Experimental study on heat transfer through a few layers of multilayer insulation from 300 K to 4.2 K Zhanguo Zong, Norihito Ohuchi, Kiyosumi Tsuchiya, Yasushi Arimoto and Hiroshi Yamaoka Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki, , Japan

(Thu.)2 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Content Research background −SuperKEKB project at KEK −The final focusing SC magnet system of the SuperKEKB, design, construction and status Measurement system set up −Vertical cryostat with doubled LHe vessels −Warm bore, inserted in LHe −Calorimeter of thermal conduction −Modified LHe boil-off methods Measurement results and discussion

(Thu.)3 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India SuperKEKB project at KEK Situated in Tsukuba −60 km from Tokyo Accelerator/detector −Linac −Main ring (~3 km) −Experimental hall for detector Link to information −

(Thu.)4 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India SuperKEKB project at KEK The accelerator on the "luminosity frontier” −40 times higher to KEKB −Linac upgrade −Reinforcing RF systems −New damping ring for positron beam −Replacing beam pipes. −Nano-beam scheme (50 nm) by the final focusing SC magnets at the interaction region Cited from Y. Funakoshi, Lecture for Sakura Science Plan, Introduction to Accelerators for Students, July 7th KEK

(Thu.)5 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Status of the SuperKEKB project Trial operation (Phase I commissioning, without final focusing SC magnets and detector) −Link to information: Link to information −

(Thu.)6 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Final focusing SC magnet system of the SuperKEKB The key components to achieve the target – final focusing before colliding, under the stringent space constraints: outer size – limited by the detector and inner size – by beam pipe

(Thu.)7 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Final focusing SC magnets of the SuperKEKB Quadrupole doublets for each beam: 8 main SC quarupoles To exclude the effect of solenoid field by the Belle-II detector: 4 compensation solenoids To correct the misalignment of the main quadrupole coils: 43 corrector coils The SC magnets are assembled into two cryostats, at the left and right sides of the detector, cooled by sub-cooled LHe at 1.6 bar and 4.5 K

(Thu.)8 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Status of the final focusing SC magnets All the SC coils were fabricated and measured in the LHe, vertically. QCSL was delivered to our lab by the end of last year. QCS-R is by the end of this year

(Thu.)9 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Cooling the SuperKEKB QCSL cryostat Cooling QCS-L cryostat at our lab −To energize all the SC magnets with operation currents. (4 main, 1 solenoid and 20 SC correctors) −Horizontal field measurement (about 3 months) −LN2: 900 L/day for 24 hours cooling 80 K thermal shields. −LHe: 1000 L/day for 3 hours cool down (from 50 K to 4.2 K) and 6 hours for field measurements.

(Thu.)10 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India SC corrector coils of the final focusing SC magnets The radial spaces for the SC corrector coils are between the LHe vessel tubes and the inner windings of the main quadrupole coils. SC correction coils: 20 coils for the left and 23 coils for the right, fabricated with BNL Direct Wind techniques.

(Thu.)11 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Heat transfer through the gap and multilayer insulation ItemQC1PQC1EQC2PQC2E Outer radius of beam pipe Inner radius of coil bobbin Gap for MLI Heat transfer through the gap −LN2 shield are not applied. −To elevate the operation temperature. −To increase heat loads of the cryostats. MLI (the so-called superinsulation) −The best performance of all thermal insulation −The actual performance depends on a few parameters hard to control. −No data available for a few layers (<10 layers) Extensive studies and experimental measurements are necessary to evaluate the thermal performance of MLI and to obtain application experiences and fabrication details in the specific circumstances.

(Thu.)12 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Set-up of measurement system Vertical cryostat and warm bore with an evacuated gap to accommodate variable MLI layers Calorimeter of thermal conduction (G10 wall)

(Thu.)13 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India G10 with the temperature sensors Sensors with thermal grease (Apiezon N cryogenics) Temperatures with deviations −Thermal bridge due to MLI touch −Local conditions of thermal transfer Set-up of measurement system

(Thu.)14 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Modified LHe boil-off method Doubled LHe vessels to intercept the heat leaks down the cryostat wall −Keep the outer LHe level higher than the inner The thermal radiation heat leaks adsorbed by the LHe, is proportional to the length in the LHe. −By measuring the LHe level (L LHe ) and helium vapor flow rates (m).

(Thu.)15 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Modified LHe boil-off method Linear relation between the evaporated helium vapor and the LHe levels after LHe transferring (From 65% to 30%) o kg/m 3 kJ/kg −Slope: heat leak per unit length Modified helium boil-off method −Fitting slope −LHe boil-off method

(Thu.)16 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Set-up of measurement system Fitting constant −Due to thermal conduction of the SUS support plate −Ansys TM model (0.12 W/0.13W)

(Thu.)17 Zhanguo ZONG, ICEC26-ICMC2016 | Manekshaw Centre, New Delhi, India Measurement results Conclusion for final focusing SC mangets −When MLI is less than 5 layers, heat flux has a fast reduction with increasing MLI layers. The heat flux density are less than 5 W/m 2 (L>5) −Temperature differences, ∆T, as a reference to the LHe boil-off method −The total area, 0.86 m2, have a total heat leak of 4.3 W due to thermal radiation. −The temperatures of SC cables of SC corrector coils are elevated less than 0.2 K. −Sub-cooling LHe (0.5 Watt / g/s, ∆T= 0.1K)

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