Development Of A Compact Photo-injector With RF-focusing Lens For Short Pulse Electron Source Application

TL;DR

This paper presents the design, simulation, and testing of a compact RF-driven photo-injector with RF focusing for ultrafast electron sources, achieving high power and precise control over electron bunch parameters.

Contribution

It introduces a novel compact RF-gun design with RF focusing, combining comprehensive modeling and experimental validation for ultrafast electron source applications.

Findings

Achieved peak RF power > 5 MW with tested klystron system.

Generated electron bunches of 100fC to 1pC with pulse durations of 30 fs to 1 ps.

Demonstrated effective RF acceleration and focusing of electron bunches.

Abstract

For development of compact ultrafast electron source system, we are currently designing a short-pulse RF-gun with RF focusing structure by means of a series of comprehensive modeling analysis processes. EM design of a 2.5 cell resonant cavity with input coupler, acceleration dynamics of photo-emitted electron bunch, EM design of RF-lens with input coupler, and phasespace analysis of focused electron bunch are systematically examined with multi-physics simulators. All the features of the 2.856 GHz cavity geometry were precisely engineered for acceleration energies ranging from 100 keV to 500 keV (safety limited) to be powered by our 5 MW S-band klystron. The klystron (Thales TH2163) and modulator system (ScandiNova K1 turnkey system) were successfully installed and tested. Performance tests of the klystron system show peak output power > 5 MW, as per operation specifications. At the quasi-relativistic energies, the electron source is capable of generating 100fC -- 1 pC electron bunch with pulse duration close to 30 fs -- 1 ps and transverse size of a few hundred microns. PIC simulations have shown that the electron bunch undergoes fast RF acceleration, rapidly reaching the desired energies, which can be controlled by tuning RF injection phase and input driving power. It has been shown that it is possible to also focus/compress the bunch longitudinally using a RF-lens, which would allow us to control the temporal resolution of the system as well. While our primary analysis has been performed on a 2.5 cell design, we are also looking into half-cell (single cavity) design that is expected to provide the same range of beam energy with a simple configuration.