Thermal plasmas are generated in plasma torches by
direct current (DC),
alternating current (AC),
radio-frequency (RF) and other discharges. DC torches are the most commonly used and researched, because when compared to AC: "there is less flicker generation and noise, a more stable operation, better control, a minimum of two electrodes, lower electrode consumption, slightly lower refractory [heat] wear and lower power consumption".
Transferred vs. non-transferred There are two types of DC torches: non-transferred and transferred. In non-transferred DC torches, the electrodes are inside the body/housing of the torch itself (creating the arc there). Whereas in a transferred torch one electrode is outside (and is usually the conductive material to be treated), allowing the arc to form outside of the torch over a larger distance. A benefit of transferred DC torches is that the plasma arc is formed outside the water-cooled body, preventing heat loss—as is the case with non-transferred torches, where their electrical-to-
thermal efficiency can be as low as 50%, but the hot water can itself be utilized.
Thermal plasma DC torches, non-transferred arc, hot cathode In a DC torch, the
electric arc is formed between the
electrodes (which can be made of copper,
tungsten,
graphite, silver etc.), and the thermal plasma is formed from the continual input of carrier/working gas, projecting outward as a plasma jet/flame (as can be seen in the adjacent image). In DC torches, the carrier gas can be, for example, either oxygen, nitrogen, argon, helium, air, or hydrogen; In fact, early studies of arc stabilization employed a water-vortex. Overall, the electrode materials and carrier fluids have to be specifically matched to avoid excessive electrode corrosion or oxidation (and contamination of materials to be treated), while maintaining ample power and function. Furthermore, the flow-rate of the carrier gas can be raised to promote a larger, more projecting plasma jet, provided that the arc current is sufficiently increased; and vice versa. The plasma flame of a real plasma torch is a few inches long at most; it is to be distinguished from
fictional long-range plasma weapons. ==Gallery==