  Electron cloud beam instabilities are an important consideration in virtually
all high-energy particle accelerators and could pose a formidable challenge to
forthcoming high-intensity accelerator upgrades. Dedicated tests have shown
beampipe coatings dramatically reduce the density of electron cloud in particle
accelerators. In this work, we evaluate the performance of titanium nitride,
amorphous carbon, and diamond-like carbon as beampipe coatings for the
mitigation of electron cloud in the Fermilab Main Injector. Altogether our
tests represent 2700 ampere-hours of proton operation spanning five years.
Three electron cloud detectors, retarding field analyzers, are installed in a
straight section and allow a direct comparison between the electron flux in the
coated and uncoated stainless steel beampipe. We characterize the electron flux
as a function of intensity up to a maximum of 50 trillion protons per cycle.
Each beampipe material conditions in response to electron bombardment from the
electron cloud and we track the changes in these materials as a function of
time and the number of absorbed electrons. Contamination from an unexpected
vacuum leak revealed a potential vulnerability in the amorphous carbon beampipe
coating. We measure the energy spectrum of electrons incident on the stainless
steel, titanium nitride and amorphous carbon beampipes. We find the electron
cloud signal is highly sensitive to stray magnetic fields and bunch-length over
the Main Injector ramp cycle. We conduct a complete survey of the stray
magnetic fields at the test station and compare the electron cloud signal to
that in a field-free region.
