This is a simple solid state Tesla coil with one MOSFET
Step 1: What You Will Need
IRF 540 MOSFET (other similar mosfets will work IRF 510, 630)
50 Ω resistor
1 kΩ pot
1 μF capacitor
Cardboard, glass or bakelite tube
Step 2: Operation
The secondary coil gest warm or hot, use cardboard, bakelite or glass tube. The secondary is made of magnet wire 200 - 400 turns, 0.1 - 0.2mm thickness. The coil dimensions are not critical (30 - 40 mm diameter)
The primary is only 1 turn, 4-5mm bigger in diameter than secondary, 1mm magnet wire, placed at the bottom of the secondary.
Turn the 1k pot when the spark discharge appears on the top of the secondary. At best adjustment the spark is longest and the mosfet gets warm slowly. If it don't oscillate, change the connections of the primary!
Resonant frequency depends on secondary coil dimensions and number of turns. It's between 2 and 10 MHz.
If you operate this tesla coil at higher performance (40-50W) the mosfet gets hot, it requires large heatsink.
Placing a top capacitance to the secondary, the spark gets longer, and the mosfet will be cooler.
The spark produces ozone!