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We have investigated the evolution of a system of sparking discharges in theinner acceleration region (IAR) above the pulsar polar cap. The surface of thepolar cap is heated to temperatures around $10^6$ K and forms a partiallyscreened gap (PSG) due to thermionic emission of positively charged ions fromthe stellar surface. The sparks lag behind the co-rotation speed during theirlifetimes due to variable $E$x$B$ drift. In a PSG the sparking discharges arisein locations where the surface temperatures go below the critical level ($T_i$)for ions to freely flow from the surface. The sparking commences due to thelarge potential drop developing along the magnetic field lines in these lowertemperature regions and subsequently the back streaming particles heat thesurface to $T_i$. The temperature regulation requires the polar cap to betightly filled with sparks and a continuous presence of sparks is requiredaround its boundary since no heating is possible from the closed field lineregion. We have estimated the time evolution of the sparking system in the IARwhich shows a gradual shift in the spark formation along two distinctdirections resembling clockwise and anti-clockwise motion in two halves of thepolar cap. Due to the differential shift of the sparking pattern in the twohalves, a central spark develops representing the core emission. The temporalevolution of the sparking process was simulated for different orientations ofthe non-dipolar polar cap and reproduced the diverse observational featuresassociated with subpulse drifting.

Two Dimensional Configuration and Temporal Evolution of Sparking discharges in Pulsars