Next 2 shifts should look at fringing field in the first correct after SOL-01 (HCOR/VCOR-06). There appears to be a lot of (cruciform) distortion at large apertures (i.e. large corrector angles).
The present halo could be because of laser scattering inside the gun chamber (has the foil been removed? yes it has). The halo is more-or-less round (as seen on screen A) - it could be an image of the whole cathode (with the laser spot in the middle). The edge of the halo is the edge of the wafer?
Anode has a 20mm radius. Since the laser beam comes in at ~6 deg, the image at the cathode should be a clipped 'ellipse' shape. Maybe about half the charge is in the halo? Needs to be measured (by Steve Jamison).
Shield wall has not been replaced since removal for installation of another transfer line girder module.
Any time we get a good average current (e.g. 20 pC), then call Martin Holbourn to do some radiation measurements.
2 options - work at 250 kV to look at source of halo. Or go to 350 kV hoping that the halo will diminish, but could kill cathode. For the next 2 shifts we will therefore work at 250 kV.
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