High-power inductively coupled plasma technology is used for thermal cracking and vaporization of continuously fed carbonaceous materials into elemental carbon, for reaction with separate and continuously fed metal catalysts inside a gas-phase high-temperature reactor system operating at or slightly below atmospheric pressures. In one particularly preferred embodiment, in-flight growth of carbon nanomaterials is initiated, continued, and controlled at high flow rates, enabling continuous collection and product removal via gas/solid filtration and separation methods, and/or liquid spray filtration and solid collection methods suitable for producing industrial-scale production quantities. In another embodiment, the reaction chamber and/or filtration/separation media include non-catalytic or catalytic metals to simultaneously or separately induce on-substrate synthesis and growth of carbon nanomaterials. The on-substrate grown carbon nanomaterials are produced in secondary chambers that are selectively isolated for periodic removal of the product.