3rd arm do not work well under this configuration because of the local dump. During a test we took last night, 3rd arm will record a trigger rate of 5k at 50nA, 30k at 70nA, 100k at 100nA. It is not linear, and we are still trying to understand this. But for now we could still get some information form 3rd arm rate: if the 3rd arm rate is much high than the above values at the corresponding beam current, it suggests the beam is hitting something other than local dump, the shift crew should run a spot_3 to check the beam position and raster size.