Simulations of currents in X-band accelerator structures using 2D and 3D particle-in-cell code

The accelerating gradient is one of the crucial parameters affecting design, construction and cost of next-generation linear accelerators. For a specified final energy, the gradient sets the accelerator length, and for a given accelerating structure (and pulse repetition rate) it determines the power consumption. Accelerating gradients in the order of 100 MV/m have been reached in short (~ 20 cm) standing wave and traveling wave X-band accelerating structures. But, recent experiments have shown damage to traveling wave accelerating structures at gradients as low as 50 MV/m after 1000 hours of operation. RF breakdown is a probable cause of this damage. An extensive experimental and theoretical program to determine a safe operating gradient for the Next Linear Collider (NLC) is under way in SLAC. The present work is a part of that program