Analysis
This puzzle can lead to a lesson(s) that connect the rate of gas removal
the vacuum pump has to the rate of gas appearing in the chamber because of a
leak (gas entering the chamber from the outside) or from a fixed amount of gas
trapped in the materials within the vacuum environment (outgassing). This connection uses the mass transport and
energy balance STEM concepts. The energy
(power if normalized with time) available from the single stage pump to remove
the gas from the chamber walls established a steady state vacuum (value defined
by the flat part of the blue triangle plot) in the chamber. The two-stage pump has a greater pumping
speed (more energy per second) thus; this pump can pull more material faster from
the walls. (Students can use the two
plots to calculate and then compare the two pumping speeds.) Thus, if outgas type material exists, the
pressure in the sputter deposition chamber will start to drop sooner when the
two-stage pump is used. The natural technology
extension to these science and mathematics concepts is a review of the mechanical
construction of a single and double stage pump to see why the two stage pump
has a higher pumping speed. Ask if the
pumping speed for the 2-stage pump after outgassing will be the same as before
outgassing began. This is a good way to
push student STEM knowledge as it relates to pump mechanics and gas behavior.
Solution
The Tech now knows that the
vacuum system is "outgassing". YES
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