Extremely rare broadcast of Irish writer's triumph (7)
I believe the answer is:
rejoice
'triumph' is the definition.
(I know that triumph is a more specific form of be on cloud nine)
'extremely rare broadcast of irish writer's' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'broadcast of' shows a homophone (sound like) (I've seen 'broadcast' mean this (how the word might sound on the radio or TV)).
'irish writer' becomes 'joyce' (James Joyce).
'rare' with its middle taken out is 're'.
'joyce' sounds like 'joice'.
're'+'joice'='REJOICE'
(Other definitions for rejoice that I've seen before include "Show great elation" , "Exult, show great joy" , "Show great delight" , "Be exultant and glad" , "Exult -- make merry" .)