A diagnostic neutral beam (DNB) is used in the Tokamak Fusion Test Reactor (TFTR) to provide a time-modulated, spatially localized enhancement of the signal in the charge-exchange (CX) diagnostic. Two autonomous charge-exchange neutral analyzer (CENA) systems have been designed f or the TFTR. The first system measures the plasma ion temperature along as many as 12 vertical line-of-sight chords spaced approximately equidistantly across the torus minor diameter. The second system emphasizes the measurement of ion phenomena associated with neutral beam injection heating and has a fanlike field of view along six sightlines in the equatorial plane. The DNB is steerable in order to access the viewing field of either CENA system. The performance of the DNB is evaluated to determine the optimal beam parameters for active CX measurements. Using the optimal beam design parameters, the effectiveness of the neutral beam doping is examined for both CENA systems over the envisioned range of the plasma density and temperature in TFTR.