2. Instrumentation

2.1 High-frequency generator and argon plasma

To create the plasma, an electric current flows through a metal induction coil surrounding a torch, generating a magnetic field (figure 1 ). This current is supplied by a generator, either a limited-life power tube or a solid-state generator. This generator is fitted with a free-running or quartz-controlled oscillator, with a frequency of 27.12 or 40.68 MHz, and is capable of delivering a power of between 600 and 1,700 W, depending on the model. To prevent overheating, the coil is hollow, with an argon or liquid coolant flowing through it.