In this paper the novel technique of THz time domain spectroscopy has been applied to obtain time-resolved measurements of the plasma density in the active zone of a HiPIMS discharge with a titanium target. The obtained peak values are in the range of 10 12 -10 13 cm −3 for discharge current densities of 1 to 4 A/cm 2 at 0.5 and 2 Pa argon pressure. The measured densities show good correlation with the discharge current and voltage and the intensity of various atomic and ionic lines. The well known phases of the discharge have been identified and related to the variation of the electron density. The measurement results show that the plasma density remains nearly constant during the runaway/self-sputtering phase. Based on that it is conjectured that singly charged titanium ions are the dominant ion species during this phase.

The effect of a weak rotating magnetic field on an ECR discharge plasma in argon has been investigated. The field was produced by an arrangement of bars surrounding the discharge vessel and carrying harmonic currents appropriately shifted in phase. Optical probes, Thomson scattering, Li beam diagnostics and a fast CCD camera were used for the investigations. A significant modulation of the electron density and temperature at the plasma edge was observed. This can be assigned to an increase of the transport of electrons to the discharge vessel walls where the lines of the total B field cross them. Alteration of the transport conditions results in perturbations, which diffuse radially inwards at a velocity corresponding to that of the Bohm diffusion. A pattern of light emission develops, which rotates synchronously with the rotating field. Correlation between the total light emission from different plasma volumes was determined based on measurements made with optical probes. This shows fluctuations propagating azimuthally, anticlockwise with respect to the direction of the main B field, with a wavelength of about (7-10) × 10 −2 m. These fluctuations exist independently of the presence of the rotating magnetic field. Further investigations are still needed to answer two key questions: does the plasma rotate as a whole or is the observed effect a rotation of the plasma state only, and how does the rotating field affect fluctuations at the plasma edge?