Rapid Pulse Detonation-seeking info

I was wondering if anyone could help me?- I have heard of he above aircraft propulsion system and the exhaust contrails looking like a doughnut on string rather than normal jet stream.I have read several reports about aurora having such and exhaust stream-
JUst before Xmas I saw two aircraft flying at high altitude over my property( a remote location -between Sydney and Brisbane on the East coast of Australia)
The first was a conventional jet airliner -maybe a 737 or something of that size-flying maybe a few minutes in front of the second aircraft- which was huge- only plane have seen before that size was a b52- It had 4 sets of engines and their exhaust trail was the donut on string ---0-----0---0
i had heard of this trail but not on a bomber sized aircraft.
Can anyone help?