US LHC Accelerator Research Program bnl fnal lbnl

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US LHC Accelerator Research Program bnl - fnal- lbnl - slac Splice Joint Design

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 •

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 2

Splice Joint Design overview(2) • Splice design affects heat removal to helium • Total

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

Full heat flux pathway Spread to turns Peak source Niobium 3 Tin temperature (maroon)

Full heat flux pathway Spread to turns Peak source Niobium 3 Tin temperature (maroon) Niobium Titanium Solder Dissipation (orange) source (green) Heat to helium Spread to adjacent coil Heat to coils 4

Steady state condition 5

Steady state condition 5

Splice joint temperature profile at 11 k. Amps Conductor temperature vs distance into the

Splice joint temperature profile at 11 k. Amps Conductor temperature vs distance into the joint Assumptions: 11 Kiloamp current (input variable) 5. 2 Joint resistances of 1 nano-ohm (input variable) Uniform joint cross section 5 Nb. Ti cable effective thermal conductivity 70% room temperature copper (input 4. 8 variable) No thermal path provided by epoxy temp 4. 6 Liquid helium temperature of 4. 5 kelvin (input variable) 4. 4 Linear material properties in the 4 to 10 K range (equations may be used) Temperature Kelvin 5. 4 4. 2 4 0 1 2 3 4 5 Inches into the solder joint 6 7 6

Impact of effective joint resistance on final temperature at 11 k. Amps Peak temperature

Impact of effective joint resistance on final temperature at 11 k. Amps Peak temperature in Kelvin 9 Internal splice temperature peak based on 4. 5 K station 8 7 6 5 4 peak temp 3 2 1 0 0 1 2 3 4 5 6 Joint resistance, nano-ohms 7

Overview of possible splice geometries 8

Overview of possible splice geometries 8

Interconnect type A (5. 3 Kelvin if the leads are soldered together their length)

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 9

Interconnect type B Peak temperature in Kelvin 9 Internal splice temperature peak based on

Interconnect type B Peak temperature in Kelvin 9 Internal splice temperature peak based on 4. 5 K station 8 7 6 5. 3 Kelvin final temperature 5 4 peak temp 3 2 1 0 0 1 2 3 4 5 6 Joint resistance, nano-ohms 10

Interconnect type C Peak temperature in Kelvin 9 Internal splice temperature peak based on

Interconnect type C Peak temperature in Kelvin 9 Internal splice temperature peak based on 4. 5 K station 8 7 6 4. 9 Kelvin final temperature 5 4 peak temp 3 2 1 0 0 1 2 3 4 5 6 Joint resistance, nano-ohms 11

Splice Joint Summary • Vacuum impregnation: • removes direct helium contact cooling of all

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 12