1. WUT Experience in Measurements of the Heat Transfer Thought SC Cable Electrical Insulation Jaroslaw Polinski*, Maciej Chorowski*, Michal Strychalski*, Rob van Weelderen** Mini-Workshop on Thermal Modeling and Thermal Experiments for Accelerator Magnets – CERN 30th Sep – 1st Oct 2009 * Wroclaw University of Technology, Poland ** CERN, Switzerland

2. Outline Motivation of the heat transfer program at WUT (new HT method) Experimental set-up at WUT Sample holder design Sample compression idea Insulation schemes and sample preparation Test results Conclusions

3. Motivation of the heat transfer program at WUT „Stack of the conductors” – the most common measurement method of the heat transfer through S.C. cable electrical insulation CERN stack holderKAK and CEA Saclay stack holder

4. Motivation of the heat transfer program at WUT Stack methodNew method Heater T sensor

5. Method comparison Stack method Advantages –The most similar with real magnet coil configuration Disadvantages –the amount of the heat transferred through insulation by particular HT path is difficult to determinate New method Advantages –allows determination of the heat transfer resistance of the insulation and the Rutherford type cable Disadvantages –cable sample configuration is „far” from magnet coil configuration

6. Superfluid helium cryostat designs Scheme of pressurized superfluid helium cryostat

7. Superfluid helium cryostat designs Radiation screen with MLI Measurement vessel with instrumentation External vacuum jacet during leak test

8. HeII cryostat set-up in WUT He II Cryostat He I dewar pressurization system He IIs vessel pressure control valve High capacity vacuum pump

9. Holder designs Cable sample T sensor Heater Holder body Capillary Compressive lid Compressive element Sealing substance Sample seat Bolts

10. Holder designs Holder body

11. Holder designs Cable sample seat

12. Holder designs Cable sample seat with sample and compressing element on the top

13. Holder designs Holder installed in the cryostat (left) and covered by measurement vessel (right)

14. Sample compression idea Except bolts, all holder elements are made of Invar Bolts are made of stainless steal Compression applied on the sample: N b – number of bolts A b – bolt rod cross section area, m 2  SS – thermal expension of stainless steal, m/m  Inv – thermal expension of invar, m/m E SS – Young modulus of stainless steal, Pa A samp – cable sample surfacae, m 2

15. Sample compression idea For: 6xM12 bolts with rod cross section area A b =80mm 2 Thermal expansion of Invar (300–2K) -  =0.00038 Thermal expansion of SS (300–2K) -  =0.0031 Young moduls of SS: E SS =2.1. 10 9 Pa Sample surface: A samp =98×16 mm × mm The compression applied on the sample p=160MPa But Mechanical deformation of the cable sample is assumed to be as for Invar material Due to complex cable structure its precise mechanical deformation is theoretically very difficult to determinate

16. Sample compression idea Therefore: Additional mechanical tests have to be performed where sample compression values vs. room temperature pre-compression will be determined The mechanical tests preparation is already started The test will be performed in LN2 and results scaled to He temperature

17. Insulation schemes Dipole type Quadruple type Enhance type A Enhance type B

18. Cable sample preparation and installation

22. Tests description Test No Insulation type Side A/B Sample sealing substance Sample seat sealing (Apiezon) Compressing element Capillary 1D/APiceineNo OPEN 2D/DPiceineNo OPEN 3A/AEpoxy resine1YesNoOPEN 4Q/QEpoxy resine2Yes OPEN 5B/B 3M Scotch Weld DP 150 Yes CLOSE

23. Reference data B. Baudouy a,*, M.X. Francßois b, F.-P. Juster a, C. Meuris: „He II heat transfer through SC cables electrical insulation” - Cryogenics 40 (2000) 127-136 First layer: Kapton 150 HN (37.5 mm), 50% overlap, 11-mm width Second layer: Adhesive Kapton 120 (30 mm), 4 mm spacing Drum method

