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

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

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

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

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. 0.010” 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

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

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

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

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

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

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

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

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. 3003 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

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

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

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

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

Questions? July 27, 2019