With the recent interest in the application of nanoscale metal and metal oxide particles, there is now interest in manufacturing these materials in larger quantities. A number of techniques have evolved for the synthesis of nanopowders. For metal and metal oxide nanoparticles where coalescence is the dominating growth mechanism, concentration and the time–temperature history of the nanoparticles resulting from the reactor design determines the final particle average diameter. In this paper, we present the results of controlled synthesis of alumina nanopowder in a three-jet plasmachemical reactor, where temperature and velocity distributions are controlled by the angle of impingement of the plasma jets. The flow and temperature fields for various impingement angles were measured by an enthalpy probe. The products were characterized by means of electron microscopy, XRD analysis, and BET analysis. The dependences of particle size on the operation parameters (injection velocity of raw material, plasma jet enthalpy, solid/gas mass flow rates ratio, and impingement angle of plasma jets) are discussed. In comparison with the single jet reactor, the novel reactor can increase the production rate several times to manufacture the product with the same required surface area.