Beam power nonlinearity: twice the power, but not twice the neutrons?

Over the course of SNS operations, the neutronics team has observed indicators of a non-linear relationship between proton beam power and neutron brightness on multiple beamlines. As we prepare to replace the inner reflector plug, we have conducted our largest and most complete tests of this non-linearity in dedicated experiments. We will discuss our findings and subsequent experiments, their impact and our investigation of possible explanations for this behaviour. (paper)