Speaker
Description
We describe numerical and experimental efforts to assess the suitability of various materials for the Advanced Photon Source Upgrade (APS-U) storage ring (SR) horizontal collimators. These collimators will act as beam dumps in the event that the stored charge is lost. Of particular concern is the ultra-low emittance of the APS-U 6-GeV electron beam which, at 42-pm, is 70-fold smaller relative to the present-day APS SR. Simulations include the use of the electron-beam dynamics code ELEGANT to both model beam in the APS-U as well as generate APS-U-relevant conditions to prepare for collimator tests in the present APS. Simulations under these conditions with the particle-matter interaction code MARS, as well as simple estimates based on the stopping power, suggest that aluminum and titanium are the best candidates for the horizontal collimators. They also predict the relative importance of melting point and thermal diffusivity in the choice of material. In order to guide and verify our numerical studies thus far, an experiment was conducted in the present APS to compare the effects of beam dumps on both materials. In addition to the usual suite of diagnostics including BPMs and current monitors, the experiment employed fast loss monitors for turn by turn tracking and a visible-light camera for online imaging of the collimator surfaces. A postmortem microscopic examination of the surfaces was also conducted. The results of both numerical and experimental studies will be presented.