Hieronymous Glim is an NPC who can be found in the Seven Suns Coster Market in Protector's Enclave. He is the Salvage Trader, who informs you about the salvaging process. He is also the NPC to turn in the quest Salvage Operation, which introduces the salvage system in Neverwinter.
I know obtaining such powerful magic items is not easy, so I am willing to pay for such valuable salvage with Rough Astral Diamonds.
Open your inventory and right-click on an epic magic item - this will bring up the item options menu. If you are standing within the salvage area and an item is eligible for salvage, the "Salvage" option will be available.
Clicking on the Salvage option will bring up a window showing you the Rough Astral Diamonds you will get in exchange.