West perhaps contributes to plasma engine (3)
I believe the answer is:
mae
'west perhaps' is the definition.
(actress Mae West)
'contributes to plasma engine' is the wordplay.
'contributes to' indicates a hidden word (I've seen 'contributing to' mean this (the answer contributes to part of the clue )).
'MAE' can be found hidden inside 'plasma engine'.
(Other definitions for mae that I've seen before include "more Scots" , "- - West, movie vamp" , "- West, US film actress" , "- - West, life-jacket" , "-- West, C-twenty actress" .)