Corrugated Feedhorn Arrays by Additive Manufacturing

The Department of Energy’s Office of Science seeks to reduce cost and improve high energy physics particle and radiation detector sensitivity and manufacturability via the flexibility and reproducibility of additive manufacturing to produce complex detector components. Cosmic microwave background measurements characterize the temperature and polarization anisotropies of the universe. A critical component of cosmic microwave background observation is the feedhorn antenna, used to convey and focus waves onto a transition-edge- sensor bolometer operating at cryogenic temperatures. Current materials and manufacturing processes for feedhorn arrays have insufficient thermal conductivities at operating temperatures, a poor thermal expansion coefficient match to the Si detector, and are cumbersome, inefficient, and costly to manufacture. The challenges of coefficient of thermal expansion, thermal conductivity, manufacturing system complexity, and the anticipated ~500,000 cosmic microwave background detectors sets the need. This program will design, build, finish, and evaluate the performance of molybdenum feedhorn arrays for cosmic microwave background high energy physics experiments. Molybdenum has been chosen as the feedhorn material due to its coefficient of thermal expansion match with the bolometer, high thermal conductivities at 300 mK compared to coated Si platelet or Al designs, no magnetic properties, ability to be electrochemically polished, and manufacturability with electron beam powder bed fusion additive manufacturing approaches. Phase I will demonstrate the combined additive manufacturing and electrochemical polishing approaches to produce feedhorn arrays that meet stage 4 cosmic microwave background detector requirements of operating frequency, shape tolerance, thermal conductivity, and coefficient of thermal expansion match at lower manufacturing costs. This combined approach to produce feedhorns for stage 4 cosmic microwave background detectors has never been demonstrated; however, the key processes that underlie each unit operation, have been independently demonstrated by team members. Phase I will demonstrate this approach of manufacture and final finish of functional feedhorn components for stage 4 cosmic microwave background detector systems, by leveraging existing expertise in designing, building, finishing, and analyzing stage 4 cosmic microwave background detector system components. The potential cost savings of the technology versus existing processes will be estimated. Phase II will build a testable stage 4 cosmic microwave background feedhorn arrays that can be used to produce beam maps, measure beam performance, and evaluate the horns compatibility to the Si wafer detector at sub K temperatures, and explore Phase III transition to either ACTPol or the Simon’s Observatory. Commercial applications for the combined additive manufacturing and electrochemical surface finishing processes include components that require fine structures and are difficult to finish using conventional techniques. Uses in the Department of Energy including fossil and green energy, accelerator development, and quantum information system sectors.