Thermally Driven Acoustic Oscillations in the NICMOS Dewar Cooling Line

The Near Infrared Camera and Multi Object Spectrometer (NICMOS) was installed aboard the Hubble Space Telescope in February 1997. This instrument contains a solid nitrogen dewar for cooling infrared detectors to a temperature of 58 K. Gaseous helium flowing through a small diameter tube internal to the cryogen tank was used to freeze the nitrogen. A sudden and significant increase in the dewar heat leak during instrument development resulted in a detailed study of the possible causes. This investigation lead to the conclusion that thermally driven acoustic oscillations caused the anomalous heat transfer.