Have disappeared after repeatedly extracting energy for gas (5)
I believe the answer is:
argon
'for gas' is the definition.
(argon is a gas)
'have disappeared after repeatedly extracting energy' is the wordplay.
I cannot really see how this works, but
'energy' could be 'go' (go can mean energy or enthusiasm) and 'go' is found in the answer.
The remaining letters 'arn' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for argon that I've seen before include "Noble gas used in light bulbs" , "noble element" , "Gaseous element" , "Noble gas, Ar" , "rare gas" .)