Al-Al contact resistance: First results with the two-heater one- thermometer method Ram Dhuley, Michael Geelhoed Cryocooled-SRF group meeting 7 June 2017
Schematic of the test setup PT Reg. 60 K stage (OFHC) ETP copper 22 AWG 4 K heater Al-Al contacts 4 K stage (OFHC) Indium foil Adapter block (5N Al) Copper Tree 2 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Two-heater one-thermometer (2H-1T) method To cryocooler Downstream heater, H D Thermometer, T D is optional Q Thermometer, T U Method schematic Al plates Upstream heater, H U Step 1: Q HU = Q in , Q HD = 0, T T T measure T U = T 1 Result U 1 2 R Procedure c Q Q in in Step 2: Q HU = 0, Q HD = Q in , (R c = contact thermal resistance) measure T U = T 2 3 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Test assembly 2 x Al-Al contacts 4 K head Copper tree 2 x Al-Al contacts 4 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Details of Al-Al contacts Copper tree connects here Joints J1 and J2 Joints J3 and J4 (distorted while tightening, one heater failed; no measurements were made) 5 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Details of joints J3 and J4 Joint assembly (Oleg’s recipe) - 1” x 1” contact - 5/16-18 screw (steel) tightened to 75 in-lbf TU - 5 mil indium interposer HD Heaters TD HU HU - Minco kapton film (37 ohm) - Glued with GE-Varnish - Taped around with copper adhesive tape TU This being the first run with the Thermometers HU 2H-1T method, we used a - Cernox CU packages thermometer downstream for - Interposed with Apeizon N grease sanity check - Finger tightened with 4-40 brass screws 6 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Results: Temperature data 𝛦𝑈 𝑉 -Joint 3 𝛦𝑈 𝑉 -Joint 4 Base T, offsets H U -Joint 3 ON, H D ON, H U -Joint 4 ON, Rest OFF Rest OFF Rest OFF All heaters OFF 7 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Results: Thermal resistance • This test: Al-Al contact resistance = 0.68 - 0.73 K/W @ 4 K • Oleg’s test (Run 10): Al -Al contact resistance = 0.55 K/W @ 4 K 8 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
Next… Develop recipe to make Al-Nb contacts - without distortion - with known tightening force - using SRF compatible materials - taking into account differential thermal contraction of Al, Nb, bolt material Distorted joint Measurements with the copper tree 9 Dhuley, Geelhoed | Al-Al contact resistance 6/7/2017
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