Plasma acceleration from radio-frequency discharge in dielectric capillary

A capacitive rf discharge was demonstrated in a dielectric capillary for generation of quasineutral plasma flow with energies of several tens of eV. A potential gradient at the open end of the capillary and high-temperature electrons in the capillary discharge promote the ion acceleration. The plasma flow was generated from a ceramic capillary with inner diameter of ∼0.8 mm and a length of ∼10 mm, at a gas flow rate of 2-10 SCCM (SCCM denotes cubic centimeter per minute at STP) and input power of 15-20 W. The ion energy spectrum consists of high-energy accelerated ions and a low-energy tail formed due to ionization in the acceleration region. The relatively wide plume angle of ∼65 deg. indicates that the acceleration region is placed outside the capillary and has a convex shape. Estimated total efficiency at 2 SCCM Xe flow rate and 15 W input power reaches 2%-3%. This approach may be attractive for micropropulsion applications due to its simplicity, low weight and small dimensions of the source, and the absence of a cathode neutralizer