CRJ-200 Captain reported encountering wake turbulence on arrival into ATL in trail of a B747.

Narrative

On the CHPPR arrival into ATL; we were close enough behind a 747 that we were able to identify the aircraft type by sight. In the vicinity of HIDRO on the arrival; the aircraft suddenly and abruptly rolled approximately 40 degrees to the left. The autopilot did not disconnect and adequately recovered to wings level so the pilot flying did not disconnect the autopilot but protected the yoke with his hand. I immediately contacted Atlanta Approach and told them we needed an offset. He seemed confused and reluctant; informing us that we were 8 miles in trail. I told him we were experiencing significant wake turbulence due to a 25 kt tailwind and needed a heading. At this point the aircraft rolled again; about 20 degrees to the left. He still told us all he could do was offer a lower altitude; which I refused as it would have had the potential to exacerbate the problem. I told him we needed a heading of either 130 or 180 and nothing else was acceptable; and that it was not a request. He assigned us a heading of 180. After the 747 had flown past our intended flight path we accepted a turn back towards the arrival and the remainder of the flight was uneventful. Wake turbulence from inadequate in trail spacing