It's about the same as the Earth's upper thermosphere where the ISS orbits. The ISS has to be periodically re-boosted to a higher orbit due to the drag from the Earth's thermosphere.
The moon has a harder vacuum than a tube, around 10-11 torr. The only reason it is that much is because of it's gravity. Actually, gravitationally it is capable of holding a true atmosphere and may have billions of years ago, but it's lack of a magnetic field and it's proximity to the sun has caused any atmosphere it may have had to be blasted away by the solar wind eons ago. According to the literature, interplanetary space is only around 10 molecules per cm3, but that doesn't count the particle flux from the sun. Still, it's way lower than anything we can achieve here on earth. Interstellar space is even less (except for stellar nurseries), and intergalactic space is a few orders of magnitude less yet.
The moon has a harder vacuum than a tube, around 10-11 torr. The only reason it is that much is because of it's gravity. Actually, gravitationally it is capable of holding a true atmosphere and may have billions of years ago, but it's lack of a magnetic field and it's proximity to the sun has caused any atmosphere it may have had to be blasted away by the solar wind eons ago. According to the literature, interplanetary space is only around 10 molecules per cm3, but that doesn't count the particle flux from the sun. Still, it's way lower than anything we can achieve here on earth. Interstellar space is even less (except for stellar nurseries), and intergalactic space is a few orders of magnitude less yet.
Well, if you want to use standard units then you should be using Pascals, not mmHg. The Torr is still very widely used in high vacuum science so that is what I choose to use. Since one Torr is approximately equal to one mmHg it isn't like you need to convert when we are discussing general vacuum levels.
I only use Fahrenheit when talking about the weather here in AZ. During the summers here, 43° just doesn't sound as hot as 110°
Yup. Typically, the tip-off operation was done with a small radial multi-flame gas burner. The hot glass would collapse inwards due to the vacuum (releasing an annoying amount of gas in the process) and the stem would be separated from the tube.
With all this useless knowledge, I need to get investors to start a small tube factory. By using modern automation and smart fixturing it would be possible to run relatively small lots of different types economically. Heck, it can even be done in an environmentally sound way - despite what most people think, making tubes uses FAR less toxic/hazardous/difficult-to-dispose-of materials vs semiconductor manufacturing
All the high vacuum meters I've seen are marked in Torr 10^-x units or Pascals. Never see mmHg. How about microns of Hg or microPSI for something obscure. I'm well along setting up a vacuum system for trying out heaterless tubes. Despite getting a turbo for $100 on Ebay, the turbo controller, fittings, seals, clamps, vacuum grease, TL011 turbo bearing oil, backing pump, and backing pump oil, exhaust filter, foreline trap, and TC and Ion gauges and elect. feedthroughs , and a leak detector run the cost into the thousands in the blink of an eye. Really should include a quadrupole mass spec in there too. (these are Ebay costs too, new catalog stuff would be in the $100,000 range easily) Then there are the tube manu. related costs yet.
"By using modern automation and smart fixturing it would be possible to run relatively small lots of different types economically. "
That will get you into the multi-million dollar range instantly. Instead of glass tip off sealing, I suggest using a spot welded small metal tube like some specialty IC's. Eliminating the glass bulb stuff altogether and using off the shelf pre silver-solder "tinned" ceramic mil/hybrid IC packaging would be a big savings (for setup costs) too, but may have difficulties with gettering or vacuum volume.
"By using modern automation and smart fixturing it would be possible to run relatively small lots of different types economically. "
That will get you into the multi-million dollar range instantly. Instead of glass tip off sealing, I suggest using a spot welded small metal tube like some specialty IC's. Eliminating the glass bulb stuff altogether and using off the shelf pre silver-solder "tinned" ceramic mil/hybrid IC packaging would be a big savings (for setup costs) too, but may have difficulties with gettering or vacuum volume.
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There's the germ of a very good idea here, just need to find the venture capital..
Yeah, that'll happen. Nobody would invest in such a venture when there are already established factories overseas capable of churning out usable tubes using cheap labor.
Interestingly, most of the materials needed are still available here in the US. Tubes use basic materials that are used in other industries, but even specialized materials like cathode coatings are available from many sources. The one material that would be a show-stopper is the plate material used in many power tubes from about 1960-onwards. There are numerous companies doing explosive cladding, but that particular combo hasn't been made since the 80's. A startup would need to commission a run of the material, which I'm sure wouldn't be cheap due to minimum quantities...
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You can't eliminate the glass bulb. Besides their performance characteristics, tubes need to look like tubes for aesthetic reasons. Plus, they need to be replacements of existing types capable of fitting in existing sockets. The glass components of most tubes are relatively cheap and glass is easy to work with, clean, and evacuate.
Hey there,
my UHV system at work operates at a typical base pressure of 1-2*10^⁻10 mbar, achieved by ion pumps and titanium sublimation pumps. Turbopumps are also installed, but I only use them during bakeout - they do not really work down to the 10^⁻10 range, unless backed by another turbopump before the backing pump - which is expensive.
Ion pumps and sublimation pumps have an enormous advantage - they are 'closed' systems and unlike turbopumps, do not flood your system with air in case of failure.
Pressures in the UHV range are usually measured with ionization gauges: They operate a hot filament (tungsten or low-temperature emissive coatings like in tubes) and accelerate the electrons towards a grid structure. The current of ions produced by the collision of electrons with gas atoms is a direct measure of the pressure in the chamber. The lower pressure limit for ion gauges is set by the 'X-ray limit', which is is caused by the electrons hitting the grid without colliding with gas atoms before and producing X-rays disturbing the ion detection.
Greetings,
Andreas
my UHV system at work operates at a typical base pressure of 1-2*10^⁻10 mbar, achieved by ion pumps and titanium sublimation pumps. Turbopumps are also installed, but I only use them during bakeout - they do not really work down to the 10^⁻10 range, unless backed by another turbopump before the backing pump - which is expensive.
Ion pumps and sublimation pumps have an enormous advantage - they are 'closed' systems and unlike turbopumps, do not flood your system with air in case of failure.
Pressures in the UHV range are usually measured with ionization gauges: They operate a hot filament (tungsten or low-temperature emissive coatings like in tubes) and accelerate the electrons towards a grid structure. The current of ions produced by the collision of electrons with gas atoms is a direct measure of the pressure in the chamber. The lower pressure limit for ion gauges is set by the 'X-ray limit', which is is caused by the electrons hitting the grid without colliding with gas atoms before and producing X-rays disturbing the ion detection.
Greetings,
Andreas
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