Kamran Vaziri and Don Cossairt
Over the last few months a large group of experimenters, accelerator physicists, and radiation physicists have worked very hard to prepare for the FermiLab Director's Review of a campaign to raise the NuMI 120 GeV beam power from 400 kW to 700kW and then to 1200 kW. These beam powers are needed for the NOvA experiment. NOvA (which stands for NuMI off-axis neutrino appearance) hopes to observe muon-neutrino to electron-neutrino conversion, of importance for telling us the mass hierarchy of neutrinos as well as possibly whether there is leptonic charge-parity (CP) violation. The experiment requires a 20-25 kTon detector located off the central axis of the NuMI beam, approximately 810 km away. The off-axis location (Ash River, Minnesota) results in a neutrino peak narrow in energy distribution.
As the beam power increases, the relative importance of different radiological issues change. Repair and handling of the radioactivated components is one that needs the most attention. Dose rates up to several hundred R/hr due to long-lived radioisotopes are expected. At this level, shielded remote manipulators become very attractive. However, it is not clear whether anything more than simple repairs can be done on the complex beam devices. Of course, practice will improve these abilities, but it is not always clear at what level of repairs replacing with a spare, if available, is a better choice. The Director’s Review Team, which comprised several experts from our sister laboratories and the Department of Energy (DOE), had generally favorable and useful comments.