Relation between filamentary current sheath and ionization energy in a plasma focus
Summary form only given. Since the discharge current I grows in a sinusoidal form in a plasma focus, one can predict the formation of a filamentary current sheath (CS) in the breakdown and early rundown phases when I is small and the specific plasma energy /spl epsi/<1 MJ/g, the energy required to ionize the whole swept gas. This has been verified by the experimental results obtained on a small Mather-type plasma focus device (20 kV, 18 kJ) with use of a laser differential interferometer, I=23-270 kA (I/sub max/=350 kA), p/sub D2/=2.5 torr for neutron emission. The uniform initial CS formed along the insulator surface soon develops into filaments during moving towards the outer electrode driven by the Lorentz force. It then develops into muddled filaments after crossing the coaxial electrodes. Later the filaments re-join to form a uniform CS (I>200 kA) which accelerates towards the open end of the coaxial gun and forms the pinch there.