Initial longitudinal diagnostics for ELENA’s commissioning

CERN’s Extra Low ENergy Antiproton (ELENA) ring underwent its second full year of beam commissioning in 2018 and succeeded in decelerating more than 1 E7 antiprotons to extraction energy. Traditional DC beam transformers do not work at ELENA’s low intensity hence alternative measurements methods, described in this note, were embedded within ELENA’s Low-Level RF (LLRF) system. These longitudinal diagnostics have provided to the users the measured bunched beam intensity and bunch length as Oasis signals. Derived from longitudinal and from transverse pick-up signals, the longitudinal diagnostics were used to ascertain and estimate progress with the machine transmission efficiency. This note describes the digital signal processing implementing the longitudinal diagnostics deployed in the 2018 ELENA run. Some challenges encountered and the beam results obtained are shown. Initial tests for de-bunched beam measurements based upon Schottky scans are also mentioned. Finally, details on the system upgrade that will take place during Long Shutdown 2 (LS2) are given.