Measurement of mean electron energies in a pulsed ECR plasma using a diamagnetic coil

The transient behaviour of the diamagnetic signals in the afterglow of a pulsed ECR discharge (in H2) excited by 2.45 GHz microwaves permits the measurement of the initial electron temperature (perpendicular to the static magnetic field direction, averaged in the radial direction) as well as the temporal decay of temperature after the end of the excitation pulse. In contrast to the use of a Langmuir double probe, which represents an alternative method in electrodeless discharges within nonconducting vessels, the interpretation of diamagnetic coil measurements is not hampered by deviations of the electron energy distribution function from equilibrium. As the Maxwellian case is approached both methods give consistent results. In the low pressure regime (up to 20 Pa) the influence of electron collisions on the plasma diamagnetism proves to be negligible. Using a diamagnetic coil it is found that electron energy densities down to 0.5 x 1018 eV m-3 are still detectable. (Author)