Why 10,000 volts at altitude is a BAD IDEA

for the past six weeks i've been playing around with the world's smallest scanning electron microscope it's called an sem for short and it allows you to see things at a higher magnification than you could even with a really good light microscope the idea was that i was going to spend a week or two making a video showing off how to use it and then look at a bunch of iphone parts and other cool stuff but i've been having real problems with it from pretty much the first time i turned it on there's been issues with high voltage arcing inside it and we've spent a lot of time trying to figure out what's going on and it's proved pretty challenging but also super interesting let me show you a bit more of what's going on oh and thank you to brilliant for sponsoring this video we built a demonstration to show you what's happening inside the machine where we can all see it this is a 10 000 volt arc and it's jumping a gap of about four millimeters and it's pretty similar to what's happening inside the scm except instead of jumping between two balls it's jumping between random components and other bits of metal and as you can probably guess this is pretty bad for the machine we'll come back to this in a minute but why does an sem need such high voltage on a light microscope the photons from the light bounce off whatever we want to look at go up through the glass optics and get focused onto a sensor either a camera sensor like this or you know my eyes uh forming an image on an sem it works similarly but sort of inverted and using electrons instead of photons there is a beam of electrons that comes down and hits the sample whatever we want to look at here and that kicks off other electrons in all sorts of directions and some of those electrons hit a sensor which detects how many electrons hit it and the way we make an image is by scanning that beam of electrons back and forth across our sample and measuring at each point along there how many electrons hit the sensor more electrons make the image brighter fewer electrons darker so where does the high voltage come in we need the electrons to be going really really fast so when they hit the sample they hit it with a lot of force and kick off other electrons with a lot of force so that they're easier for the detector to detect and the way we get them going really fast is with an electric field so we set up two plates one positive and one negative and that creates an electric field between them that pulls the electrons down through it and gets them all going in the same direction really really fast the optimal voltage for this sem is 10 000 volts and the problem is that the high voltage is jumping through the air to other parts of the machine which is causing all sorts of problems now it's not like they didn't test this it worked fine when they sent it to me but i turned it on and all sorts of arguing so i sent it back to them they turned it on no problems they sent it back to me problems and at this point we were a bit stumped these sems have been all over the world including underwater and there's even one on the international space station what's different about my shop than literally everywhere else they've used it they asked if i have an ionizer in here i don't could it be humidity or lack thereof it's really dry here finally the ceo asked what altitude are you at and my shop is at around 7 300 feet which it turns out is higher than anywhere else they've tested it thus far but i hear you saying it's on the iss what the heck they keep the iss at the same pressure as sea level because of exactly issues like this let's go back over to the workbench and let me explain more this setup allows me to tweak various conditions there's a knob here that allows me to adjust voltage and then this readout here and this right out here are voltage and current between the two balls and this knob allows me to adjust the distance between the balls and measure it in a really fine-grained way i've gone ahead and cranked things up to 25 kilovolts so we can see a bit bigger arc and it'll be a little bit easier to see there are a few things that affect whether electricity will jump across an air gap so the first is voltage if i turn the voltage down the arc will stop uh secondly the distance matters so if if i make the gap bigger the arc will stop and if i bring it back together it'll start up again next the the shape of the electrodes matters so points make it easier for arcs to form and so even though you can't really see much there's actually current flowing here you can see on the current meter here and if i move it a little bit closer we might be able to see more so there's a little purple glow on the tip of the point but lastly the air itself matters what's in the air things like humidity and other particles or gases but importantly the pressure uh which changes with altitude and in general the higher the altitude the easier it is for arcs to form across longer distances at lower voltages but you don't have to take my word for it i'm going to drive this setup to some different altitudes and we'll see how the maximum distance between the electrodes changes when an arc forms but first what's really happening here at an atomic level my initial intuition about this was totally wrong so i built another demo to explain what's happening let's talk about electric fields this represents an electron right now it's just sitting here chilling and these represent two pieces of metal both of which have some electrons that are moving freely within them and let's say we start to move electrons from one side to the other creating a voltage difference and we call the side that has too many electrons the negative electrode and the side that has too few the positive electrode so electrons repelled by negatively charged things attracted to positively charged things so our free-floating electron now gets pulled towards the positive electrode now if we increase the voltage difference even further that electron goes faster and with more force okay this represents a gas atom we're going to say it's nitrogen because we're talking about air this is an electron that's in orbit around that atom and the atom really doesn't want to let go of it however if an electron hits it hard enough that electron can get