In this document we analyze the Hall D electron beam energy during the 2016 spring run. The energy appears to drift with time, typically by tens of MeV over a day. It also sometimes jumps from one value to another within a few minutes. Overall, the Hall D electron beam energy varied by about 140 MeV during the spring run.
The Hall D beam energy is obtained from the magnetic field and the vertical beam positions in the ramp leading to the Hall D tagger. The epics name for this measurement is HALLD:p. In this document, energy instability/drift/jump refer to the value reported by this measurement. Those can be real energy changes or artifacts of the measurement. This document tries to disentangle the two possibilities.
A conclusion from this study is that epics value HALLD:p should not be use on a (slow control) event-per-event basis since it displays many outlying values that do not correspond to the actual beam energy. Rather, a database listing the approximate beam energies for given periods, and a condition that the energy does not jump too far from the approximate value, would be more adequate.
