A Quadrupole Mode Resonant Cavity for Non-disruptive, Single-shot Emittance Measurement

cavities installed at different phase locations in the betatron lattice can afford a means of acquiring nondisruptive, single-shot measurements of a beam’s transverse emittances [1]. The device described is basically a square copper cavity oriented at 45o at a short gap in the beampipe. It is designed to resonate in its TM220 mode at 11.424 GHz. This allows us to excite this quadrupole mode resonantly with the bunches of the NLC Test Accelerator bunch train, enhancing our signal over other cavity modes. The signal is coupled out by four irises in the sidewalls through a waveguide network that rejects by symmetry the monopole and dipole modes. We present the rf design, cold test data, and experimental results from beam tests in the NLCTA.