High-Gradient Millimeter-Wave Accelerator on a Planar Dielectric Substrate

We report the first high-gradient studies of a millimeter-wave accelerator, employing for the first time a planar dielectric accelerator, powered by means of a 0.5-A, 300-MeV, 11.424-GHz drive electron beam, synchronous at the 8th harmonic, 91.392 GHz. Embedded in a ring-resonator circuit within the electron beam line vacuum, this structure was operated at $20\mathrm{MeV}/\mathrm{m}$, with a circulating power of 200 kW, for $2\ifmmode\times\else\texttimes\fi{}{10}^{5}$ pulses, with no sign of breakdown, dielectric charging, or other deleterious high-gradient phenomena. We also present the first measurement of the quadrupolar content of an accelerating mode.