Development of a cryocooler conduction-cooled 650 MHz SRF cavity operating at ~10 MV/m cw accelerating gradient

TL;DR

This paper presents a novel conduction-cooling method for 650 MHz SRF cavities using a cryocooler, enabling operation at ~10 MV/m without liquid helium, suitable for industrial electron irradiation applications.

Contribution

The paper introduces a cryocooler conduction-cooling technique for SRF cavities, eliminating the need for liquid helium in industrial accelerator applications.

Findings

Achieved ~10 MV/m cw gradient on the cavity.

Demonstrated heat extraction via high purity aluminum thermal links.

Scalable approach for 1-10 MeV electron energy range.

Abstract

SRF cavities for particle acceleration are conventionally operated immersed in a bath of liquid helium at 4.2 K and below. Although this cooling configuration is practically and economically viable for large scientific accelerator installations, it may not be so for smaller accelerators intended for industrial applications such as the treatment of wastewater, sludge, flue gases, etc. In this paper, we describe a procedure to operate SRF cavities without liquid helium that can be used to construct electron-beam sources for industrial applications of electron irradiation (1-10 MeV electron energy). In this procedure, an elliptical single-cell 650 MHz niobium-tin coated niobium cavity is coupled to a closed-cycle 4 K cryocooler using high purity aluminum thermal links. The cryocooler conductively extracts heat (RF dissipation) from the cavity without requiring liquid helium around the cavity. We present construction details of this cryocooler conduction-cooling technique and systematic experiments that have demonstrated ~10 MV/m cw gradient on the cavity. By straightforward scaling up the cavity length and number of cryocoolers, the technique will provide the complete range of 1-10 MeV electron energy for industrial applications.