It solves my problem and the plasma looks something like this. Almost evenly distributed across the cylinder.
But, sometimes due to foreign objects like metal pieces or mosquitoes inside the cylinder the entire discharge happens through a single spark (which is obvious). But that's not what I want; I want an even distribution of the plasma. I want to detect these sparks and shutdown the flyback for say 1 sec and then start it again(like in a hiccup mode) or report a fault with an LED.
I tried measuring the current via the R10 shunt resistor to find a change in current waveform during normal operation and during a spark, but I couldn't see much difference between the both. Is there a way to find the high voltage sparks and shutdown the circuit?
PS: I have limited knowledge of electrical engineering.