Coulomb explosion of “hot spot”

Abstract

The study presented in this paper has shown that the generation of hard x rays and highenergy ions, which are detected in pinch implosion experiments, may be associated with the Coulomb explosion of the hot spot that is formed due to the outflow of the material from the pinch cross point. During the process of material outflow, the temperature of the hot spot plasma increases, and conditions arise for the plasma electrons to become continuously accelerated. The runaway of electrons from the hot spot region results in the buildup of positive space charge in this region followed by a Coulomb explosion. The conditions for the hot spot plasma electrons to become continuously accelerated have been revealed and estimates have been obtained for the kinetic energy of the ions generated by the Coulomb explosion.A Z pinch is an electrical discharge in plasma, which is compressed under the action of the magnetic pressure produced by the intrinsic discharge current [1][2][3][4][5][6][7]. Typical of Z pinches is the formation of hot spots due to the development of large-scale MHD instabilities [1,2,8-10].The discharge plasma column is deformed during compression, which is accompanied by the formation of necks smaller in radius than the main column. The magnetic pressure in the neck region increases, resulting, first, in faster compression and, second, in material outflow from the neck region in the axial direction. The final stage of the necking is a hot spot.Apparently, the axial jets were first detected in an experimental study [11] where the process of compression of deuterium pinches was investigated. As these jets were accounted for by an increase in neutron yield, the authors of Ref.[11] proposed a "noncylindrical Z pinch" in which the formation of the hot spot was predetermined by the geometry of the discharge.Subsequently, this configuration was called a plasma focus [12,13]. In subsequent experiments on a deuterium plasma focus at currents of about 1 MA, electron beams, hard x rays, and "epithermal" deuterons with energies up to 8 MeV were detected [14]. Even more energetic deuterons with energies of several tens of megaelectron-volts were detected in experiments with deuterium liners imploded at a current of 2.7 MA [15]. To explain the generation of high-energy ions and hard x rays, the so-called "target" mechanism was proposed [16]. It is assumed that in the final stage of formation of the hot spot, displacement currents occur that generate strong electric fields in which charged particles are accelerated.

Ion acceleration mechanism in mega-ampere gas-puff z-pinches

“…In our case, however, the ion acceleration by elastic collisions in a compressed z-pinch [8,[29][30][31] cannot explain 30 MeV deuteron energies, ion emission originating outside a neck, and high ion emission anisotropy observed in our experiment (small anisotropy of ion emission could arise even from initially isotropic distribution because of the influence of azimuthal magnetic fields on ion trajectories [32]). The latter two observations also rule out the gas-dynamic model of a neck [8,33] and the Coulomb explosion of hot spots [34]. Another hypothesis is the formation of energetic ion tail by microturbulences [7,[35][36][37].…”

Wire Explosion in Vacuum

“…(II-10) Thus, under the assumptions made [see (21)], the integrated growth rate of ETIs in an exploding material does not depend of the explosion regime and is determined only by the constants of the material. Steiner et al [160] investigated experimentally how the growth of ETI depends on the criticalto-melting temperature ratio and argued the validity of relation (23). It should be noted that expression (20) assumes a constant specific current action integral; however, this assumption is not always valid.…”

Hybrid MHD/PIC simulation of a deuterium gas puff z pinch

“…neutron production due to high ion temperature), ion acceleration due to the axial plasma outflow from a constriction, generation of fast ion in the low dense plasma surrounding the pinch column, target mechanism [15], coulomb explosion [16]. The last two mechanisms are not considered in our model because of assumption of plasma quasineutrality.…”