  We demonstrate practical accelerating gradients on a superconducting
radiofrequency (SRF) accelerator cavity with cryocooler conduction cooling, a
cooling technique that does not involve the complexities of the conventional
liquid helium bath. A design is first presented that enables conduction cooling
an elliptical-cell SRF cavity. Implementing this design, a single cell 650 MHz
Nb3Sn cavity coupled using high purity aluminum thermal links to a 4 K pulse
tube cryocooler generated accelerating gradients up to 6.6 MV/m at 100% duty
cycle. The experiments were carried out with the cavity-cryocooler assembly in
a simple vacuum vessel, completely free of circulating liquid cryogens. We
anticipate that this cryocooling technique will make the SRF technology
accessible to interested accelerator researchers who lack access to full-stack
helium cryogenic systems. Furthermore, the technique can lead to SRF based
compact sources of high average power electron beams for environmental
protection and industrial applications. A concept of such an SRF compact
accelerator is presented.
