That's not really an effect on that song. In the recording, The Edge uses a guitar with the Fernandes Sustainer pickup in it. I believe he still uses that live, although occasionally I think he's used an Ebow. The one effect that might get you somewhat in that territory is the Auto-Volume Echo delay, but it's not quite the same. When I use that effect, I like to control the feedback parameter with the expression pedal to give me a little extra control on the length of trails. Like I said, though, it's not the same as having a sustainer or an Ebow.