Measurements of inductively coupled plasma temperatures: comparison of N2+ rotational temperatures with optical pyrometry

Inductively coupled plasma (ICP) temperatures were measured using both N2+ spectral line intensity and optical pyrometry. The forward power output of the r.f. generator was varied between 0.75 and 2.00 kW in increments of 0.25 kW. Dry nitrogen was introduced into the plasma through the central gas (carrier gas) inlet at a flow rate of 0.5 dm3 min–1. A pyrolytic graphite probe with a melting-point of 3900 K was positioned 15 mm above the load coil in the centre of the plasma. The temperatures measured with the pyrometer were between 1700 and 2200 K for the power outputs mentioned above. The temperatures calculated from the slopes of the Boltzmann distribution plot (spectral line intensity versus the quantum numbers) are comparable to the pyrometric readings. Results obtained by the optical pyrometry method show that the ICP temperature is linearly dependent on the forward power of the r.f. generator.