Generating plasma flame with neon transformator
10 kV AC is not going to jump very far, maybe 0.3 cm.  You will need to initiate a spark by briefly touching the leads together, then drawing them apart. Or you could build a Jacob's ladder to cause the plasma arc to travel up the rails until the gap is too wide to support the arc.

Never handle the wires directly to avoid such unpleasantries as death by electrocution.