Fun with Plasma Tubes!

hi today we're going to begin a series of videos on fusion thermonuclear fusion energy [Music] [Music] it used to be a joke around the physics community you know those wild and crazy physicists and the joke went that fusion energy is always 50 years in the future no matter what technologies we developed no matter what problems we solve who always discovered new challenges and new hurdles and so it always remained a tantalizing goal a couple of generations in the future but that has changed and what has changed that is this this little thing here this is called red Co tape re be Co and it stands for rare earth barium copper oxide superconducting tape the fact that this is a high-temperature superconductor is merely icing on the cake what makes this such a game-changer we're going to get into a little bit later but I predict that based on what's going on that we will be seeing fusion energy in as little as five years and the reason Fusion is so significant so important is that the amount of energy available through fusion is absolutely astronomical if you took a look at the video that we did about six eight weeks ago where we did hydrogen detonation we burned hydrogen and oxygen in small balloons and we produced some really impressive explosions and flashes if we took those same balloons and we filled a merely with hydrogen and caused a fusion reaction you would have seen the same explosions the same flashes from nearly 2,000 times farther away many miles away now any kind of an element can be fused and you can create larger nuclei from smaller nuclei and what's interesting is as long as the final product has a lower atomic weight than iron you'll get a great deal of energy out of it interestingly if the final product is a heavier element than iron it actually absorbed energy in the process of fusion and that's why in cosmic nucleosynthesis you really can't develop large atomic weight nuclei unless you have a tremendous amount of energy around you that's why that occurs primarily in supernova explosions on earth the simplest fusion experiment or fusion process that you can you can perform is on hydrogen now hydrogen like any element is named based on the number of protons hydrogen has one helium has two lithium has three beryllium has four and so on and so on however if you add a neutron to common hydrogen to the common proton you create what's called heavy hydrogen or deuterium and if you made that into water you'd create what's called heavy water and it's not a funny interpretation of the word heavy it's literally heavier you could feel the difference if you took two flasks filled with the different materials deuterium is not radioactive it's common on the earth it's relatively easily obtained and it probably would be safe to drink if I was daring or I was Cody I might be willing to do it it is the primary ingredient for fusion because when you take deuterium and you add a second Neutron and this can be done within a reactor you create what's called tritium tritium is an isotope of hydrogen that is mildly radioactive it has a half-life of about ten years and it will generate a little bit of radioactivity but not a tremendous amount of radioactivity and that you can't handle it and you can't contain it but because it is so rare on the surface of the earth it would be a bit of a barrier to fusion energy however the reactors that process the deuterium and the tritium actually can generate more duty tritium than they consume in the process of absorbing the heat and operating so all you really need to do is provide fresh deuterium to a nuclear reactor and it would read and it would be able to run for hundreds of millions of years based on the amount of deuterium on the earth now the process of fusion is actually very simple it's not complicated but it's hard just like breaking the world record with 100-yard dash it isn't complicated it's simple just run faster but it's very hard and what makes fusion hard to perform is that the two nuclei the deuterium and the tritium that you want to fuse into helium are positively charged they repel each other and so you have to push them together to get them to link and you can't do that mechanically unless you've got the gravitational force on the inside of a star the only way that you can get them close enough in order to form a new nucleus is you have to fire them at each other at with sufficient velocity that they will get close enough that they can overcome that repulsion and link up and when you're talking about speed or kinetic energy or velocity in any kind of matter you're talking about temperature so on the surface of the earth in order to get deuterium and tritium diffuse you need to reach a temperature of about a hundred and fifty million degrees that's what makes it so hard no known material could contain it and even if you could contain it the problem is the container itself would cool off the hydrogen isotopes and you wouldn't be able to get the fusion so the two approaches that have been taken over the past 50 years to try to create a fusion reaction have been inertial confinement fusion and magnetically confined burning plasmas now I love lasers you take a look at our videos over the years I've built and owned some pretty impressive lasers I love them and inertial confinement fusion is dependent on lasers effectively what happens is some of the world's most powerful lasers will focus their energy down on a very tiny particle called a hole Iram and when they do so they create so much heat at that point that they cause the outer surface of