The present invention relates to a hollow cathode plasma source and to methods for surface treating or coating using such a plasma source, comprising first and second electrodes (1, 2), each electrode comprising an elongated cavity (4), wherein dimensions for at least one of the following parameters is selected so as to ensure high electron density and/or low amount of sputtering of plasma source cavity surfaces, those parameters being cavity cross section shape, cavity cross section area cavity distance (11), and outlet nozzle width (12).