Sodium converted into aluminium is helping right away with public ownership (15)
I believe the answer is:
nationalisation
'public ownership' is the definition.
'sodium converted into aluminium is helping right away' is the wordplay.
'sodium' becomes 'na' (chemical symbol).
'converted' is an anagram indicator.
'aluminium' becomes 'al' ('Al' can be a synonym of 'aluminium').
'helping right away' becomes 'ation' (I am not sure about this - if you are sure you should believe this answer much more).
'into' is an anagram of 'tion'.
'na'+'tion'+'al'+'is'+'ation'='NATIONALISATION'
'with' is the link.
(Another definition for nationalisation that I've seen is " State control".)