the particle to blast away and because of Newton's law of opposite and equal reaction the inside of that hole Iram that contains the deuterium and the tritium are compressed and heated to millions of degrees and fused and the reaction does you actually produce fusion particles when you do this the reason that this approach I believe will never be practical is that there are two major obstacles one the biggest lasers in the world can typically cycle it may be two or three pulses per day and in order to get practical energy out of the system you're going to have to operate them at kilohertz frequencies so we are way away from any kind of technological breakthrough that would allow us to produce that kind of frequency and that kind of energy but there's a more fundamental problem because with inertial confinement fusion all of the energy necessary to create that compression has to be generated each time you blow up one of these little hole roms so all of the power that you generate in your process has to be sent through the grid it has to be stored in capacitors has to be fired into the lasers and reintroduced into the system every time you try to explode it the difference with magnetically confined burning plasmas is that once you get the plasma hot enough it keeps itself hot it is self-sustaining and so all you really have to do is squirt it in a little bit of deuterium and a little bit of tritium and the reaction would run forever now the problem though is that you have to contain these materials you have to keep them within a volume and in order to do that you need to use magnetic confinement you have to take advantage of the fact that these protons as charged particles can be manipulated by magnetic fields and that is where of the revco and the superconducting advancements are going to make it possible for us to contain those burning plasmas now one thing you may wonder about is wait a minute you said if you take the two positively charged nuclei and you get them close enough together they'll link up well why they're always positively charged they should never want to be together and as a matter of fact why does any nucleus that's filled with a bunch of positively charged protons stay together the reason for that is what's called the strong nuclear force effectively opposing the repulsion of the Coulomb repulsion positive to positive there is a very strong much stronger attractive force called the strong nuclear force but that force unlike Coulomb repulsion drops off far more quickly Coulomb repulsion drops off as the square of the distance you go ten times farther away you get 100 the amount of repulsion the strong nuclear force drops off as the fourth power of distance you go ten times farther away and it's ten thousand times less effective at attracting the two nuclei so until you get the nuclei close enough together that the strong nuclear force dominates they won't stick and that's why we have to get them as close as we do now the interesting thing about the whole idea of the burning plasma and thus and the magnetic containment is that in order to create the kinds of environments that you want to create fusion you need to produce a plasma in order to produce the plasma you need to understand something about a couple of technologies and so that's what we're gonna do in this video today is I'm gonna show you how to cook up a plasma right at home for relatively low cost and the two technologies that you're going to need to know about our high voltage and vacuum now the kind of voltages that we're gonna need to work with here are on the order of a couple of thousand about 1500 to about 3000 volts but we don't need much power we're talking about a couple of milliamps or just a few watts nevertheless it's dangerous if you're not familiar at all with electrical safety you might want to get somebody that can help you with that or just be very very careful because this can still be lethal if you don't handle it right a lot of times we talk about grounding things in order to keep things safe to give electricity a good way out but one of the things that you don't want is you don't want to become the ground you don't want the electricity to flow through you so one of the safety rules that I'd always recommend when you're dealing with high voltages is to use what's called the one hand rule that when you touch high-voltage components you don't have a means of the power to be able to travel through you through your heart through your thorax and in addition you've got to keep a very close eye on things because in dealing with plasmas we're not only dealing with high voltages but we're gonna be working in the dark so safety safety now the simplest easiest way to generate a high voltage for these kinds of experiments would be to get what's called a neon sign transformer these are easily available on eBay for a few dollars this this is a big one it's an old surplus neon sign transformer and what makes these nice is that they are what's called ballasted unlike say a microwave oven transformer a MOT this thing will simply keep drawing power until you blow the circuit breaker it'll just keep pulling power into it there's no limit this has an integral resistor so that even though it's still quite dangerous it won't just keep pulling more power so it does reduce the risk a little bit another interesting feature of a neon sign transformer is its what's called center tapped in a microwave oven transformer and many step-up transformers you have sort of a low voltage lead and the high voltage lead that's not true on a neon sign