Plume Control of a Cusped Field Thruster
The cusped field thruster uses several permanent ring magnets of alternating polarity to create a multistage cusp magnetic topology. It has demonstrated a long lifetime because of reduced plasma losses to the discharge channel surface. However, the high beam divergence problem has not been solved in this type of thruster. The purpose of this technical note is to describe a plume control method to reduce its plume angle. The results show that the magnetic field intensity in the plume region and the shape of the last separatrix have great influence on plume divergence.
Preliminary Characterization of a Diverging Cusped Field (DCF) Thruster
An initial characterization of a diverging cusped field (DCF) thruster with a straight (non-diverging) discharge channel is presented. The thruster is operated on krypton propellant, at power levels ranging from 25-250 W. Thrust, specific impulse, and thrust (anode) efficiency are found to be very sensitive to cathode placement, and thrust efficiencies exceeding 20% are found over a range of operating conditions. This thruster appears to be unusually quiescent, with small amplitude (<1%), high frequency (100 kHz) fluctuations in discharge current. Plume ion current measurements indicate the existence of a conical ion emission, similar to that seen previously in a model with diverging channel walls; this suggests that the ion divergence of the plume is more closely connected to the magnetic field topography than the channel geometry. When operating with 300 V to the anode, plasma potential measurements throughout the near field reveal regions of elevated plasma potential (in some places exceeding 100 V) that are coincident with the most luminous visible regions of the discharge, where the highest ion current densities are found. In contrast, the plume electron temperature is found to peak (at more than 10 eV) along the central axis.
Optical emission spectroscopy of self-sustained magnetron sputtering
Abstract The results of plasma investigation during very high power magnetron sputtering processes are presented. Magnetron sputtering during both standard and self-sustained modes was investigated. Owing to very effective target cooling and appropriate magnetic field distribution, the high target power density could be reached (up to ∼1000 W/cm 2 , ∼1.5 A/cm 2 ). A copper target 50 mm in diameter and 7 mm in thickness was used during the experiments. Two modes of magnetron sputtering, i.e. standard and self-sustained, were investigated. Optical emission spectra were measured. The emission intensity of the Cu species as a function of target power density during both magnetron sputtering modes was observed. The spectra were observed in the 200–800 nm wavelength range. When target current rose, the emission intensity of copper ion lines increased and neutrals ones decreased.