Preliminary Engineering Report nEDM Central Detector

1. Preliminary Engineering ReportnEDM Central Detector John C. Ramsey Los Alamos National Laboratory nEDM Collaboration Meeting ASU 2/2008

2. Objectives • Sound out assumptions • Materials choices • Design rationale • Component placement • Interfaces with other subsystems • Voice concerns • See list above! • Obtain feedback and initiate communications nEDM Collaboration Meeting ASU 2/2008

3. Major assembly assumptions • What is here is in no way set in stone! • Assembly cantilevered off of central volume composite end plate • Material of choice wherever possible is acrylic (PMMA) to minimize thermal contraction mismatches • We are able to coat the acrylic for the electrodes and return • No metal components closer than 1 meter upstream of the end plate • Light guides not currently included in the model nEDM Collaboration Meeting ASU 2/2008

4. Central volume cap • Mounting plate for entire cantilevered assembly • Feedthroughs for light-guides, services, etc. • Assumptions • G-10 is superfluid tight provided low enough stress levels • 1.5” thick G-10 with carbon fiber reinforcing plate • Windows are large enough to compensate for thermal contraction • We can seal G-10 cap to G-10 vessel • We can seal the feed-throughs nEDM Collaboration Meeting ASU 2/2008

5. Acrylic interface plate • Large contraction mismatch between acrylic and G-10 • Radial slots keep back plate concentric as acrylic contracts • Supports entire cantilevered assembly • Studs and Belleville washers may replaced with PTFE glides nEDM Collaboration Meeting ASU 2/2008

6. HV return and support • Provide structural support to all components • Additional support tube handles axial loads from the capacitor • HV return is coated (striped?) for conductivity nEDM Collaboration Meeting ASU 2/2008

7. Electrode assemblies • Hollowed acrylic • Coated for conductivity • Acrylic supports to HV return • Hidden from E-field • One or more coated to provide HV return path? nEDM Collaboration Meeting ASU 2/2008

8. Light guide and cell assemblies • Level of detail currently low • Assuming glued box for the cells • Can we make a well performing, separable mechanical joint for the light-guide/cell interface? • Light-guides need support at multiple locations nEDM Collaboration Meeting ASU 2/2008

9. 3He service to the measurement cells • 2” OD, 1.5” ID acrylic piping (per George’s current assumptions) • Bellows to allow for system contraction • Bell crank actuated V1 valve nEDM Collaboration Meeting ASU 2/2008

10. SQUIDs • Silicon substrate resting on acrylic pads • Located with a pair of pins on the V1 valve housing (not shown) • Placement along cell centerline makes V1 valve packaging very difficult and compromises the cell opening • Splitting up the SQUID array? nEDM Collaboration Meeting ASU 2/2008

11. V1 Valve • Torlon return spring – to be tested • Rod or rope actuation of bell crank • Larger area housing body • 0.75” cell penetration • Very tight requirements for cell wall surface quality with valve closed • Acrylic is very brittle…vespel? d-vespel? • Flushing pipes with V1 valve closed? nEDM Collaboration Meeting ASU 2/2008

12. Current and future efforts • FEM models • Simple 2” disc transient thermal model • to examine stresses induced by cool down rate • Full assembly • Gravity, other structural loads • Thermal contraction • Cooldown simulation • G-10 seal test vessel • Continue iterations and development in coordination with the various relevant subsystems nEDM Collaboration Meeting ASU 2/2008