This is the way modern monetary systems work (sovereign fiat money). Its healthy and totally normal. Federal debt is not debt that private citizens are liable for. A treasury security is like a CD, or savings account. Since the Federal Government Complex ( including the Federal Reserve Bank) can issue currency to infinity, there is no problem here. When a treasury security expires or is redeemed, they merely changes numbers in a spreadsheet. 99% of the time those "funds" are moved back into a new treasury security. There will always be demand for interest bearing risk free government debt.
go read http://neweconomicperspectives.org/ its all there.