Cooling the Cloud Chamber

Shane Spivey

UTA Cloud Chamber Cooling Team

Outline

• Brief explanation of cloud chamber

• Motivation

• Design requirements

• Design considerations and tests

• Conclusions

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

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

Design requirementsfor 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

Design considerations:Thermoelectric modules

• Chosen for original 10-layered cloud chamber design• Powered by only electricity• Wafer-thin design• Cooling power too small

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

Design considerations:Liquid cooling

• We tested the surface of an aluminum cold plate with liquid nitrogen running through it

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

Design tests:Liquid cooling, gravity

• Using a simple gravity setup, the cold plate achieved -70° C after ten minutes

Design considerations:Commercial refrigeration

• Commercially manufactured• By nature, large• Costly, but still cheaper than building it from scratch

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