Demonstration of high-gradient electron acceleration driven by subnanosecond pulses of Ka-band superradiance
N. S. Ginzburg, A. É. Fedotov, Sergey Kuzikov, K. A. Sharypov, V. G. Shpak, S. A. Shunaĭlov, A. А. Vikharev, M. I. Yalandin, I. V. Zotova
Abstract
We report the high-gradient acceleration of electrons driven by a subnanosecond pulse of Ka-band Cherenkov superradiance (SR). The experiments are carried out in a combined ``generator-accelerator'' scheme, powered by two electron beams from a coaxial explosive-emission graphite cathode. The outer tubular beam ($\ensuremath{\approx}300\text{ }\text{ }\mathrm{keV}$; $\ensuremath{\approx}2.3\text{ }\text{ }\mathrm{kA}$) propagates along the periodic slow-wave structure (SWS) and generates a backward moving gigawatt-level SR pulse, which pumps a low-Q ``pill-box'' resonator located at the SWS input. The inner paraxial test beam ($\ensuremath{\approx}250\text{ }\text{ }\mathrm{keV}$; $\ensuremath{\approx}150\text{ }\text{ }\mathrm{A}$) passes through a hole in the resonator wall and is accelerated in extreme SR fields exceeding $500\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. The energy of accelerated electrons is estimated by measuring the test beam current after it passes through aluminum filters (foils) that absorb low-energy electrons. It is shown that the test beam contains fractions with a maximum energy of 1.25 MeV, which, taking into account the pill-box length of 4 mm, corresponds to the extremely high averaged accelerating gradient of $250\text{ }\text{ }\mathrm{MV}/\mathrm{m}$.