transformer effectively both of the leads that come out of a neon sign transformer are hot or high-voltage so what happens is the two leads are actually operating on either side of the neutral white lead so you can't handle any of these leads both of them are going to be dangerous but if all you want to do is get a plasma to glow this is really all you need is a high voltage source hooked up to your wall now the problem with this though is this thing have produced about 450 watts it's way more than you need one of the things that I would highly recommend is what's called a very AK it is an auto transformer or a variable voltage transformer you can get something like this this model here which is about $100 handles a kilowatt of power and will vary the output voltage anywhere from zero all the way up to sometimes a multiple of the line voltage very convenient not only for running signed the neon sign transformer but you can use it for heating elements you can use it for motors you can use it for a variety of different applications they're very nice to have in this case because we can dial the output voltage of this down to maybe teen or twenty volts we can keep this down it may be 1,500 to 2,000 volts which again limits the risk and just keeps the tubes from getting really hot so these things I think would be very useful if that's what you want to do is just produce the plasma now if you want to step it up a little bit more one of the things that will happen with this is because both leads are going positive and negative opposite each other both ends of the tube are going to effectively look the same because each one is participating in the positive and the negative output of the transformer but because there are a lot of changes or things that happen with high voltage where you actually want to see what happens at the negative and the positive end the cathode and the anode end you might want to consider using a rectifier to change this to a direct current as opposed to an alternating current into your plasma tube now a rectifier is based on diodes that are effectively one-way valves for electricity they only allow electricity to flow in one direction and in this setup that we have down here on the table we've placed four of these diodes in order to create what's called a full wave rectifier these diode stacks four of these are very inexpensive you can obtain one of these that I've got in my my right hand here for about six to eight dollars on eBay and this one as you can see is rated for 40,000 volts at one amp it's a 40 kilowatt rectifier it's way overkill for this application but for $35 you can have a nice full wave rectifier for high-voltage experiments now the way the rectifier is wired up is one of the leads from the high voltage transformer travels to two of these rectifiers the other lead from the high voltage transformer travels to the other two leads of the other two rectifiers so for example when this one is positive it feeds into both of these rectifiers but only this side is able to flow power this one blocks and alternatively if this one for example is positive and feeds into these two rectifiers only the side that when this only when this is positive can power flow out this way when this side is negative it can only flow out this way so this side is the cathode always going to be negative this side is the positive always going to be the anode and so these two leads leading into here lead into two filtered leads coming out here to go into your plasma tube now you're getting a direct current but it's still pulsatile essentially the power is coming out in pulses 60 times a second and four people are a little familiar with electronics you might say well we could smooth this we could actually put a little capacitor here and kind of smooth out this peak and turn it into a nice even output you can't with a plasma tube because a plasma tube essentially is a has a negative resistance now this isn't free energy or better than a superconductor what it means is that the charge carriers what's carrying the electricity is generated by the electricity so the more current we put through this the more charge carriers we generate and the more current we can carry so effectively if you hook up a capacitor to this what it will simply do is charge the capacitor up to the discharge limit of the two and then you'll get a flash so instead of getting this pulsatile sinusoidal up and down you're gonna end up getting flashes like a repetitive strobe light or a flash tube it's not gonna smooth out your current in order to get smooth output at high voltages you're gonna have to add an inductor and a resistor you don't need to go there not for this purpose you can get away with just the neon sign transformer you can do a lot better if you add the very act to it you can see what's happening to the cathode and the anode if you do a rectifier stack that's enough now the second technology that you're gonna need to know about is vacuum now we've got some really big vacuum pumps next door for our lasers Edwards wealth do a seal but I've really started to like these very inexpensive HVAC pumps that you can get on eBay or Amazon for like $100 what I like about them is they're relatively convenient obviously they're inexpensive I also really can recommend the Yellow Jacket pump that we have here it's very well built it's very solid and it has a very good capacity it's a two-stage pump will pump five cubic feet per minute about a hundred liters per minute and can reach a specified maximum vacuum of 25 microns but we found when we actually put