Evolution of the small ball-like structures in the plasma focus discharge

The ball-like structures were observed on the PF-1000 device at the shots with the deuterium or neon fi lling and deuterium puffi ng usually outside of the dense-pinched plasma column. The short description of the ball-like structures observed in shot #10080 and #10122 was presented in a paper [1]. In that paper, it was observed that the ball-like structures occurred at the imploding plasma shell boundary, the lifetime of the structures could be longer than 200 ns, the maximum electron density in the center of such structures was about 1025 m–3. The ball-like structures had an internal region without clear interferometric fringes at the very beginning of their existence. During the existence of the ball-like structures, their internal regions were fi lled by interferometric fringes step by step, before they started to decay. The author suggested that the internal region without clear pattern of fringes was caused by internal turbulent behavior with velocities determined by the duration of the diagnostic laser beam above 106 m/s. Structures decayed by absorption in the expanding column with the decreasing of the electron density or by ejection of a plasma jet [1]. In this paper, the more detailed characteristics formulated from 15 shots (i.e., electron density profi les and total electron number of the ball-like strucEvolution of the small ball-like structures in the plasma focus discharge Balzhima Cikhardtova, Pavel Kubes, Jakub Cikhardt, Marian Paduch, Ewa Zielinska, Josef Kravarik, Karel Rezac, Jiri Kortanek