After initial success I thought of better way, more automatic. 

So I've built structure (that holds Tesla coil and powerful fan) and shield that will hold and cool Tesla coil and won't let radiation escape

Basically, it's a 3D printed cone with aluminium shield on it (not in the picture, already removed it)

The problem started once I've grounded the aluminium shield. Something went wrong, before I know it device went kaput. 

Well, I've replaced burned IRF250 and tried again making sure everything is far enough from grounded shield. It work for a minute much less powerful than usual and burnt again. I've changed MOSFET again, each time it was worse than previous ... 

Arrr... 

I guess the grounded shield changed capacity of resonant circuit