Direct Induction is the method used in conventional tokamaks: an electric field is applied by ramping down the current in th ecentral solenoid, and breakdown and current cascade begins ina poloidal field null.

Merging Compression, pioneered on START at Culham, forms plasma rings at large radius, then merges and compresses these rings to form the ST plasma. This method is used to form MAST plasmas (see below).

Merging Compression provides a valuable saving of central solenoid flux, which can then be used to further ramp up the plasma current and/or maintain the required current flat-top.

Current is ramped down to zero in the P3 coil pair; plasma rings form around the P3 coils.