hckrnws
> [xenon is] great for in-space propulsion because it’s fairly heavy (so you get more ooomph per atom)
More specifically, for a given exhaust velocity and grid spacing, the space charge limited thrust density (thrust/area) of an ion engine scales as the square of the mass/charge ratio of the ions. So you really want heavy singly charged ions. This is completely unlike thermal rockets, where you want low molecular weight exhaust gases.
Plasma engines that accelerate a quasi-neutral plasma aren't subject to space charge limits, but even there heavy ions help because they reduce the energy used in ionizing the propellant per unit propellant mass.
BepiColombo [0] uses 581 kg of Xe gas for its electric propulsion. I remember reading at the time this was being built that it consumed a measurable portion of the global xenon production for that year. This post reminded me to look that up, and it seems to be only ~1% of the ~50 tons, which is quite a bit less than I remember but still quite significant for a single application to use a non-trivial amount of the supply.
[0]https://sci.esa.int/web/bepicolombo/-/60642-bepicolombo-mtm-...
Given that ~100 million tons of oxygen are produced annually, extracting all the xenon from that air would yield about 170 tons/year. So there's a bit of room for growth.
The BepiColombo number is similar, I think, to the amount of xenon made annually in nuclear reactors (where it occurs in spent fuel as the result of fission.)
I think it might have taken a larger percentage of high-grade ultrapure xenon, a narrower market than the global bulk supply. A 1% impurity is fine if you are using xenon for welding, not so much if you are firing zenon plasma at a grid carrying a few hundred volts. A little bit of o2 in there and your grid would be rust very quickly.
Does anyone use xenon for welding? Argon, yes, but xenon is five orders of magnitude less common in air.
You could. It is heavier and so can carry more heat. There may be some specific metal/tool combo where that might be needed.
Inert gas in welding isn't used to carry heat, it's used as shielding to prevent oxidation, nitridation, and ingress of hydrogen. In any case, the heat capacity of the noble gases are almost identical. What xenon might do is reduce diffusion of heat away from the weld, as its thermal conductivity is just 1/3rd that of argon.
In practice I think a combination of argon and CO2 is typically used for inert gas welding of steel.
It depends on the process. Argon/CO2 is used for MIG welding, while TIG generally uses pure argon. In some situations that justify the expense, helium is used instead as it allows deeper weld penetration.
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Isn't getting nobles to actually ionize pretty energy-intensive though?
Sure, but one still has a savings if one goes to heavier noble gas elements over the lighter ones. The noble gases are used because they don't contaminate spacecraft surfaces.
About the only place I can think of in a plasma engine where you'd want to use light elements is if the engine is thermal: making a confined plasma, heating it to very high temperature, then expanding it through a magnetic nozzle. There, you'd want to use hydrogen to minimize radiative losses from the hot plasma, especially vs. using a plasma containing partially ionized atoms of higher atomic number elements; these can radiate fiercely.
Wearing this as an actual crown might leave one feeling light headed
I'll get my coat
Not loading for me, archive here: https://web.archive.org/web/20250320114939/https://theshambl...
If you're into gas displays, there's also the plasma toroid (not globe).
People have be filling it with different gasses to get different colors.
A few safety PSAs on these:
1. This puts out a fair amount of UVC light. Most people are not familiar with this hazard because the atmosphere filters it, but even a modest flux can degrade your eye lenses and give you cataracts. Get a set of safety glasses that explicitly say they block UVC if playing with this for more than a minute or two cumulative. Normally you would use borosilicate glass to filter it, but I would not trust these to use anything other than the cheapest materials.
2. The hazard is "high voltage" but it is 1 MHz, not DC. Conventional wisdoms on DC high voltage insulation isn't sufficient. You need RF safety guidance. If you get your finger within about an inch of the terminals the air will break down and turn your skin into a 50W load. It will smell a lot like burnt plastic, but it is your skin that's been burned. Treat these with respect. They are inherently unsafe because they do not have engineering controls to keep touches away from dangerous locations: a knife with no handle.
In case anyone's wondering: no these aren't really above the level but few enough people are getting hurt and [insert your preferred explanation why society doesn't meet demands] that nothing happens.
Be safe, have fun.
Unless its quartz glass or something wouldn't it be blocking pretty much all of the UVC?
Yes I'd wager they're soda lime and ought to filter it. In absence of knowing the material, it's a hazard that can be mitigated with cheap PPE. Everyone can make their own choice, as long as it's informed.
Seems too inexpensive to be made of quartz to transmit the UVC. Typical glass will absorb it, possibly fluorescing a bit in the visible.
I wonder how this one works: https://youtube.com/watch?v=xlcywgEMuGI
Those looks like LED strips inside of frosted tubes. The connectors on the bottom are similar to 3 prong connectors used in LED strips.
It’s nice to see this guy getting some attention for a different reason. Maybe something good will come out of this whole debacle.
It took some digging to figure out what the debacle was. Is this it? https://vuink.com/post/penool-enguoha-d-dtvguho-d-dvb/mjrath...
Also the top story on HN right now: https://news.ycombinator.com/item?id=46990729
Posted half an hour after my comment. That is oddly specific timing.
It's amazing that we're getting this now, I don't understand what the prompt was that made the AI take offense at the closed PR, but I also must say, it does have a point.
I don't blame the maintainer, though, I think it's a very understandable reaction to close the PR.
If I am understanding it right, the maintainer wants human-readable, human-maintainable code even if it is slower than the AI output. As someone who has to maintain someone else's "clever" code, I have to agree with him.
And there are specific "low impact" easy issues that they want humans to solve, so they can get experience and become better devs.
Having the AI do all the easy grunt work removes that ability.
I disagree that the AI can't make human readable/maintainable code if prompted properly, but yeah, just throwing the Claude output up on a PR isn't valuable.
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I purchased one of the Lumora gas displays and it works well. Simple enough to build yourself (laser cut, 3d print) if you have the gas filled tubes. Fun to have my kids guess what color a gas will glow.
> (sorry Radon and Oganesson)
With Radon it might even be conceivably possible (not sure how hard it is to get and if any restrictions apply because of its radioactivity), and it would work for a few years, because it has a half-life of 3.825 days (EDIT: this is of course complete nonsense, the "." is a decimal point, so it will only work for a few days). In the quantities needed for a gas tube (and as long as it stays in the tube!), I guess it should also be relatively safe, but I'm not an expert. Apparently it produces red light when used in a tube. Oganesson however has a half-life of 0.7 ms, so, aside from how expensive it would be to synthesize enough of it, it's doesn't stay around long enough for any experiments...
A few years with a half-life of less than four days? I doubt you could perceive any glow after more than a few weeks.
In a year the radon would've undergone about a hundred halvings, so around one 10^30th of the original radon nuclei would be left. Which is to say, almost certainly zero. One mole worth of radon would've decayed down to the last atom after less than 300 days (mostly to lead-210, which would then comparatively slowly decay to stable lead-206 with a half-life of about 22 years).
Ah, sorry, I'm actually from Germany, so I interpreted the "." followed by three digits as a thousands separator. My bad...
Ah, yeah, if it were 3800 days it would work fine for a few decades =D
Beautiful. Noble gases are so cool.
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