I found it. It is indeed Jean Michel Jarre as Tray73 guessed.
"Rendez-Vous IV", Jean Michel Jarre
Meanwhile, I have the impression that I have seen it in a video hit not just filmage from a concert, as we can find on youtube.
I had no MTV (or any other video hits channel) at that time and so I have seen it probably on a portuguese weekly TV show with the top charts videos. It was a portuguese TV show but the videos were international. Anyway, I didn't want to say it because I thought it could be a bit misleading... But now that I found it it's ok.
Anyway, I'm pretty sure about a video with that music, as I said. It looked much more like a video hit than just a concert filmage. If you happen to know of the existence of such a video for that music, pls let me know.
But the music is definetly that: Rendez-Vous 4, by Jean Michel Jarre. It is funny how I confused that with Enola Gay...