  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.
