I was cleaning up my external storage drive when I came across several SEM images that I took several years back. I decided to post this one here because it is rather self-explanatory, for most part.
This is an SEM image of a copper iris that was inside an RF cavity under very high RF field (I believe, up to 80 MV/m, if I remember it correctly). It didn't function properly, and when it was taken out, we saw pitted regions where we suspected arcing at occurred (RF vacuum breakdown). So I look at it closer under an SEM and noticed something quite fascinating that added to our body of knowledge of what went on during this breakdown event.
The picture show the region where I was focusing on, and if you look at the images, it look like water ripples coming out of a center. I saw this repeatedly at all the regions that I examined.
What we believed happened was that the bombardment of ionized gasses due to the arc had such a high energy that they melted the surface of the Cu, causing these "splash" patterns. These happened very quickly and over such a short time (at most, within half of the RF cycle, 100 picosecond time scale) that as soon as it was over, the melting stops and so the splash patterns are frozen.
It was fascinating to see many of these patterns in the pitted region of the iris.
This, BTW, is where my current avatar came from. :)
Zz.
