EXPERIMENTAL CHARACTERIZATION OF THE "FIRST PULSE" E-P INSTABILITY AT THE LANL PSR

A puzzling aspect of the e-p instability at PSR is the "1st Pulse" instability phenomenon. It shows up on the first beam pulse after a beam-off period of a few minutes or more. This pulse has a significantly lower instability threshold than beam pulses at regular repetition rate with a much shorter time separation. While the standard PSR operation for the Lujan Center spallation neutron source is unaffected by this phenomenon, it does interfere with some high intensity, single pulse experiments using PSR beam to another external beam area (WNR). We summarize the present experimental data characterizing this phenomenon as compared with the typical e-p instability observed at higher repetition rates and suggest some possible explanations. st pulse