Abstract
Recent measurements of the H− beam current show that SNS is injecting about 55 mA into the
RFQ compared to ∼45 mA in 2010. Since 2010, the H− beam exiting the RFQ dropped from
∼40 mA to ∼34 mA, which is sufficient for 1 MW of beam power. To minimize the impact of
the RFQ degradation, the service cycle of the best performing source was extended to 6 weeks. The
only degradation is fluctuations in the electron dump voltage towards the end of some service cycles,
a problem that is being investigated. Very recently, the RFQ was retuned, which partly restored
its transmission. In addition, the electrostatic low-energy beam transport system was reengineered
to double its heat sinking and equipped with a thermocouple that monitors the temperature of the
ground electrode between the two Einzel lenses. The recorded data show that emissions from the
source at high voltage dominate the heat load. Emissions from the partly Cs-covered first lens cause
the temperature to peak several hours after starting up. On rare occasions, the temperature can also
peak due to corona discharges between the center ground electrode and one of the lenses.
