Plazmatrons

Thermal plasma is produced by special systems known as plasma torches.

Depending on the primary energy source, which may be Direct Current, Alternating Current, or Radio Frequency, we speak of DC, AC, RF or ICP (Inductively Coupled Plasma) plasma torches.

According to their effect, Plasma torches are further divided into two types: direct effect (transferred), where the electric arc runs between one electrode and the processed material, leaving the discharge chamber of the plasma torch, and indirect effect (non-transferred), where the electric arc runs between two electrodes and does not leave the discharge chamber of the plasma torch.

A standard DC plasma torch is comprised of a cathode (made of wolfram, hafnium, zirconium or graphite) and a water–cooled copper anode formed like a nozzle. These two electrodes are separated from each other by an insulator, which also has an inlet for the carrier gas.

The carrier gas passes through the space between the electrodes and across the arc discharge created between the electrodes. The high temperature of the discharge ionizes the gas into thermal plasma. The body of the plasma torch is comprised of a cooling chamber for the cathode and anode.

Plasma torch inputs include the gas for creating the plasma, cooling water, and electrical energy from an appropriate source.

The differences between individual types of plasma torches essentially consist of the manner of stabilizing the arc discharge, the shape of the electrodes, the type of carrier gas, the manner of cooling the electrodes, and the flow of the carrier gas.

Advantages of plasma torches:

• Stable performance at various power outputs
• Easy management of power outputs with simple automation of the entire process
• Option of working with several carrier gases (air, inert gases, steam, CO and CO2, hydrocarbon gases, vapors of different liquids, nitrogen and various mixtures of these gases)
• Extremely high temperatures achieved (3,000 – 20,000°C)
• High energy density (> 100 MW/м3)
• Long lifetime of electrodes
• Tried and true construction verified in industrial conditions (metal smelting)

Auxiliary systems necessary to operate plasma torches

• Cooling system to cool the plasma torch electrodes using demineralized water, and in certain cases also to cool the electrical power sources.
• Source of working gas – This system supplies the plasma torch with the particular compressed gas (usually at 1 Mpa) required to create the plasma (depending on the requirements of the technological process) for the amount required, which may be regulated. This system is typically supplied along with the plasma torch, since coordination in the selection of the working gas and its flow rate is very important for the stable operation of the plasma torch.
• Source of electric current – – this is the basic element for managing the power output of the plasma torch. A specially designed electrical scheme ensures high arc stability at various loads. A stable arc discharge means more precise control of the entire process. Depending on the needs of particular processes, the electrical power required will range from a few kW to several MW.
• Initialization (ignition) block – the arc initialization block starts the process and automatically restarts the system if interrupted. The main element of this block is a high voltage oscillator.
• Control system – the control system serves to control the electric power source and other technological systems and monitor the process using a programmable logic controller (PLC).