Proton Beam Source Suitable for Fast Ignition Targets

A focused proton beam, which has potential to ignite fast ignition targets, is generated from a sharply defined metal-vacuum interface facing the compressed fuel kernel. Since it must be quite close (100s of $\mu$m) to that kernel to limit time spread of the proton beam, this surface must be protected from the shell implosion by a reentrant cone. The walls of that cone modify the proton beam by limiting the accelerating area and, potentially, refocusing the protons, particularly the low energy component. We have examined the effect of such walls using a test setup and will report on the results.