So... we have had this on-going problem with intense Mg beam coating our optics. Keerthi found a good recipe last week with PE on and a somewhat large support gas flow. We have been running with several tens of nA since. Since yesterday's trip, I have been gradually lowering the PE from my initial value of 100V to 30V presently with about 10nA on FC6. Beam looks like it will be very stable, and the EE will maintain indefinitely like this. The first test: Marco just made overtures to use the beam for checking TIGRESS tune.