Complex sentence: When the potential across the capacitor reaches around 10kV the spark gap breaks down and the capacitor discharges violently through the inductor followed by a rapid ring down of the LC circuit formed between the capacitor and primary coil through the ionized spark gap.
Split into simpler sentences: When the potential across the capacitor reaches around 10kV, the spark gap breaks down and the capacitor discharges violently through the inductor. Then followed by a rapid ring down the LC circuit formed between the capacitor and primary coil through the ionized spark gap.