I am needing to perform an experiment on a radio signal, but need the extinction length (see Ewald and Oseen, for example) to be 250 meters or more. The extinction length at sea level in air (index of refraction about 1.0003) is a few millimeters. In free space (index of refraction 1), it is on the order of 2 light years. So, I need a good vacuum (not perfect) along the entire 250 meter run, and room at the end (large chamber) to house some test electronics.
Someone suggested multiple pumps along the run. My main concern is getting the pressure as low as practical so the extinction length (for a roughly 1 GHz signal) is near 250 meters.
Well, in principle particle accelerators are long tubes with excellent vacuum. Maybe this may be helpful:
https://cds.cern.ch/record/455985/files/p291.pdf
Thanks! I really think I may be good with 1-2 PSI, or maybe even up to 4 PSI. Just trying to get the extinction length for a 1GHz signal to 250 m or more. In fact, it probably needs to be on the order of 1-2 km or more to ensure I get the original EM signal at my destination.
Yes I can get you down to about 2.2 PSIA. Here is how you do it. You need a mixture of hydrogen and oxygen at one side of the tube. If you want about 50 PSI use 50CC Hydrogen @ 40PSIG and 25 CC Oxygen @ 40 PSIG. This will give you about 45 PSIA of pressure. Depending on the length you may have to drive it up a bit, but the shock wave will evacuate the pipe through the check valves. My pump is 40 liters and we could use it to drive the vacuum down in about a couple minutes or less. But don't use more than 70CC Hydrogen. Depending on the structure the shock wave could damage your wave guide. Is it metal?
Here is some data from the pump. After the shot in the video the pump body is at 2.2 PSIA. I love this pump....:)
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