Source : Webster's Revised Unabridged Dictionary (1913)

Experimenter \Ex*per"i*men`ter\, n.
   One who makes experiments; one skilled in experiments. --
   Faraday.

Source : WordNet®

experimenter
     n 1: a research worker who conducts experiments
     2: a person who enjoys testing innovative ideas; "she was an
        experimenter in new forms of poetry"