Stress Analysis of the nEDM Central Volume Container

Abstract

This thesis entails the design progression and finite element analysis (FEA) of one component in a complex system designed to conduct an experiment that improves the measurement technique and accuracy of the neutron electric dipole moment (nEDM). Numerous organizations have been in collaboration on this project since 2002.

In detail, the component being analyzed is the helium insulation volume or central volume container. The central volume is a pressurized cylindrical container designed to operate at an internal pressure of approximately 1.5 atmospheres and a temperature range of 0.30 - 0.45 Kelvin. Liquid Helium (LHe) will be used as the cooling medium for the experiment. It is vital that the container be constructed exclusively from a non-magnetic, non-metallic, and non-conducting material that is not activated by neutrons. The Eddy current and magnetic fields surrounding the experimental apparatus would be disrupted with the use of metallic components producing invalid experimental results.

As the design of the central volume progressed, numerous finite element analyses were completed with ANSYS. The design recommendations and an outline of the design progression are detailed in the following document. From the FEA analyses completed on the central volume container, it was concluded that a material combination using G10-CR for the downstream end flange, light-guide feed-through collars, and upstream flange, S2/5216 for the cylinder, retaining rings, and support strips, and sapphire for the light-guide windows produced the most favorable stress results. The design of the upstream flange assembly has not been finalized; therefore, the stress values obtained in this area with the FEA are high and inaccurate.

The margin of safety (MOS) was calculated using allowable stress equations provided by the safety engineers with Oak Ridge National Laboratories. A MOS value greater than 0 is considered a favorable result. The resulting MOS values for the material combination listed above ranged from -0.40 to 1.57. The results were also tabulated for the maximum principal strains for each component of the central volume container. The resulting MOS values based on the allowable strain values for the same material combination mentioned above ranged from 0.38 to 2.44.