Anomalous temperature and amplitude-dependent performance characteristic of a 1000W/80K coldfinger

A large acoustic-Stirling (‘pulse tube’) coldfinger designed for approximately 1000 W cooling power at 80 K has shown a distinct decline in efficiency as input power is increased, especially at lower temperatures. Anomalies in the temperature profile around the regenerator circumference are found to correlate strongly with the decline in efficiency; furthermore, the temperature profile is symmetric about the axis of the side-entry transfer tube that communicates acoustic power to the coldfinger. We suspect that the vigorous flow from the transfer tube is inducing a convection cell in the regenerator itself, and that it is the large scale of this coldfinger that makes it susceptible to this type of behavior.