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Splice Joint Design and Analysis John Escallier Brookhaven National Lab

US LHC Accelerator Research Program. bnl - fnal- lbnl - slac. Splice Joint Design and Analysis John Escallier Brookhaven National Lab. Splice Joint Design overview (1). Impregnated coil structures have compromised heat paths Epoxy has limited thermal conductivity

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Splice Joint Design and Analysis John Escallier Brookhaven National Lab

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  1. US LHC Accelerator Research Program bnl - fnal- lbnl - slac Splice Joint Design and AnalysisJohn EscallierBrookhaven National Lab

  2. Splice Joint Design overview (1) • Impregnated coil structures have compromised heat paths • Epoxy has limited thermal conductivity • Conductor to epoxy bonds are less thermally conductive than the epoxy or the metals • TCE mismatches fracture epoxy to metal bonds • Splice joints generate heat from IR loss • Splice design affects generated heat • Total overlap area • Solder thickness • Joint topology

  3. Splice Joint Design overview(2) • Splice design affects heat removal to helium • Total length and cross sectional area of the NbTi leads within the impregnated structure • Current sharing details • Splice topology • Lead topology and stabilization

  4. Full heat flux pathway Niobium Titanium (orange) Solder (green) Dissipation source Spread to turns Peak source temperature Niobium3 Tin (maroon) Heat to helium Spread to adjacent coil Heat to coils

  5. Steady state condition

  6. Splice joint temperature profile at 11 kAmps • Assumptions: • 11 Kiloamp current (input variable) • Joint resistances of 1 nano-ohm (input variable) • Uniform joint cross section • NbTi cable effective thermal conductivity 70% room temperature copper (input variable) • No thermal path provided by epoxy • Liquid helium temperature of 4.5 kelvin (input variable) • Linear material properties in the 4 to 10K range (equations may be used)

  7. Impact of effective joint resistance on final temperature at 11 kAmps

  8. Overview of possible splice geometries

  9. Interconnect type A (5.3 Kelvin if the leads are soldered together their length) Soldering the two leads will current share and reduce dissipation by 20 percent

  10. Interconnect type B 5.3 Kelvin final temperature

  11. Interconnect type C 4.9 Kelvin final temperature

  12. Splice Joint Summary • Vacuum impregnation: • removes direct helium contact cooling of all conductors and connections • creates higher temperatures internally given internal dissipations • Splice design requires configuring conductor layers in the splice for reduced dissipation • Splice design needs to provide adequate thermal conductive paths to helium for generated heat • I squared R dissipated heat

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