Cooling the Cloud Chamber

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

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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

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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

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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

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Design considerationsThermoelectric modules

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

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Design considerationsLiquid cooling

• Most common method of refrigeration,
  compression/expansion
• Need liquid with very low evaporation point, like
  nitrogen
• Dangerous and difficult to build

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Design considerationsLiquid cooling

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

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Design testsLiquid 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 didnt freeze
• At any voltage, the heat from the pump caused the
  nitrogen to evaporate rapidly

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Design testsLiquid cooling, gravity

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

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Design considerationsCommercial refrigeration

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

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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