Absolute beam position measurement in an accelerator structure

High gradient acceleration requires exquisite control of beam position relative to the accelerating structure electrical center in order to avoid the excitation of transverse deflecting fields. We have measured such “absolute” beam position in a prototype X-band accelerator structure using beam induced microwave signals. We then verified our measurements independently by probing the beam excited field with a second witness bunch. Absolute beam positioning precision has been demonstrated at the level of 40 μm.