Tophat logo
New Technology
TopHat in Antarctica
In order to support the measurements in the MSAM/TopHat program, we have had to develop some new technology in a number of areas. The most exciting of these are in cryogenics and the detector systems. These technologies will be useful for other measurements in the sub-millimeter wavelength range, as well as those having demanding cryogenic requirements.

In cryogenics, we have developed an adiabatic demagnetization refrigerator that can cool the detector system below 0.1 K. This design was originally developed for the SIRTF mission, and has been successfully flown on the MSAM2 flight in June 1997.

In order to cool the detector system during the TopHat mission, we needed to have a lightweight refrigerator that will cool to 0.3 K for over two weeks at balloon altitudes (approximately 120,000 feet). We have developed a special (long hold-time cryostat) to fill this need.

The TopHat detectors are monolithic silicon bolometers that are optimized for the Antarctic mission. We have also tested perforated detectors that minimize sensitivity to cosmic ray events (much lower cross section).

Concurrently, we are also developing an entirely new concept in monolithic silicon bolometers, the Frequency Selective Bolometer. This detector design allows a stack of devices to simultaneously measure a set of predetermined band passes (up to about 10). The form factor is such that an array of these devices can be packed together to form a small imaging array. For a description, download "Frequency Selective Bolometers'' M. S. Kowitt ( fsb-kowiit.pdf or