Characterisation of electric discharge in hollow electrode Z-pinch device by means of Rogowski coils

Abstract

The hollow electrode Z-pinch (HEZP) is expressed as a new shape of Z-pinch devices in which one of the electrodes is ring-shaped. The periodic time of the discharge current is $35\ \mu \hbox {s}$ with a total system inductance of 288 nH, total system resistance of $14\ \hbox {m}\Omega$, and 34% deposited energy for a charging voltage of 8 kV. The pinch effect appears in the shape of a sharp spike in the signal of the discharge voltage and dip in the signal of discharge current, which leads to an increase in the plasma inductance at the pinch time. The plasma current density, which is measured using miniature Rogowski coil for 8 kV charging voltage and 1 torr pressure, has a maximum value of $12.1\ \hbox {kA}/\hbox {cm}^{2}$ near the axis of the discharge tube and decreases toward the wall. The helium gas pressure in the range of 1–2 torr expresses the situation of the maximum current density. The pinch time increases by increasing the gas pressure and also by decreasing the charging voltage leading to a decrement of the peak discharge current and hence the magnetic field is also decreased. A delay time of at least $4.1\ \mu \hbox {s}$ is found to be required to form the pinch for the implemented set-up of anode–cathode dimensions and interdistance. The calculated sheath velocity is in the range of 1.2–$6\ \hbox {cm}/\mu \hbox {s}$ which is directly proportional to the charging voltage and inversely proportional to the gas pressure.