Nearly all plasma cutting systems fall under two categories: Conventional and Precision plasma systems. Conventional Plasma Systems - Typically use shop air as the plasma gas, and the shape of the arc is determined by the nozzle on the torch.
Generally, there are 5 popular style TIG torches - 3 air cooled & 2 water cooled (or liquid cooled as they are sometimes referred to as). Air cooled torches range up to 180 amps with a recommended max. tungsten size of 3.2mm. Water cooled torches range up to 320 amps with a recommended max.