A manufacturing apparatus for growing silicon nanowires on carbon-based powders, comprising: an elongated low-pressure CVD chamber (100, 200); an elongated metal process tube (104, 204) positioned within the CVD chamber; one or more tumbler reactors (106, 206) removably positioned within the elongated metal process tube and configured to rotate within the elongated metal process tube, said one or more tumbler reactors configured to receive the carbon based powder, said one or more tumbler reactors each comprising an elongated cylindrical metal tube and each having a gas distribution manifold (116, 216) positioned therein and extending the substantial length of the tumbler reactor, wherein the CVD chamber comprises heating elements (108, 110, 208, 210) to heat the elongated metal process tube and the one or more tumbler reactors positioned within the elongated metal process tube, wherein the elongated metal process tube comprises a vacuum port (112, 212) for injecting purge gases and an exhaust port (114, 214) connected to a vacuum pump to provide a low pressure environment, and wherein the gas distribution manifold comprises a gas injection member (117, 217) comprising a plurality of injection ports (119, 219) positioned along the gas injection members for injecting a mixture of process gases uniformly into the tumbler reactor, and characterised in that the one or more tumbler reactors each comprise a mesh end cap and an end plate at both ends of the tumbler reactor, each mesh end cap having a plurality of apertures sized such that the apertures contain the carbon-based powder within the tumbler reactor and allow the process gases to flow between the tumbler reactor and the metal process tube. an elongated low-pressure CVD chamber (100, 200); an elongated metal process tube (104, 204) positioned within the CVD chamber; one or more tumbler reactors (106, 206) removably positioned within the elongated metal process tube and configured to rotate within the elongated metal process tube, said one or more tumbler reactors configured to receive the carbon based powder, said one or more tumbler reactors each comprising an elongated cylindrical metal tube and each having a gas distribution manifold (116, 216) positioned therein and extending the substantial length of the tumbler reactor, wherein the CVD chamber comprises heating elements (108, 110, 208, 210) to heat the elongated metal process tube and the one or more tumbler reactors positioned within the elongated metal process tube, wherein the elongated metal process tube comprises a vacuum port (112, 212) for injecting purge gases and an exhaust port (114, 214) connected to a vacuum pump to provide a low pressure environment, and wherein the gas distribution manifold comprises a gas injection member (117, 217) comprising a plurality of injection ports (119, 219) positioned along the gas injection members for injecting a mixture of process gases uniformly into the tumbler reactor, and characterised in that the one or more tumbler reactors each comprise a mesh end cap and an end plate at both ends of the tumbler reactor, each mesh end cap having a plurality of apertures sized such that the apertures contain the carbon-based powder within the tumbler reactor and allow the process gases to flow between the tumbler reactor and the metal process tube.