These results are for the time period 2013-2014 after upgrades to the instrument
In early 2013 the VPPEM was extensively upgraded. The original vacuum chamber, which was
found to be magnetic was distorting the image, and was replaced by an all aluminum
chamber with titanium conflats.
The pure iron ring which is the field termination aperture was sent to have a very soft magnetic
A sample introduction system was added with extra pumping, and an ion cleaning gun. The
CHA input and output lenses were changed to give greater flexibility with magnification.
The image detector was changed to a larger microchannel plate/phosphor detector which
uses a fiber optic vacuum window.
These and other changes gave an immediate improvement in resolution.