1. CM-26 Cooler and Lead Test1 Tests of a PT415 Cooler with HTS Leads in the Drop-in Mode Michael A. Green Lawrence Berkeley Laboratory, Berkeley CA 94720, USA

2. CM-26 Cooler and Lead Test2 The Purpose of Cooler and Lead Test The cooler performance was to be measured as a function of the first stage heat load and the second stage heat load. Re-condensation was tested. Without re-condensation there is no cooling of the MICE magnets. The heat leak down the copper leads was measured at zero current and at 275 A. The lead performance was measured for two different lead IL/A’s. The temperature drops across the cooler drop-in joint, the intercepts for heat the room temperature leads and the copper between the leads and the cooler were measured. The test provided a measurement of the system time constant as a response to changes.

3. CM-26 Cooler and Lead Test3 First PT-415 Drop-in Cooler Test Photos 1st Stage heater and Tapered Plate 2nd Stage heater and Condenser PT-415 Drop-in Cooler

4. CM-26 Cooler and Lead Test4 Schematic Diagram of the Lead Test

5. CM-26 Cooler and Lead Test5 Lead Test Assembly Photos

6. CM-26 Cooler and Lead Test6 Photos of the Lead Test with a PT415 Cooler

7. CM-26 Cooler and Lead Test7 The saturation temperature of the helium in the tank can be determined by the tank pressure. The temperature sensor on the tank is not very accurate so the tank sensor was calibrated using the temperature calculated from the tank pressure. T = 2.1978 + 4.0759 P-3.5897 P 2 + 1.9306 P 3 -0.41073 P 4 T is given in K. P is given in bar Helium Temperature is determined by Pressure

8. CM-26 Cooler and Lead Test8 Calibration of the Tank Temperature Sensor

9. CM-26 Cooler and Lead Test9 Cooler Performance with Two IL/A Leads Not in Equilibrium

10. CM-26 Cooler and Lead Test10 Tests of 4 Identical Leads, an Example of the Test not being in Equilibrium For T 2, the time to come equilibrium is ~10 hours. For T 1, the time to come equilibrium is ~1.5 hours.

11. CM-26 Cooler and Lead Test11 Observations Concerning the Cooler Tests The copper leads used in the previous magnet 2 had a heat leak that was too high. The IL/A for these leads was 5.3x10 6 A m -1. Is was clear that this IL/A was too large. The second leads tested had an IL/A = 3.1x10 6 A m -1. The ICST calculations for IL/A suggest that the copper lead IL/A should be 3x10 6 A m -1 for copper leads with an RRR = 10. The RRR of the cable used for the leads was unknown. IL/A is an important design feature for the leads. It appears that an IL/A of 3 x 10 6 A m -1 is about right. The time to come to equilibrium (four time constants) is long for the experiment (~10 hrs). The magnet equilibrium time constant is proportional to the helium mass and inversely proportional to the number of coolers and the cooling power per cooler at 4.2 K.

12. CM-26 Cooler and Lead Test12 Cooler Test Observations continued From the operating diagram it is clear that the cooler first stage temperature should not be greater than 45 K. This means that the first stage heat load should be less than 50 W. The HTS lead lead current is limited by temperature and magnetic field. The temperature drop between the top of the HTS leads and the cooler first stage is very important. The  T in the drop-in joint was 1 to 2 K. The  T from the leads to the copper plate was about 1 K. In the experiment, the copper plate that carried heat from the lead heat intercept to the cooler had the largest  T. The copper plates for all of the MICE magnets should be thicker and the distance from the leads to the coolers must be minimized.