popped out of orbit okay so we got the basics let's put it together and talk about how electric arcs happen so nitrogen atom chilling in space floating around between our two electrodes let's say something hits the negative electrode like an x-ray or a photon and causes one of these electrons to get popped off it gets pulled down towards the positive electrode and if it hits our nitrogen atom it can pop an electron out of orbit so now one free-floating electron has become two but what happens when we have a whole lot of nitrogen atoms floating around all with their own electrons it causes a cascade effect that multiplies and this is called townsend discharge or perhaps more athletes a town cent avalanche and one free electron turns into two which turns into four and then so on and this creates a flow of electrons between the two electrodes which is the electrical arc now not all of the electrons flow all the way to the positive electrode some of them rejoin a positively charged atom that's had its electron knocked off and when an electron rejoins an atom it lets off a photon which is light which is why we can see the arc so how do we prevent this from happening well as i showed with the high voltage demonstration if a number of things aren't just right it won't happen first if if the atoms are too far apart the electrons won't have a high enough chance of actually hitting something before they reach the other side second if the atoms are too close together then the electrons can't get going fast enough to pop an electron off third if the voltage difference between the two sides isn't big enough or the two sides are too far apart the electrical field won't be strong enough to get the electron going fast enough to hit an atom and pop off an electron in our electrical arc demo we can move the two electrodes further apart or we can turn the voltage down or we can add some insulation between them but what about the spacing of the atoms that's air pressure and air pressure changes with altitude so up here at 7 300 feet the atoms in the air are further apart so the electrons have more space to get up to speed which makes it easier for them to pop electrons off atoms causing electrical arcs to form and when they were designing the sem they tested it close to sea level and they did add some safety margins which were sufficient when they've tested it places like denver which is at around 5000 feet but apparently 7 300 feet is high enough that it's over the margin of safety but don't just take my word for it let's go for a drive and actually test this at different altitudes we're going to crank it up to 25 kilovolts so we can see things a little bit better and here in the shop at 25 kilovolts the maximum distance that an arc starts is at about 10.2 millimeters so let's hit the road and see how it changes based on altitude [Music] so [Music] i'm here at the top of the pass between pikari's pueblo and the town of mora down there uh it's about 9 400 feet here and because the air is less dense at the shop the ark should travel further so let's see sure enough the ark now starts at 11.3 millimeters instead of 10.2 down at the shop now let's drive down to a lower elevation and it should get shorter [Music] and now i'm at 4 000 feet uh just a little ways from the town of tucumcari new mexico which believe it or not is about as low as i can get in a day's drive from my shop let's see what it is here 9.2 millimeters so coming down to 4000 feet it's already down to 9.2 millimeters uh which is is more than a two millimeter drop here so that's you know it's pretty substantial given the the you know distance we're talking about and if if we went all the way down to sea level it would be even more substantial wow that's amazing i wish i could test this at sea level but even from 4 000 feet to 9 400 feet there was a 28 increase in the distance in our could jump so even if you build a pretty healthy safety margin into your design you can see how altitude could eat into that pretty quick so how do we fix it first we can decrease the voltage which is what we've been doing but the sem doesn't really work well at lower voltages we don't get as clear and sharp an image second we can add better insulation instead of relying solely on air third we can move things further apart and lastly we can make sure everything around the high voltage is nice and smooth so there's no sharp points that make it easy for an arc to form this journey has really inspired me to brush up on my physics particularly around electricity and electrical fields i took a number of physics and math courses when i was in college but that was a long time ago and honestly i'm a bit embarrassed about how much i've forgotten and going and watching a video or skimming through an article isn't really enough if you're like me and chances are if you watch strange parts you probably are you need to get hands-on with something to really learn it which is exactly what brilliant allows you to do it has sequences of puzzles and problems that take you from knowing nothing about a subject to a deep understanding in small bite-sized chunks and if you get an answer wrong it tells you exactly why so you can correct your misunderstanding they cover all sorts of different areas of math and science including electricity and magnetism so if like me this video has inspired you to dive more into the fundamentals of how electricity works i encourage you to check it out to support strange parts and give brilliant a try go to brilliant.org strangeparts and sign up for free the first 200 people that go to that link will get 20 off their annual subscription so when are we gonna get to see this sem work i don't know the manufacturer is still working out exactly how to fix it after many many attempts i'm running out of time to spend helping them try and fix it but hopefully i'll be able to make a video showing it off even if it's not working perfectly i'll see you again soon

Channel: Strange Parts

Views: 373,088

Keywords: high voltage, high voltage arc, strange parts, electronics, scanning electron microscope, scanning electron microscopy, microscope, altitude, high altitude, physics, electricity, voltage, electron microscopy, electrical engineering

Id: MIqK45nxcTo

Length: 13min 34sec (814 seconds)

Published: Sun May 23 2021