Experiments On A Conduction Cooled Superconducting Radio Frequency Cavity With Field Emission Cathode

TL;DR

This paper explores a conduction-cooled superconducting RF cavity with a field emission cathode aimed at generating high-repetition-rate electron bunches, demonstrating initial gradients and quality factors with potential for improved performance.

Contribution

It presents the development and experimental results of a conduction-cooled Nb3Sn SRF cavity with a field emitter, a novel approach for high-frequency electron injection.

Findings

Achieved 0.4 MV/m average gradient with a quality factor of 1.4 x 10^8.

Limited by RF power input and coupling efficiency, but potential for higher gradients.

Demonstrated feasibility of conduction-cooled SRF cavity with field emission for high repetition-rate applications.

Abstract

To achieve Ampere-class electron beam accelerators the pulse delivery rate need to be much higher than the typical photo injector repetition rate of the order of a few kilohertz. We propose here an injector which can, in principle, generate electron bunches at the same rate as the operating RF frequency. A conduction-cooled superconducting radio frequency (SRF) cavity operating in the CW mode and housing a field emission element at its region of high axial electric field can be a viable method of generating high repetition-rate electron bunches. In this paper, we report the development and experiments on a conduction-cooled Nb3Sn cavity with a niobium rod intended as a field emitter support. The initial experiments demonstrate 0.4 MV/m average accelerating gradient, which is equivalent of peak gradient of 3.2 MV/m. The measured RF cavity quality factor is 1.4 x 108 slightly above our goal. The achieved field gradient is limited by the relatively low input RF power and by the poor coupling between the external power supply and the RF cavity. With ideal coupling the field gradient can be as high as 0.6 MV/m still below our goal of about 1 MV/m.