Cooling the Cloud Chamber
Shane Spivey
UTA Cloud Chamber Cooling Team
Outline
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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 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
Design considerations:
Thermoelectric modules
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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
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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