a meter on this thing this thing will actually get down to 6 microns it's under SPECT which is pretty unusual for an inexpensive pump like this the only problems with these types of pumps as opposed to the high-end pumps is when you turn them off they will immediately back fill with air you'll fill your whole system up in maybe 10 seconds with air they don't seal when you turn them off so you're gonna need to include a valve now this is a specific vacuum valve it's a ball valve like this but what makes it a vacuum valve is not only does it have no leakage it's made to work at a very high vacuum but it also has a large opening it's not a small opening and that's very important because in vacuum systems if you forgive the innuendo gurth is better than length because vacuum pumps don't suck effectively what happens is in order for a molecule to be pumped out of the system it has to just randomly bounce around inside the tube and then find its way into a little tiny port and then make its way all the way up this tubing until it gets into the pump and one of the pump vanes captures it and removes it from the system so if you have a very long diameter very tiny tube you're gonna be pumping a lot more slowly than you would if you had a big opening and a short distance to travel for example I have here a turbo molecular pump this is made for ultra-high vacuum and you can see how broad the opening is into the chamber and how short the distance that the molecules have to travel before they get captured and pumped and removed from the system now for this kind of a vacuum this stuff is tolerable but you want to do whatever you can to try to minimize obstructions and and shorten lengths now if you don't want to spend 60 or 70 dollars on a high quality ball vacuum valve like this there is a cheap way to do it that actually works pretty well a simple piece of silicon tubing and a clamp is actually a pretty effect low restriction valve that you can put on this thing and you would just clamp it off before you turn off the pump it's another reason why you don't want to use a pump like this as the sort of backing pump for a high-tech pump like the turbo molecular or a diffusion pump because if you lose power air will flow immediately into the system and you can damage and destroy these pumps so this is not good if you're gonna be using this in a more complex vacuum system another little issue is that all of these vacuum pumps almost all vacuum pumps operate under an oil bath both for a lubricant and as a seal and you can even see this little gauge here will show you the the oil level inside the pump what's pertinent is that the air that's coming out of the pump has a mist or a vapor of oil and it actually a mist a little droplets of oil and they can get into your room so if you deal with lasers and optics that's not so good so there's a neat little trick you can actually obtain I got this from Amazon for about twenty-five dollars and what it is is it's a hydroponics activated carbon filter and this got a couple of kilograms of activated carbon tremendous amount of surface area with a little soft on the outside to keep the dust in and then just a couple of pieces of hardware plumbing PVC plumbing and a soft pliable tube and so all of the vapor gets captured in here it'll even capture organic vapors so there's absolutely no aroma no vapor no mess you can use this in your living room your kitchen you could use in your bedroom and nobody's got any excuse to complain now if you want to up your system a little bit more one of the things that you might want to consider getting is this this is a vacuum meter again yellowjacket I really like their stuff what this meter does is it allows you to measure the pressure in your system and you don't really need that because a lot of the endpoint of producing a plasma is gonna be visual but it's a nice way of diagnosing leaks it also allows you to for example add different gases to certain levels so it's a nice thing if you're upgrading to put a vacuum meter in there this particular one is nice because it will it's not destroyed or damaged by operating it at atmospheric pressure and will read all the way down a micron so it is a nice range for what we're doing and the only negative is it's about a hundred and fifty bucks so it's more expensive even than the pump and it's certainly not necessary but it's a nice addition another thing you want to think about is what's called a needle valve in order to be able to add gases into your system or control the flow of the gases a small needle valve like this about $25.00 from mcmaster-carr with a very small C V and what that means is the amount of flow that would go through it under specified pressures is very low so that this valve even fully open won't flow a great deal of gas you don't want that and with the needle precision of 20 turns you can turn this way way down and so you can just bleed in a little bit of gas at the same time that you're removing it from the other side to create variable pressures inside the system this one has a CV I think of 0.5 so it's very very low and it works very nicely and even if you don't hook this up to a tank you just leave this open to the air it again allows you to control the pressures very well you can use gases if you want to like we have oxygen here and nitrogen hooked up but they're not necessary in order to be able to produce a visible plasma in order to be able to play with it the plasma tube itself here is can be constructed for a couple of dollars if you don't want to go a little higher end like the one