A High-Emissivity Coating Design for the Mu2e Target

The Mu2e production target generates pions that decay to muons when it is bombarded by a high energy high power primary proton beam. The target was initially designed with a consideration of 8 kW incident power by the deposited proton beam, and adopted the configuration of using a compact target geometry that minimizes pion re-absorption and using the refractory metal: Tungsten. However, in a recent study, Mu2e-II would prefer a beam energy between 1 and 3 GeV and a higher incident proton beam power at 100 kW, benefiting from the improvements from PIP-II. This new requirement raises the absorbed power in the target from 760 W to about 10 kW, which immediately renders the current radiation cooling inadequate for continuous troubleless operations. Euclid Techlabs, LLC proposes to develop a problem-solving coating design for the Mu2e radiation cooled production target. The proposed coating studies include research on the coating material and surface treatment. The new coated target has a great potential to significantly increase the target lifetime and tolerance against high power deposition rate in Mu2e-II. We will collaborate with Fermilab (contact: David Pushka) to set up emissivity tests for our coated coupons and evaluate the thermal and stress properties of the target using newly measured data. In Phase I, we will use our Geant4/MARS expertise to evaluate the pion productivity with the coating, then process the coupons for tests at Fermilab. ANSYS simulations will be done to assess temperature and stress distributions in the target using the new data and finite element analysis. The above process will be repeated to optimize the recipes until the end of Phase I. The best coating treatment will be proposed for full target coating and tests in Phase II. The Mu2e experiment will be upgraded to the next generation with more beam power soon. The collaboration will have a more reliable, continuous beam time with a robust target, while not changing the target station design. This saves huge effort for Fermilab and HEP physicist to redo the physics analysis setup, keep a well- defined history of changes in the simulation software, such as the way it was done for MICE using Markdown Languages or ROOT, which did cause complications to reconstruct data. Other HEP experiments, especially those in the design stage, will consider to use similar coating on their targets to reduce or even avoid water or even helium cooling.