Testing of the 2.6 GHz SRF Cavity Tuner for the Dark Photon Experiment at 2 K

TL;DR

This paper reports on the testing and modification of a piezo-based tuner for 2.6 GHz SRF cavities used in dark photon searches at 2 K, highlighting improvements in tuning performance under cryogenic conditions.

Contribution

It introduces a modified tuner design with brass rods and Belleville washers to enhance force delivery to piezos in a cryogenic environment, enabling precise frequency tuning.

Findings

Successful tuning at 2 K with the modified design

Enhanced force delivery to piezos through design modifications

Demonstrated effective frequency matching for dark photon search cavities

Abstract

At FNAL two single cell 2.6 GHz SRF cavities are being used to search for dark photons, the experiment can be conducted at 2 K or in a dilution refrigerator. Precise frequency tuning is required for these two cavities so they can be matched in frequency. A cooling capacity constraint on the dilution refrigerator only allows piezo actuators to be part of the design of the 2.6 GHz cavity tuner. The tuner is equipped with three encapsulated piezos that deliver long and short-range frequency tuning. Modifications were implemented on the first tuner design due to the low forces on the piezos caused by the cavity. Three brass rods with Belleville washers were added to the design to increase the overall force on the piezos. The testing results at 2 K are presented with the original design tuner and with the modification.