• C.-J. Jing
  Euclid TechLabs, LLC, Solon, Ohio
• S.P. Antipov, M.E. Conde, W. Gai, F. Gao, J.G. Power, Z.M. Yusof
  ANL, Argonne
• H. Chen, C.-X. Tang, S.X. Zheng
  TUB, Beijing
• P. Xu
  Tsinghua University, Beijing

Wakefield excitation has been experimentally studied in a 3-cell X-band standing wave Photonic Band Gap (PBG) accelerating structure. Major monopole (TM01- and TM02-like) and dipole (TM11- and TM12-like) modes were indentified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be ~10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to ~30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.