  One of the on-going issues with the use of microchannel plates (MCP) in the
ionization profile monitors (IPM) at Fermilab is the significant decrease in
gain over time. There are several possible issues that can cause this.
Historically, the assumption has been that this is aging, where the secondary
emission yield (SEY) of the pore surface changes after some amount of extracted
charge. Recent literature searches have brought to light the possibility that
this is an initial 'scrubbing' effect whereby adsorbed gasses are removed from
the MCP pores by the removal of charge from the MCP. This paper discusses the
results of studies conducted on the IPMs in the Main Injector at Fermilab.
