Thanks to ilbasso over at unmannedspaceflight.com for posting a link to this cool video showing what happens when you point a particle beam (a small one) at a Webcam. And before you get too excited, the Webcam doesn't blow up or anything -- but what happens is quite educational!
What you see is lots of little white "snow" dots appearing on the video image, speckles indicating where hits by protons briefly excited the detectors within the Webcam. Once in a while, a hit is powerful enough that it causes permanent damage to the Webcam's detector (these are helpfully called out in the animation). This is closely analogous to what happens when cosmic rays, or protons within a magnetic field, strike the sensitive detectors of space cameras. Most of the time, you get a bright dot or streak across an image; once in a while, a hit causes permanent damage to the detector, and every image taken by the camera for the rest of the mission has a dot on it in the same spot. Here's an example of a Cassini image that shows the effects of lots of proton hits (I am guessing these mostly originate within Saturn's magnetic field).
The video was produced by the education personnel on the "Cosmic Ray Telescope for the Effects of Radiation" or CRaTER instrument on Lunar Reconnaissance Orbiter; the particle accelerator apparently belongs to the Proton Therapy Center at Massachusetts General Hospital, which is interesting in itself.
Don't forget about my fund drive -- we really need your donations! Please show my bosses that you value my work.