Third Quarter 1998

Assembly of Phase II of the cryostat was completed in early July. Flexure testing was conducted on the lift/tilt table. A maximum flexure of 75 micron at 90 degrees was measured at the extreme end of the spectrograph box in excellent agreement with the FEA prediction. Leak testing of the liquid nitrogen can revealed several leaks in some of the e-beam penetration welds. These were successfully fixed using epoxy cement but to increase confidence in the can we are planning to have it re-made with a new design which does not rely on penetration welds. Following plumbing of the compressors from the compressor room to the IR Lab the first cooldown of the cryostat was begun on September 21. The test was a complete success. With a cold mass of about 65% of the final assembly, the cold structure cooled to below 90K in 6 hours and reached an equilibrium of about 80K after 12 hours. The close-cycle cooled radiation shield fell below 140K after 24 hours and reached an equilibrium of about 115K after 48 hours. After 24 hours the hold-time on the 10-liter liquid nitrogen can was over 40 hours. The only anomaly was the 19K temperature of the second stage of the CTI 1050 closed-cycle cooler, rather than an expected temperature of less than 15K. This is possibly due to calibration of the temperature sensor.

In August, Phase IVa of the cryostat fabrication (the fore-optics mounts and image rotator assembly) was awarded to Earth, Air and Space (EAS). The remainder of the mechanical fabrication (slit-viewer, dichroic turret, prism and grating mounts, and instrument mounting box) are scheduled for fabrication in the machine shop here at the IfA. Also during August, Optics For Research delivered the AR coated lenses and windows, and Thin Film Labs delivered the dichroic beam-splitters for SpeX and NSFCAM.

Building upon experience gained with the prototype controller fabrication of slightly modified array controllers for SpeX was started during the Third Quarter. To enable higher speed read out for the newly funded high-speed spectroscopy mode a second DSP board was added to the VME64 control computer together with a second optical fiber channel, one for each DSP board, linking the cryostat mounted electronics to the computer. These modifications increased the (full array) speed from 3Hz to 10Hz.

PAIDAI members met at the Raytheon Infrared Center of Excellence (RIRCoE - formerly SBRC) in Santa Barbara on July 17 to review progress. The cold tests of the first four arrays at RIRCoE were reviewed and the order of testing at NOAO, following PED removal, was decided. By the end of September these arrays had been characterized by Al Fowler at NOAO. All four are four quadrant devices and the best, SCA47672, is one of the best Aladdin 2 arrays yet produced. SCA47672 is cosmetically good with a median dark current of about 0.2 electrons/sec and a readnoise of 40 electrons RMS. The next four arrays should be fully characterized by November. The final six 1024x1024 InSb parts will be hybridized onto Aladdin 3 readouts and the 10 week process is expected to begin in November. The first six 512x512 are currently in hybridization and should be out of the foundry and ready for testing by the end of the year. SpeX will use a 512x512 array in its slit-viewer/imager.

Photos for this quarter:

Cryostat-mounted electronics rackmount containing clock/bias, ADC, pre-amp and fiber channel boards
Big Dog computer runs the spectrogaph array. The rackmount contains a single-board SPARC computer, two DSP boards, and two fiber boards with fiber optic links to the cryostat-mounted electronics
Guide Dog computer runs the slit-viewer/imager array. The rackmount shown contains a a single-board SPARC computer, one DSP board, one fiber board, and a GPS board
Cold structure on fork lift truck.
Cold structure being moved into vacuum jacket
Cold structure bolted into vacuum jacket
Cryostat with cover removed on the lift/tilt table
Flexure testingof the cryostat on the lift/tilt table
Closed-cycle cooler and thermal connection to actively cooled radiation shield
Cryostat and cold structure showing LN2 can bolted to spectrograph box, cold mounting structure and support trusses. The active shield and vacuum jacket covers are removed.
Active shield. A view of the cryostat showing the actively cooled radiation shield which surrounds the LN2 cooled cold structure
First cooldown showing LN2 can fill and closed-cycle cooler plumbing