A barrel reactor (100) comprises a rotatable barrel (102)； a first roller (110) located outside of the barrel (102) and arranged to facilitate rotation of the barrel, wherein the roller (110) comprises at least part of a first electrode； and a second electrode (120). A plasma is formed between the electrodes (110, 120). The second electrode (120) may also comprise a roller and the barrel (102) may be mounted on the rollers (110, 120). The spacing between, or positions of, the electrodes (110, 120) may be adjusted so as to accommodate different barrels (102) and/or to change the plasma distribution within the barrel (102).
