A process for gasification of solid feed material to produce a syngas includes: providing a plasma heated carbonaceous bed in a bottom section of a reactor vessel; forming a bed of deposited feed material on top of the carbonaceous bed; reacting the feed material with hot gases rising from the bottom section; forming, in a middle section of the reactor vessel, a syngas mixture containing a varying quantity of unreacted particles of the feed material; allowing the syngas mixture to rise into a top section of the reactor vessel; and at least partially quenching, by injecting a quench fluid including water, steam, or a mixture thereof, in a second, upper part of the top section, at least some of the unreacted particles sufficiently to reduce the number of unreacted particles exiting the reactor vessel that are likely to be deposited on walls of external ductwork.