FPC Thermalisation Update Niklas Templeton 16/6/16

FPC Thermalisation Analysis Aim: To validate new FPC thermalisation model – 8 x small straps To compare thermal contact solutions, i.e.: –Fastened SS-Cu –Fastened Cu-Cu (coated FPC interface) –Fastened SS-In-Cu (Indium buffer) To compare thermal strap geometries: –25 x 3 mm –30 x 3.5 mm –30 x 5 mm Solving to minimise 2K Heat Load –FPC Budget: 9.6 W (4.8 W per FPC) 1

New Model 253 mm 83 mm 170 mm Intercept height as agreed based on empirical calculations Thermalisation is close to RT interface while strap connection remains feasible dT = ≈ 225 K, L ≈ 51 mm 8 x thermal braided straps, L ≈ 90 mm dT 2

FPC Dynamic Heat Load Dissipated power density ANSYS heat flux imported from HFSS Conservative Load >2x expected Less conservative RF Dynamic Heat Load calculated as 5 W per FPC using ANSYS HFFS Interpolated Heat Flux to be applied on FPC can inner wall Area (m 2 ) Case 1Case 2 Flux (W/m 2 )Heat Load (W)Flux (W/m 2 )Heat Load (W) A9.71E B7.77E C4.86E D3.88E E4.86E F5.83E G3.88E H7.14E A B A C D F G H E RF dynamic heat loads have been interpolated from previous simulations to give a realistic heating profile to FPC inner wall. Heat loads are approximate but should be sufficiently accurate for strap design validation and optimisation. 3

Steady State Thermal Analysis Engineering Data FCP Can: SS 316 Thermal Strap: Cu ETP Boundary Conditions 295 Bellows connection 70 Thermal Shield Connection (close to worse case) 2 Cavity connection Interpolated heat flux (see image) Assumptions & Limitations Neglecting radiation Neglecting shield connection & pipe convection Previous studies show an increase of 10-20% in 2K heat leak with thermal shield Thermal Conductivity Data 4

Initial Results 8 straps, 25 x 3 mm - equiv. section 40 mm 2 Total Cross Section: 320 mm 2 FPC-Strap Connection: SS-Cu Fastened TCC: 150 W/m 2.K (Nominal) Comment: dT is acceptable (~10 K) 2 K Heat Load is too high Greater TCC and/or Strap Section required *RF Heat load may be overly conservative Repeating analysis with 5.6 W dynamic heat load gives: Reaction Results (W) 2 K70 K295 KRF Reaction Results (W) 2 K70 K295 KRF dT Result Verification Q = K.(A/L).dTQ (W):25.34dT (K):12.96 (W.m.K):~550√ dT = Q.L / K.AA (m2): l (m): RESULTS ARE NOT CONCLUSIVE – BASED ON POOR TCC & INITIAL STRAP GEOMETRY

Ref: Thermal Contact Conductance Data 6

8 straps, 25 x 3 mm - equiv. section 40 mm 2 Total Cross Section: 320 mm 2 Comment: Given strap geometry requires extremely good contact connection (i.e. brazing) which may not be achievable *RF Heat load may be overly conservative Repeating analysis with 5.6 W dynamic heat load gives: Repeated Analysis suggests requirements can be met with good fastened connection Thermal Contact Conductance Connection Comparison TCC (W/m 2.K) 100Fastened SS-Cu (poor contact) 300Fastened SS-CU (v. good contact) 500Fastened Cu-Cu (coated FPC interface) 1000Fastened with indium buffer SS-In-Cu IdealPerfectly bonded connection *Brazed Strap would perform between 1000 and ideal – feasibility to be checked as it may damage strap Reaction Results (W) 2 K70 K295 KRF TCC (W/m 2.K) Ideal Conservative Reaction Results (W) 2 K70 K295 KRF TCC (W/m 2.K) Ideal Realistic 7 2K Heat Load Specification of <4W has been used for the analysis (4.8W with 20% contingency)

In order to achieve less than 4W heat leak to 2K, a TCC of at least 180 or 600 W/m 2.K is required, depending on selected heat load model. Suggestion is to keep the TCC conservative and Heat Load less conservative (5.6 W) as not to ‘overkill’ the analysis. 8

8 straps, 25 x 3 mm - equiv. section 40 mm 2 - Total Cross Section: 320 mm 2 8 straps, 30 x 3.5 mm - equiv. section 50 mm 2 - Total Cross Section: 400 mm 2 (25% increase) 8 straps, 30 x 5 mm - equiv. section 75 mm 2 - Total Cross Section: 600 mm 2 (88% increase) Next available geometry: 40 x 6 mm - equiv. section 120 mm 2 but is more difficult to integrate with FPC connection… Results – Strap Comparison Reaction Results (W) 2 K70 K295 KRF2 K70 K295 KRF TCC (W/m 2.K) TCC (W/m 2.K) Reaction Results (W) 2 K70 K295 KRF2 K70 K295 KRF TCC (W/m 2.K) TCC (W/m 2.K) Reaction Results (W) 2 K70 K295 KRF2 K70 K295 KRF TCC (W/m 2.K) TCC (W/m 2.K)

Increasing the strap section improves thermalisation performance although increase is non-linear. It is advisable to use the largest possible section compatible for integration but equal, if not greater, importance should be placed on contact quality. Contact quality depends on Surface Roughness, Flatness, Contact Pressure, Material Conductivity. 10

Conclusions Using several smaller thermal straps, as opposed to 2-3 large straps, is a viable solution. Intercept height gives low heat load at 2K, with higher thermal shield load and will require heaters at the FPC. As expected, greater Contact Conductance & Strap Section improves performance 30 x 5 mm straps with good fastened contact should results in less than 4W heat 2 K, per FPC, without the need for specialist connection. To be analysed with thermal shield and pipe convection alongside long strap - fewer contact resistance option… Alternative thermal path option 11