The IMACS dewar was designed, fabricated, and assembled by Gerry Luppino (UH IfA) and GL Scientific, Honolulu, Hi.
The IMACS dewar incorporates several interesting features. Although no longer unusual for its size, the dewar contains 8 SITe 2K x 4K pixel CCDs, arranged to form a 8K x 8K pixel focal plane array. The individual detectors will be aligned and coplanar to a few microns. The array is cooled by a pair of APD CryoTiger closed-cycle coolers, which eliminate the need for liquid nitrogen. The focal plane array sits on a commercial, Physik Instrument X-Y stage, which provides +/- 100 microns of array position control for removing the effects of gravitational flexure. Finally, the array and X-Y stage sit on a large titanium flexure stage, which provides +/- 1 mm of focus control.
Current flexure testing shows that the focal plane, when properly balanced, flexes about 10 microns in the X direction, and 0 microns in the Y direction, for 180 degree rotations of the dewar about the optical axis. Cooling tests completed 10/26/00 showed that the focal plane takes about 4 hours to stabilize at -122 C.
The latest assembly and testing images are shown below.
The dewar undergoing vaccuum pumping. Note connectors
for detector focus encoder, motor, and
limit/home switches. Also Cryotiger hose connection protectors. And posts for interface to dewar
lifting fixture. Note location of vac valve and vac. gauge to cryotigers.
Off side showing lift fixture post, vac gauge, handles, focus limit assembly, SA controller and mounts.
7/10/02 - The IMACS 8K array, full-up with array controller (blue box at left), twin cryotigers (at right). The dewar currently has 4 of the 8 CCDs installed. Cooling tests and dark testing are under way.
7/10/02 - Dewar assembly and the two cryotiger compressors. Much longer hoses will be used at the telescope.
Greg Burley waits patiently for the cryotigers to cool the dewar down...
Ian Thompson assembling the CCDs on the mosaic base plate.
Four down, four to go...
CCD array being assembled under the Keyence displacement sensor.
Bigelow and Thompson measuring flatness of the array relative to the dewar mounting plate.
End view of the IMACS 8K controller.
Interior showing instruments for measuring flexure of the focal plane array.
Cryotiger and getter
Focal plane assembly showing G10 truss, invar mounting plate, and copper cooling straps.
Dewar interior showing cooling strap connection between buss bar and array.
Dr. Luppino wires up the RTD's prior to cold testing.
RTD on lower right boat can just be seen.
Dewar re-assembled with Cryotigers plumbed to their compressors.
Cooling test set-up.