The present invention is an improved design and operation of a short contact time Fluid Catalytic Cracking (FCC) Reactor wherein the upper internal riser and a lower internal riser are in fluid connection with one another and provide an improved disengaging zone for entraining the vapors from the dilute phase area of the FCC reactor. Detailed preferred embodiments include improvements over the prior art to the internal central riser, riser termination apparatus, cyclone separators, and a coke mitigation baffle system, as well as associated improved fluid catalytic cracking processes utilizing the novel reactor design.