Onomatopoeia are commonly equated to phonomimes but can also include phenomimes and psychomimes. Phonomimes are meant to imitate an actual sound - like "bark" for a Dog (wanwan in Japanese). Most Japanese onomatopoeic expressions come in the double form (the sound repeated twice). There are of course っと and り forms of onomatopoeia but the double form is probably the most common and among the most known ones.

Phenomimes are onomatopoeia that depict something closer to an action than a sound - for example "powering up" (can't recall this one sorry) or "to be spinning around" (guruguru).

Doubled base onomatopoeia are not unique to Japanese either. Think of "bam-bam", "pop-pop", "click-click", "chirp-chirp", "oink-oink" or a bit less strictly "rattattat". I believe the technical linguistic term for this is called reduplication.