Tests of a PT415 Cooler with HTS Leads in the Drop-in Mode

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

2. 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. CM-26 Cooler and Lead Test

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

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

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

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

7. Helium Temperature is determined by Pressure 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 P2 + 1.9306 P3 -0.41073 P4 T is given in K. P is given in bar CM-26 Cooler and Lead Test

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

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

10. Tests of 4 Identical Leads, an Example of the Test not being in Equilibrium For T2, the time to come equilibrium is ~10 hours. For T1, the time to come equilibrium is ~1.5 hours. CM-26 Cooler and Lead Test

11. 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 5.3x106 A m-1. Is was clear that this IL/A was too large. The second leads tested had an IL/A = 3.1x106 A m-1. • The ICST calculations for IL/A suggest that the copper lead IL/A should be 3x106 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 106 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. CM-26 Cooler and Lead Test

12. 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 DT in the drop-in joint was 1 to 2 K. The DT 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 DT. • The copper plates for all of the MICE magnets should be thicker and the distance from the leads to the coolers must be minimized. CM-26 Cooler and Lead Test