  During the initial phase of operation, the linacs of the Next Linear Collider
(NLC) will contain roughly 5000 X-Band accelerator structures that will
accelerate beams of electrons and positrons to 250 GeV. These structures will
nominally operate at an unloaded gradient of 72 MV/m. As part of the NLC R&D
program, several prototype structures have been built and operated at the Next
Linear Collider Test Accelerator (NLCTA) at SLAC. Here, the effect of high
gradient operation on the structure performance has been studied. Significant
progress was made during the past year after the NLCTA power sources were
upgraded to reliably produce the required NLC power levels and beyond. This
paper describes the structures, the processing methodology and the observed
effects of high gradient operation.