that we built here and it consists of a glass tube it can either be quartz like we're using here Pyrex or soda lime I would stay away from the soda line because it tends to be rather fragile and the ends tend to be brittle and it's it's easy to damage it in addition it's really not a cost savings over something like borosilicate Pyrex Chemex that material is excellent because it's tough it's harder to break in addition unlike the quartz tubes were using here it blocks UV deep UV which can be a little bit risky in an environment if you don't have the proper protection and there's no real advantage to the quartz over the Pyrex and you could get a Pyrex tube like this for a couple of dollars the stoppers on the end are made out of what's called bona and buna an which is a common rubber stopper and come pre-drilled or pre board with a small opening these are one hole stoppers if you place by press fitting a tube of either stainless steel copper or aluminum in here you have a way of getting the gas in and out you also have a way of hooking up these tubes as electrode so for a few dollars you've got a plasma tube and it's a very convenient way of getting the setup if you're just starting out now one of the things about a vacuum system is obviously you don't want leaks I mean that that goes without saying but in order to remove the gas from the system you have a couple of other sources of air molecules and water vapor that are not from the outside one of the sources is what's called surface D adsorption ad all of the surfaces in this room including me are covered with air molecules water vapor and in some cases of the pane solvents and they're in equilibrium with air pressures so as the air pressure goes up more of the molecules will stick to you electrostatically and as the air pressure goes down those molecules will bleed off into the environment and keep the pressure within the system now eventually they'll go away but they can present a flow of gas into your system that can last for a very long period of time so in order to try to reduce that one of the things that you want is you want as little surface area as possible and the way to achieve that is smooth surfaces you put activated carbon in here and you're going to be pumping for hours and hours trying to get the pressure down so smooth surfaces are a good idea there's another problem and that's called D absorption a B bulk removal of gases from materials now glass ceramic and steel won't have a problem with that but all organics do whether it's finger grease hair oils plastics rubbers lubricants all of them will give up boil off gases from their volume and that can significantly contaminate a vacuum or prevent you from reaching very low pressures so one of the things that you can control is cleanliness keep everything clean keep your fingers off of it wipe it before you use anything and that's gonna end up reducing the amount of that gas that can be released which it can't avoid though in these lower end systems is the organics now some organic materials are bad one of the worst is actually silicon tubing it it will release a lot of vapor into the system and it's not really a very good tubing to use for vacuum systems I'm using it on the output from the vacuum pump but you don't want to use it on the input unless you make it very short and you're willing to live with a higher vapor pressure another bad one is PVC if you're thinking about building say a plasma tube from a clear piece of PVC pipe not a good idea PVC will out gas for a long period of time nylon is pretty bad - anything that has an aroma is bad most epoxies and most glues are pretty bad buna in which were using for the stoppers here is not particularly good it's okay but it does out gas for a while and so that's something that you could upgrade to what's called a fluorinated rubber the o-rings that I'm using here and the o-ring in this conflict fitting are made out of what's called Viton it's a fluorinated rubber and it produces less outgassing you can actually reach medium level vacuums much higher than we're doing here and this is what this conflict fitting is made for in order to seal it's a window in order to seal vacuum chambers this Viton o ring is out gases not so bad that you can actually use this for medium level or medium high level vacuum systems however if you were going to go even further and you wanted to go to an ultra high vacuum system there is no rule for any organics in that kind of a system you'd probably replace this with a copper ring metal now there are better plastics though and one example of a very good plastic is polyethylene very inexpensive polyethylene doesn't out gas very much and that's why we're using it for these tubes even though it's kind of stiff it's a little bit of a hassle this is very inexpensive it costs about 15 cents a foot it's a heavy wall so it doesn't collapse under vacuum and it won't out gas very much and we can get from very good vacuums using polyethylene tubing as opposed to say the silicone or gum rubber the one of the problems with this tubing though is it is almost impossible to remove it it's very easy to put it on the holes Barb's and you'll get a very good fitting on a very good seal on here but I could probably hang from this too it's it's you can't get it off and you don't want to slice it because you could produce a little groove or a little notch in your in your fitting now this is so cheap that I wouldn't mind throwing away the tubing but the fittings might cost a little bit little trick with that put this in a vise take a heat gun put a