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

Abstract

Acceleration of high energy ions was observed in z-pinches and dense plasma foci as early as the 1950s. Even though many theories have been suggested, the ion acceleration mechanism remains a source of controversy. Recently, the experiments on the GIT-12 generator demonstrated acceleration of ions up to 30 MeV from a deuterium gas-puff z-pinch. High deuteron energies enable us to obtain unique information about spatial, spectral and temporal properties of accelerated ions. In particular, the offaxis ion emission from concentric circles of a ∼1 cm diameter and the radial lines in an ion beam profile are germane for the discussion of acceleration mechanisms. The acceleration of 30 MeV deuterons can be explained by the fast increase of an impedance with a sub-nanosecond e-folding time. The high (>10 Ω) impedance is attributed to a space-charge limited flow after the effective ejection of plasmas from m=0 constrictions. Detailed knowledge of the ion acceleration mechanism is used with a neutron-producing catcher to increase neutron yields above 10 13 at a currentof2.7 MA.

Characteristics of fast deuteron sources generated in a dense plasma focus

“…It should be noted that the ion image recorded by the axial pinhole camera (see Fig. 7d) was composed of some concentric azimuthal arcades with the center in the z-axis, similar as in many other PF and Z-pinch experiments, e.g., described in papers [4,13,20,22]. The ring-shape spots are more intense within the same circular slice at the angle of about 120°.…”

“…The considered sources formed a concentric and/or radial complex image composed of numerous spots of dimensions ranging up to 0.5 mm. A similar circular and radial distribution of the sources emitting MeV-deuterons was also observed in a mega-ampere gas-puffed z-pinch experiment [13]. The acceleration of the deuterons to energy > 20 MeV was explained by a plasma diode mechanism at an increase in the zpinch impedance (> 10 ) during a sub-nanosecond time.…”

“…The model of the magnetic reconnection has also been applied for denser plasmas produced by the interaction of focused laser beams with some targets [2,3], when the internal current jets and magnetic fields can evolve and become self-organized. In Z-pinch and dense plasma-focus (PF) experiments, the problem of the fast particle acceleration has been studied and discussed for a long time, in many papers [4][5][6][7][8][9][10][11][12][13]. At the deuterium gas filling the accelerated fast deuterons can produce fusion neutrons by a beam-target mechanism.…”

Evolution of a Pinch Column During the Acceleration of Fast Electrons and Deuterons in a Plasma-Focus Discharge

“…It should be noted that in the recorded interferometric fringes, there was no experimental information about the acceleration of fast charged particles in the interrupted pinch region (filled up with low-density plasma). Such a possibility in Z -pinch discharge was discussed (see [8]).…”

“…In discharges with the deuterium filling, the hard X-rays (HXRs) and fast neutrons (produced by D-D fusion reactions) supply an indirect information about fast electrons and deuterons, and particularly about instants of their production, directions of their motion, and energies. The characteristics of the Z -pinch and plasma-focus discharges and different models of the fast particle acceleration were described in detail in [1]- [8]. In research on space and fusion plasmas, the magnetic reconnection was often indicated as a source of the fast electron and ion beam acceleration [9]- [12].…”