The load coil, which is either an integral part of the RF oscillator circuit (free-running generator) or part of the tuning network in a crystal-controlled oscillator system, usually consists of two to three turns of 3-nimdiametercopper tubing wound in about a 3-cm-diameter spiral.
Cooling liquid or gas is circulated through the coil to dissipate thermal energy, which minimizes distortion of the coil from overheating.
The coil serves as an antenna to produce an electromagnetic field, which sustains the plasma.
It can be thought of as the "primary" winding of a RF transformer, with the "secondary" winding being the plasma itself, thereby transferring energy to maintain the plasma.
The load coil is usually grounded to earth potential at its front turn (closest to end of torch), rear turn (closest to the sample injector), or center turn. The grounding location influences the formation of a residual secondary discharge at the plasma sampling interface, which can have an significant impact on the formation of molecular oxide and doubly charged ion species in the ion beam of the mass spectrometer.
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