The present study adopts proton irradiation to solve the problems, such as performance degradation due to outgassing and weak adhesion, of a carbon nanotube (CNT) field emitter fabricated by the indirect coating method. The protons collide against the CNT layer and the copper film, and results in thinning out of the CNTs and particle migration of the copper constituents. This process reduces the turn-on field and increases the lifetime of CNT emitters, respectively. Numerical simulations have been performed to understand the results from experiments by using a software, SRIM 2008. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3443571]