Design of planar millimeter-wave metallic structures for Wakefield acceleration

Linear accelerators operating at millimeter or sub-terahertz frequencies and short pulse duration have the advantages of lower power consumption and high repetition rate. In this paper planar metallic accelerating structures with different modes operating at 210 GHz were designed. A tolerance study was also carried out to determine the sensitivities of the geometric parameters to the wakefield acceleration performance. The generated Wakefield was simulated using the beam parameter of the Compact Linear Advanced Research Accelerator (CLARA) test facility at Daresbury Laboratory. For a 55 MeV single electron bunch with charge of 250 pC and a bunch length of 0.27 mm (0.9 ps), an equivalent acceleration gradient of 20 MV/m was achieved in the simulation. The relatively modest acceleration gradient was limited by the charge in a single bunch. The acceleration gradient could be further improved by using a bunch train which has larger total bunch charge. From the simulation, the acceleration gradient of 100 MV/m can be generated when it is driven by a 10-bunch beam train.