1. KFPA Mechanical Design and Thermal Issues
Bob Simon
CDR Jan 2009
July 27, 2019

2. Single pixel test receiver
Single feed, dual polarization
65” tall, 15” diameter
13 lbs cooled weight, 150 lbs total weight
Gapped circular wg thermal transition
Gapped WR42 sliding wg output
CTI 350 refrigerator, 4 hr cool down
Aluminized Mylar for radiation shield
Installed in a 24” dia turret hole
Will keep for use as a test bed
July 27, 2019

3. Gapped circular wg transition
0.543” diameter circular wg
0.010” thermal gap, with choke groove
Upper half at 300K, lower at 15K
Hollow, shaped G10 supports
Optimized for weight, strength, and thermal isolation
Cuming microwave PS-102 foam for vacuum seal
Cuming EccoBond 45 epoxy
3 mil Kapton vapor seal
Top piece in this view is a “dummy” top plate.
July 27, 2019

4. Gapped circular wg transition
Better than about -20 return loss
July 27, 2019

5. Gapped WR42 sliding wg output
0.360” maximum travel
Δ length from 300 to 15K: ~0.144”
Stable at final temperature
Chomerics 1285 conductive elastomer
Copper wg is epoxied through bottom plate. This eliminates o-rings and wg flanges.
Ecco-foam PS102 with 3 mil Kapton
Top portion is cooled to 50K, bottom remains at 300K. Elastomer remains at 300K, so it stays flexible. Optomized for weight, strength, and thermal isolation. Shaped, hollowed G10 rods for support ” thermal gap. Used 3M DP-460 epoxy to bond the wg to the bottom plate. This is designed for metal-to-metal bonding, and was tested for outgassing.
July 27, 2019

6. Gapped WR42 sliding wg output
The final curve is somewhere between these two curves
July 27, 2019

7. Gapped WR42 sliding wg output
We were worried about energy leaking from the wg gap and feeding back into the upper circular transition. We spent considerable time testing cross coupling between the outputs and checking that no energy was leaking out of the gap.
July 27, 2019

8. 7 feed receiver
MIC 6 turret plate which also serves as the dewar top plate. 7 individual channels. Downconverters not shown, they are external to the dewar.
July 27, 2019

9. 7 feed receiver Dual polarization, 14 IF outputs
Overall size 65” tall, 23” dia
Designed for 24” dia turret hole
90 lbs cooled weight, 280 lbs total, (est)
CTI 350 refrigerator
One pressurized radome to cover all feeds
Reinforced dewar top and bottom plates. MIC6 cast aluminum for machining stability.
Designed as a stand alone GBT receiver
Test bed for a possible 61 feed receiver
July 27, 2019

10. 7 feed receiver
Will use individual circular transitions. Parallel development of integrated circular transition.
Individual WR42 wg transitions, with parallel development of an integrated unit.
Uses light weight materials wherever possible
Existing GBT receiver power supplies will be used
Amplifier bias boards are inside the cryostat. Minimizes dewar feedthru’s. ~100 wires are needed.
The single pixel was designed with an eye toward building the 7 pixel. In the same manner, the 7 feed is being designed with an eye toward building a future 61 pixel. Wherever possible, a parallel development path is taken to explore techniques that will me required for a 61 pixel. The original turret weight spec was 3000 lbs; we are now over 6000 lbs. Each new generation of receivers seems to be more complex, ie heavier. We have looked at the current requirements, and determined the existing power supply will be adequate for the 7 feed.
July 27, 2019

11. MIC-6 Cast aluminum
MIC 6® Aluminum Cast Plate Because of its cast granular structure and stress relieving properties, MIC 6® Aluminum Cast Plate allows high-speed metal removal with little, if any, of the distortion commonly inherent in long grained wrought, flat-rolled metals. MIC 6® Aluminum Cast Plate is produced by continuous casting with each thickness individually cast. By utilizing the most recent developments in casting techniques, the molten metal is continuously fed, eliminating defects from lapses and seams. Thermal gradients are stabilized since heat is removed from both plate surfaces at a balanced rate. The employment of a SNIF filtering and degassing system ensures an end product free of voids and impurities.
6061-T6 alloy is rolled from a billet. As its machined, the stresses from the rolling mill are relaxed, so it tends to warp. The more the machining, the more warping typically.
Most cast metals have voids, an obvious problem if you are making a vacuum vessel.
July 27, 2019

12. Component status Top and bottom dewar plates: design 50% complete
Dewar cylinder and radiation shield: not started
15K and 50K cold plates: not started
Feeds: 8 complete
Phase shifters: 2 tested, 10 being fabricated
Circ to square, 45° twist: 8 each complete
OMT’s: 1 complete, (+2 brass), 7 being fabricated
Upper and lower thermal transitions: 1 each complete
Radome assembly: design 25% complete
July 27, 2019

13. Thermal issues Keep emissivity as low as possible
Cylinder is electro-polished stainless steel
Radiation shield is gold plated 3003 polished aluminum. Tied to 50K stage.
Dewar wiring
Lakeshore Manganin for all dewar wiring
34 and 36 AWG, longer lengths
Electropolishing minimizes outgassing, reduces emissivity, passivates the surface, looks better, easier to keep clean, etc is a much better thermal conductor over 6061-T6 alloy. Gold doesn’t oxidize, lowers emissivity, easy to keep clean.
From GBT experience, we’ve learned that “mean-time between refrigerator failure” is greatly extended when thermal loading is kept to a minimum.
July 27, 2019

14. Refrigerator loading 50K loading: 15K loading: 5.8W radiative
3.8W conductive
9.6W total
15K loading:
0.25W radiative
2.0Wconductive
2.25W total
July 27, 2019

15. 7 feed design challenges
Cold strapping components
Wire management
Easy maintenance of dewar components
Refrigerator access for maintenance
July 27, 2019

16. Future: 61 feeds?? …challenging issues
36” dia, 5 ft long
280 lbs cooled, 450 lbs total weight
Cryogenic cooling, CTI-1020?
Requires extensive integration of components
Thermal expansion/contraction
Power dissipation
Easy maintenance
Downconveters not shown.
July 27, 2019

17. Acknowledgements Mike Hedrick Roger Norrod Ken Ward Steve White
Mike and all the shop machinists who take a lot of pride in their work and put out excellent work
Roger. Lots of guidance with design ideas, and did a lot of the testing
Ken. Inventor models, assembly of receiver, and testing
Steve. Like Roger provided a lot of guidance along the way. Also developed a lot of thermal loading spreadsheets.
July 27, 2019

18. Questions?
July 27, 2019