Operational experience with the ELENA ion source

The Extremely Low ENergy Antiproton (ELENA) is a compact ring that was recently installed to complement the antimatter factory at CERN. A local H$^{−}$/p source is connected to ELENA for commissioning purposes of the ring and subsequent electrostatic transfer lines toward experiments, allowing to progress with the commissioning phase also in the absence of antiprotons. The ELENA source can produce pulses of H$^{−}$, with a length of a few µs and an intensity of approximately 50 µA at 100 keV, to mimic the antiproton pulse at extraction energy. In addition, the source can deliver proton pulses, if need be. After a few years of operation, several observations have been collected that will be presented in this work. Of particular interest is the observation of a fast (about 1 MHz) intra-pulse instability for H−, which resulted in poor intensity stability of the H$^{−}$ beam injected into ELENA. Possible ways of stabilising the beam pulse have been found and will be presented. The 100 kV High Voltage (HV) insulation transformer turned out to be the most critical component of the source hardware. The original transformer suffered from insulation degradation over time and several iterations were necessary to build a reliable solution, for which details will also be presented.