A. Ali’s research while affiliated with International Islamic University, Islamabad and other places

In this research work, time resolved measurements of floating potential, electron temperature and number density were performed in air discharge plasma. A symmetric tungsten triple probe diagnostic and circuitry were developed to diagnose DC discharge at different operating conditions. Motivation behind the direct access of electrical probe diagnostic to the plasma chamber was stemmed from the need to characterize the plasma for time resolved measurements of the discharge parameters with high accuracy. The error analysis showed that overall inaccuracy in the measurements for electron temperature and number density remained in the range of 8.2–11.6% and 7.65–13.9%, respectively. Traditionally, the error in electrostatic probe measurements is typically 20% for electron temperature and 50% for electron number density. Although these values are sufficiently large, the given analysis on consecutive measurements under same operating conditions yielded the data with high accuracy. The time resolved spectra of floating potential, investigated at all applied voltages, showed negligible variations in potential wave shape over time. However, the pressure dependent spectra predicted that the floating potential changed into sinusoidal waves of growing amplitude at higher air pressures. Overall floating potential was appreciably decreased with rise in air pressure.

This study investigated the temporal profiles of electron temperature and number density in rectified DC air discharge generated with a 50 Hz step-up transformer. An in-house built triple Langmuir probe and circuitry were used to diagnose the plasma parameters as a function of input voltage and filling gas pressure. A tungsten metal wire capable of withstanding the high temperatures was used as probe tip material. The temporal profiles revealed an increase in electron temperature with input voltage in the range of 380 to 450 V, whereas, an inverse relation between number density and input voltage was evident in the given work. The observed trend in the plasma parameters was absolutely reversed in case of the filling gas pressure. The electron temperature linearly decreased with an increase in pressure from 1 to 4 mbar, whereas a linear increase in number density with pressure was seen in the temporal profiles. Finally, it was concluded that the results for the tested plasma parameters were consistent and the in-house built probe functioned well in DC discharge for the used range of voltage and filling pressure.