plasma have been studied using optical instruments [6,7] and a charge-probe [3].…”

Sensitivity of Explosives.

“…The rapid heat pulse, termed "flash-across," is qualitatively analogous to the hypervelocity wave AB in figure 5, but it has been reported to propagate much faster (up to 100 km./-sec.). An increase of electrical conductivity of the solid explosive behind the shock front ifi an observed fact (10), but its quantitative consequences (71), as well as the interpretation of the photographic evidence of high electronic density phenomena sup-porting the heat-pulse theory (39), are the matter of some controversy.…”

The interaction of explosively generated plasma with explosives

“…It is known that the temperature of the plasma is of the order of 1 eV depending on the test configuration [1][2][3][4][5]. It has been shown that gaseous ejecta or plasma from detonating high explosives travel at 10 km/s in cylindrical shock tubes [1,[6][7][8] and can be focused in conical shock tubes to achieve impact velocities as high as 25 km/s (this work, framing camera studies).…”