NOVELTY - Apparatus, comprises: chamber (14) having conducting cylindrical portion, inlet (16) and outlet for fluid; conducting shaft (30) disposed collinearly with axis of cylindrical portion of chamber and having open and closed ends; conducting pin electrode (34) having bore, first and second ends, and frit; non-conducting cylinder; means for rotating shaft; means for introducing fluid into inlet of chamber; means for introducing chosen gas into open end of shaft; and means for applying a voltage to the shaft for initiating and maintaining plasma discharge.    USE - The apparatus is useful for removing materials from a fluid (claimed), where the materials include contaminants e.g. pesticides, organic pollutants, personal care products, pharmaceuticals and pathogens. The apparatus is used in drinking water treatment and waste water treatment including industrial wastewater treatment, pretreatment to reduce biofouling in reverse osmosis systems, treatment of wastewater from military forward operating bases, water treatment in disaster recovery situations, organic phosphorus removal from wastewater treatment effluent, dissolved organic carbon removal from mine drainage, treatment of halogenated compounds solvated in aqueous industrial waste streams, treatment of high biological oxygen demand effluent from digesters associated with various biorefining processes and on-site treatment of wastewater separated from oil and natural gas production wells.    ADVANTAGE - The apparatus is a high density plasma reactor which provides purification of fluids without the need for added chemicals, without the formation of toxic byproducts and with significant immunity to changes in the quality of the raw water.    DETAILED DESCRIPTION - Apparatus, comprises: a chamber (14) having a conducting cylindrical portion having an axis, inlet (16) at one end and outlet at opposite end for the fluid; an elongated hollow, electrically conducting shaft (30) rotatably disposed collinearly with the axis of the cylindrical portion of the chamber and having open and closed ends, where the closed end facing the end of the chamber has the inlet for the fluid; at least one conducting pin electrode (34) having a bore through it, a first and a second end, and a frit (for generating bubbles) disposed in the bore in the vicinity of the first end of it, the second end is mounted through the surface of the shaft so that the bore of the pin electrode is in gaseous communication with interior of the hollow shaft; a non-conducting cylinder having an axis collinear with the axis of the chamber and interior through which a portion of the pin electrode extends, the non-conducting cylinder rotating with the shaft; means for rotating the shaft; means for introducing the fluid into the inlet of the chamber so that the fluid flows axially in the cylindrical portion of the chamber; means for introducing a chosen gas (28) into the open end of the shaft at a pressure so that gas bubbles exit through the frit of the pin electrode and rise in a countercurrent manner to the flow of the fluid; and means for applying a voltage to the shaft effective for initiating and maintaining a plasma discharge between the first end of the pin electrode and the interior of the conducting cylindrical portion of the chamber.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a tubular high-density plasma reactor.    Chamber (14)    Inlet (16)    Chosen gases (28)    Conducting shaft (30)    Pin electrodes (34)