1. Cooling the Cloud Chamber Shane Spivey UTA Cloud Chamber Cooling Team

2. Outline Brief explanation of cloud chamber Motivation Design requirements Design considerations and tests Conclusions

3. The Cloud Chamber Uses a supersaturated layer of vapor to detect ionizing radiation Can see tracks of subatomic particles, and study how they bend in a magnetic field Using a cloud chamber, Carl Anderson discovered the positron by observing the track it made

4. Motivation To build a working, continuously running cloud chamber for public display in the new Chemistry and Physics building To inspire and inform people about the importance of physics To gain experience in working with a group to design and construct a large-scale physics experiment To bring notoriety to the UTA physics department

5. Design requirements for the cooling system Create a temperature gradient of 100° C Produce a bottom plate temperature of about 70° C Run in perpetuity Require only infrequent maintenance Cost a reasonable amount Be safe for public interaction Be aesthetically pleasing

6. Design considerations: Thermoelectric modules Chosen for original 10-layered cloud chamber design Powered by only electricity Wafer-thin design Cooling power too small

7. Design considerations: Liquid cooling Most common method of refrigeration, compression/expansion Need liquid with very low evaporation point, like nitrogen Dangerous and difficult to build

8. Design considerations: Liquid cooling We tested the surface of an aluminum cold plate with liquid nitrogen running through it

9. Design tests: Liquid cooling, kerosene pump test Pump worked but froze up after 10-20 seconds We increased the voltage from 3V first using tape and wire, then a DC power supply At 12V or higher it didn’t freeze At any voltage, the heat from the pump caused the nitrogen to evaporate rapidly

10. Design tests: Liquid cooling, gravity Using a simple gravity setup, the cold plate achieved -70° C after ten minutes

11. Design considerations: Commercial refrigeration Commercially manufactured By nature, large Costly, but still cheaper than building it from scratch

12. Conclusions The cooling requirements for a cloud chamber are monumental Construction requires expertise as well as equipment and facilities suited to the purpose Non-professional job has a high risk of yielding an unsafe end product Commercial grade chillers will be more effective, more economical, and safer