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

Abstract

Plasma in a pinch column, as produced by a plasma-focus discharge at the deuterium filling and the current intensity reaching 1 MA, was investigated at the total neutron yield reaching about 10 10 per discharge. The use was made of neutron diagnostics, laser interferometry, soft X-ray measurements, optical emission spectroscopy, magnetic probes, as well as electron and ion measurements with the temporal, spatial, and energetic resolutions. The detailed studies showed the ordered toroidal, helical, and plasmoidal structures which could contain currents with poloidal and toroidal components and their associated magnetic fields. Their spontaneous transformations were explained by changes in a topology of magnetic field lines due to magnetic reconnections. A nonthermal acceleration of fast electrons and ions (producing hard X-rays and fusion neutrons, respectively) corresponded to: 1) the formation of plasmoids in the pinch column and 2) a decay of pinch constrictions and secondary plasmoids during the evolution of instabilities. A filamentary structure of the current flow could explain the high energy density and fast transformations of the magnetic energy into kinetic energy of electron and ion beams (reaching energy of hundreds of kiloelectronvolt). This paper summarizes the results obtained with the PF-1000 facility in 2009-2017, and describes the internal transformations in a dense plasma column during the evolution of MHD instabilities.

Update on the Scientific Status of the Plasma Focus

“…The evolution of a pinch column during the acceleration of deuterons (and electrons) in PF discharges was also subject of another study [103]. Using different diagnostic techniques in the PF-1000 facility, it was demonstrated that inside the pinch column there were formed different ordered plasma structures which contained local currents with poloidal and toroidal components and associated magnetic fields.…”

“…The interferometric system described in Section 3.2.1 enabled visualization of internal structure of the plasma from radial implosion phase until plasma decay in a sequence of 15 frames recorded in a single shot. Results of such investigations are described in a series of publications [103,[105][106][107]126,[391][392][393][394][395][396][397], including an overview paper [103]. Measurements of neutron, soft X-ray (SXR) and hard X-ray (HXR) emissions provided context for the interferometric observations.…”

“…(5) The early part of first phase of neutron emission was shown to coincide [103] with axial movement of the plasmoid formed near the bottom of the plasma column (see Figure 92). (5) The early part of first phase of neutron emission was shown to coincide [103] with axial movement of the plasmoid formed near the bottom of the plasma column (see Figure 92). [397] (Phys.…”

Properties of toroidal magnetic fields in axial plasma flow on the PF-1000U plasma focus facility

“…The formation of such plasmoids was shown earlier in papers (Kubes et al. 2012, 2019) using laser interferometry and magnetic probes. In figure 1( a ) we also show a schematic of the sequential positions of the PCS at different points in time, the formation of a pinch at the end of the anode and the region of propagation of the plasma flow along the axis of the facility.…”

“…The development of instabilities m = 0 causes an interruption of current, reconnection of magnetic field lines and the formation of a plasmoid with a captured magnetic flux (Krauz et al 2020). The formation of such plasmoids was shown earlier in papers (Kubes et al 2012(Kubes et al , 2019 using laser interferometry and magnetic probes. In figure 1(a) we also show a schematic of the sequential positions of the PCS at different points in time, the formation of a pinch at the end of the anode and the region of propagation of the plasma flow along the axis of the facility.…”