24. Test results Test no.1 Sealing substance – Piceine T bath =1.8K

25. Test results Test No 1 conclusions Observations: –Obtained results are of 2 orders of magnitude higher than „Reference Results” –After samples dismounting a visual inspection shows that piceine don’t fill the space between insulation and cable sample seat very well Correction to be done –Piceine sealing substance should be applied more precisely

26. Test results Test no.2 Sealing substance – Piceine T bath =1.8K

27. Test results Test No 2 conclusions Observations: –Obtained results are still 2 order of magnitude higher than „Reference Results” –After samples dismounting a visual inspection shows that piceine don’t fill the space between insulation and cable sample seat very well Correction to be done –Piceine sealing substance should be substitute with some epoxy resin –Sealing between sample seat and the holder body should be created. To allow disassemble of the sample seat from the holder body after test an Apiezon vacuum grease have been chosen

28. Test results Test no.3 Sealing substance – Epoxy 1 Sample seat sealing - YES T bath =1.8K

29. Test results Test No 3 conclusions Observations: Story of Some Compressing Elements Michal: The cryostat is ready. We can start the test. Jarek: Great!!! By the way: what is that? Michal: This is one of the compressing element from the holder. Jarek:.....?.....?....? Michal: What? Jarek: Why the these elements aren’t installed in holder? Michal: Because if you install them after the holder is not fit to the measurement vessel. It is 1 or 2 mm too width Jarek:.....?.....?....? Michal: These elements are important? Jarek: Quite

30. Test results Test No 3 conclusions Observations: –Lack of the compressing elements in the holder for test No:1, 2 and 3 –Obtained results are „only” 1 order of magnitude higher than „Reference Results” –After samples dismounting a visual inspection shows air bubbles in sealing epoxy resin –In test No 1, 2 and 3 the „Lambda transition” occur at T=1.85K what corresponding to p HeIIp =20mbar

31. Test results Test No 3 conclusions Correction to be done –Reducing of the compression elements to high allows the holder installation in the measurement vessel –Test the other type of the epoxy resin –Solve the problem of „low temperature lambda transition”

32. Test results Solve the problem of „low temperature lambda transition”

33. Test results HeI bath HeIIp bath HeIIs bath Solve the problem of „low temperature lambda transition” Lambda valve JT valve

34. Test results Test no.4 Sealing substance – Epoxy 2 Sample seat sealing - YES Compressing element – YES T bath =1.8K

35. Test results Test No 4 conclusions Observations: –Obtained results are already in this same order of magnitude as „Reference Results”, but „Reference Results” are for uncompressed insulation since our sample is compressed. –„Lambda transition” occur at  T=0.45K i.e. T=2.25K –After samples dismounting a visual inspection shows no air bubbles in new sealing epoxy resin

36. Test results Test No 4 conclusions Correction to be done –heat transfer thought capillary should be experimentally determined –T sensors should be re-calibrated in pressure controlled superfluid saturated helium –sealing of the capillary should be considered

37. Capillary sealing Capillary scheme Capillary sealing

38. Test results Test no.5 Sealing substance – 3M Scotch Weld DP 150 Sample seat sealing - YES Compressing element – YES Capillary - CLOSE T bath =1.8K

39. Test results Test No 5 conclusions Observations: –Obtained results seems to be already correct. –„Lambda transition” occur at different temperature for each side and for both case it not correspond to T-lambda temperature possible reason: after reviewing of the temperature data recorded during the test it was found that connection of the heater wires to power supply results in change in temperature reading values. Since temperature regulation in measurement bath is based on one of T-sensor reading value after power supply connection a real temperature in HeIIp bath was different. Correction to be done - Rewinding the instrumentation wires or grounded the cryostat and/or acquisition system

40. Conclusion Numbers of problems concerned the heat transfer test have been solved To start the new tests series with electrical insulations mechanically wrapped on the cables a following actions have to be taken: –determination of the final („cold”) sample compression values in function of the pre-compression in room temperature –instrumentation reading problem have to be solved