Measurement of the Magnetic Field in a Plasma Using an Impurity Probe Spectroscopy

The magnetic field strength has been obtained from the Zeeman splitting. Thermal He atoms, as an impurity, were injected into a low density (n e∼5×1010 cm-3) hydrogen plasma produced by electron cyclotron resonance. A singlet line at 6678 Å from He atoms excited by the plasma electrons splits into a normal Zeeman triplet in the magnetic field. The line profile was measured with a high resolution Fabry-Perot interferometer. This diagnostic allows the determination of the Zeeman splitting at magnetic fields as low as 1.2 kG, lower than which the splitting is masked by the Doppler broadening of the injected atoms.