Heater Panel Testing

1. Heater Panel Testing Alexis Smith September 17, 2002

2. Objectives Heaters must maintain the pixel support tube outer surface above the cavern dewpoint of 13 C while cooling circuits are on. Target minimum temperature is 15 C. Create conservative experimental model of the physical system. Verify function by cooling inside of shell and recording temperature profile of shell surface at various heater power levels.

3. Experimental Setup Simulates a section of the PST with external heater panels providing 250 W of heating at full power and internal barrel shell at –23 C System components: • Internal cooling unit -- 6 meters of copper tubing coiled to 300 mm diameter, wrapped in foil, coolant enters at –25 C • Insulated endcaps

4. Experimental Setup System components (cont’d) • Composite shell -- diameter: 456 mm, length: 300 mm • 5 heater panels, equally spaced. Heater traces connected in series. Heater panels connected in parallel . Each panel has ~50 ohm resistance (1 Amp per panel at max power). Thermal images taken with IR camera

5. Results Testing confirms that heater panels perform adequately • Shell surface temperature can be maintained at 15 C or greater at 30% power • Surface can be heated well above 13 C at higher power levels • System can achieve target with some defects in panels

6. Test Results: 30% Power Lowest power level at which minimum shell temperature is above 15 C with “barrel” at –25 C. Maximum shell temperature: 32.5 C. Internal gas temperature at midline: 14 C. (non-uniformity in surface temperature along length because coil is not straight)

7. Test Results • Heaters achieve greater temperatures than required at high power levels • Sharp temperature gradient exists across surface due to natural convection • Internal air temperature rises as surface is heated

8. Simulation of failure modes Low Power High Power Effect of 2 outer traces missing on a panel is minimal and only observable at high power. It does not prevent the attainment of specification.

9. Simulation of failure modes Center panel disabled (50% power, coolant at –18 C) Normal (60% power, coolant at –25 C) Disabling an entire heater has a significant effect on the temperature profile. A higher power level may be required to achieve the specification, depending on the heater location.

10. Summary Conclusions Heater panels can maintain PST surface temperature above 15 C Large temperature gradients exist due to natural convection Recommendations • Connect heater traces in parallel to avoid complete panel failure resulting from a single trace defect • Use two or four separately powered panels for a more uniform shell surface temperature • Top: low power • Bottom: high power • Middle: medium power • Place temperature sensors on heat panels to provide feedback for required power level