Cooldown data: Cernox thermometers on a niobium plate 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 Manganin 32 AWG 4 K heater 4 K stage (OFHC) Indium foil Adapter block (5N Al) Niobium plate Cernoxes 2 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Setup details • 17 calibrated Cernox thermometers (CU package) - 3 x 3 array, 0.6” x 0.6” spacing - 9 sensors on top face, 8 on the bottom - 4-40 screws finger-tight - augmented with Apeizon N grease • Niobium plate - 2 inches wide x 2.8 mm thick - 8.5 inches long • Plate wrapped with 10 layers of MLI 3 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Cooldown Vacuum start Cooler start Shield ≈ 59 K Heating cycles Nb plate (17 Cernoxes) ≈ 3.4 - 3.5 K 4 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Cooldown around 9 K No noticeable change in the cooldown rate around NC-SC transition 5 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Spread near base temperature Thermometers T1 - T9 on the face touching the cooler Thermometer layout on the Nb plate Thermometers T10 - T17 on the back face 0.6” x 0.6” array T1 Row 1 1, 10 4, 13 7, 15 T16 2, 11 5, - 8, 16 Row 2 Row 3 3, 12 6, 14 9, 17 Heat flow path • Thermometers from the same row bunch up; spread ≈ 25 mK (similar to with the copper plate); T1 and T16 are outliers of their bunches • A heat flow appears along the plate towards the cooler with Row 1 being the warmest and Row 3 the coldest. 6 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Heat flow rate estimation 0.6” x 0.6” array Along the Nb plate... Row 1 1, 10 4, 13 7, 15 L = 1.2”, dT = 60 mK q Nb ≈ 14 mW with k Nb = 50 W/m-K 5, - 8, 16 2, 11 Row 2 9, 17 Row 3 3, 12 6, 14 If our copper plate was seeing the Heat flow path s ame heat flow… Δ𝑈 𝐷𝑣 ≈ 2 mK (<< 40 mK spread) 2.8 mm 2” 7 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Heating cycles NC SC No noticeable change during warm up or cooldown 8 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Summary • Outliers exist but majority of the Cernox thermometers (15 of 17) show spread similar to when they were on the copper plate • All 17 thermometers pass smoothly through NC-SC transition temperature of niobium • There does not appear a fundamental limitation that would limit the Cernox CU package from measuring SC niobium temperature 9 Dhuley, Geelhoed | Calibration cooldown 6/7/2017
Recommend
More recommend
