Non-linearity discussion document.
I prepared a short document that presented my thoughts on the cause of non-linearity in the 253 and Isoprime instruments. In it I speculated that the non-linearity results from scattered components of the m/z = 44 beam interacting diirectly with the secondary electron suppression optics on the faraday cups. I also suggested that a retarding potential lens incorporated in the faraday design might well eliminate the non-linearity by cutting out the scattered component. An alternative approach, apparently used by Nu instruments is to use an electrostatic field sector to clean the beam up. That this approach seems to work strengthens my conviction that the issue is caused by a direct interaction of a scattered component of the 44 beam with the secondary electron suppression optics.
The document can be downloaded from here http://dx.doi.org/10.6084/m9.figshare.1254807