Q1(f). Generation of the plasma in the ICP torch

Answer in brief

Argon flowing through a quartz torch inside a radio-frequency coil is seeded with electrons by a Tesla spark; the oscillating magnetic field drives them, and collisions ionise and heat argon to a 6000–10 000 K plasma.

Key points

• Torch: three concentric quartz tubes carrying argon, inside a water-cooled copper induction coil fed by an RF generator (27.12 or 40.68 MHz, 1–2 kW).
• The RF current sets up an oscillating magnetic field; argon is a non-conductor, so it is first seeded with electrons by a Tesla-coil spark.
• The field accelerates electrons in closed circular paths (eddy current); collisions ionise argon, Ar + e⁻ → Ar⁺ + 2e⁻: an avalanche, with ohmic heating.
• The discharge is self-sustaining by inductive coupling, without electrodes: a toroidal plasma, core about 10 000 K, viewing zone about 6000 K.
• Outer argon 10–20 L min⁻¹ flows tangentially and keeps the plasma off the quartz wall; nebuliser argon carries the sample aerosol.