<title>Miniature closed-cycle cooler for FPA detectors</title>

Abstract

The various types of the Focal Plane Array JR detectors presently in development or under production are characterized by their relatively large size compared with the traditional discrete element detectors. Most of these FPAs contain "on-board" signal processors allowing the number of electrical leads to the cooled detectors plane to be independent of the number of pixels in the array. In general, the total heat load of such detectors is 1.5 -2.0 times larger than an equivalent discrete element type detector assembly.On the other hand, the size of these FPA's dictates the thermal mass of the detector array itself, and in particular when the whole detector/cooled radiation shield/cold optics is considered to be of an order of magnitude larger than an equivalent discrete elements detector assembly. This fact causes the cooldown time requirement to be the lead factor when cooling power is considered, rather than the steady state heat load.In order to achieve miniaturization, low input power and fast cooldown time, a combined team of Cincinnati Electronics, Mason, Ohio and RICOR Ltd., En Harod, Israel are working on the development phase of an integral cooler/dewar assembly -IDCA, specially tailored for FPA type detectors.The design concepts, technical parameters and some experimental test results are presented. L INTRODUCTIONThe present trend in the in&ared thermal imaging field is towards an electronically scanned. system based on a focal plane array of 2D-IR detectors. About 10 IR detector houses (mostly in the USA) are in the final development stage of various types of IR FPA detectors, mainly Platinum Silicide (PtSi) and Indium Antimonide (InSib) for the 2 to 5 im spectral window and MCT (Mercury Cadmium Telluride) for the 8-12 .tm spectral window. The predicted rate of growth of sales of this kind of detector is estimated to be 10 to 15% per annum during the next 5 to 10 years.The FPA detectors in general are characterized by a significant larger size and thermal mass than the traditional discrete element detectors. Usually they contain "on-board" signal processors. The size and thermal mass impact is most significant in the radiation shield/cold optics subassembly.A survey was carried out this year, where inputs from 7 manufacturers were analyzed, has led to the conclusion that, in general, the total thermal mass is about an order of magnitude larger than the typical mass of presently used discrete element JR detectors, the heatload, however, is only 50 to 100% larger than in the present detectors. Due to this ratio (thermal mass:steady state cooling power) the cooldown time requirements dictate the cooler's cooling power (and indirectly its size, weight and input power) rather than the actual steady state heat load. THE PROPOSED DESIGN CONCEPTDue to the fact that the total thermal mass and the cooldown time requirements dictate the cooler's cooling power (and indirectly its input power, size, weight, etc.), the proposed design concept attacks this problem in the following directions:A. The integral dewar coo...