little tension on this warm this up with a heat gun and after about thirty seconds this gets soft enough and pops right off so if you're using this tubing it's a nice trick in order to save your your components better yet captain tape captain is a good electrical insulator and it's used for a lot of electrical work it also has a very very low outgassing rate and it's a good plastic you can get it in bulk form to the very best plastic is actually polytetrafluoroethylene Teflon it's inexpensive it's easy to machine and that's why instead of using the rubber stoppers for this application here I used my lathe and turned down a little plug made out of Teflon and Teflon has very low outgassing so you can produce very high vacuums with it it's also an excellent insulator and if your electrodes get hot it can tolerate very high temperatures so it's an excellent plastic to use in a vacuum system so it with that in mind the only two things I want to sort of mention is that in this system because we clearly have an outside port for the gases instead of using a tube to get the gas in and out I used a solid rod and for that purpose I used an a welding electrode tungsten tungsten has an extremely low vapor pressure a very high melting point and so it tends to sputter less or essentially give up it's it's it's atoms under the impact of the electrons or the release of the electrons as you can see here even from an hour or so of use you create what's called a sputtering coating on the inside of the tube as the Teflon as the tungsten is driven off of the electrode under the impact of the electrons the reason I have this press-fit piece of quartz in here the electrode is because this piece of quartz I can cut a bunch of these off I can press this in here this will catch most of the the sputtered material keeping the inside of the tube clean you don't really need to use this but because you can't clean this off and this is a more expensive tube this is kind of a nice feature if you're going to be using this for long periods of time the tungsten is a little unusual in that I'm using what's called thorium doped tungsten it's fallen out of favor in the welding community because thorium is radioactive it's very low grade radioactive and so I'm not getting any radiation from it but if you cut it or you mill it or you grind it and you get the dust in your lungs not a good idea so when I fabricated these short pieces of tungsten electrode I went outside put on a mask put on a respirator worked up wind and effectively when I brought it in I was I wasn't going to contaminate the inside of the shop with the thorium there are other doping materials that can be put in these electrodes lanthum is another one and the reason that you dope them is because it reduces the amount of electricity necessary or electrical potential necessary to get the electrons into the tube and the lower the voltage the less the sputtering and essentially the lower the power that you can run your system at which makes everything a little bit safer a little bit easier so that's pretty much the setup here for what you would need if you want to go from super simple to more complicated and more features so now what I'm going to do is I'm going to go ahead and I'm going to put the Teflon plug in the end of the discharge tube here and then using the one hand rule even though I know the Transformers turned off unplugged I connect that guy up then I'm going to go ahead over here and I'm going to put this plug in this end of the tube and once again one hand rule hook up the cathode then I'm going to come over here and we're going to turn on the vacuum pump and I'm going to tell you to look at the end of the plug here when we begin to apply the vacuum so open the valve and on three two one on see how it sucks in now if you move over to the meter here you'll see that the meter is beginning to show a very rapid drop in pressure it's going down a millimeter or a second this process will continue but it will slow progressively asymptotic aliy the pressure will reach toward zero but never get there the reason for that is we're actually removing gas and because this is a positive placement displacement pump the amount of gas or the volume of gas pumped is the same all the time but the am number of molecules that are removed decreases as there is less per unit volume now right now we're already down to about two hundred and fifty two hundred and forty two hundred and thirty microns of mercury now this will continue for about four or five minutes as we continue to bring the pressure down and I'm going to let that happen so you can see what kind of ultimate vacuum you can get with the setup that I described earlier right now we're at about 150 and we're going to give this about three or four more minutes now it's been a couple of minutes and you can see that the pressure right now is at about forty eight microns and if we were let this go another five or six minutes we'd get down to around thirty five thirty four microns progressively we will keep dropping but this pressure already is much lower than we're going to need and it's due to the outgassing that I described earlier from the plastic and the surfaces of the of the tube we could accelerate the process if we heated the tube with heat gun to fifty to a hundred degrees centigrade for a couple of minutes we would drive more gasses out temporarily raise the pressure but ultimately remove gas from the system and the pressure would drop to its ultimate low level a little more quickly nevertheless as I said this is already low enough and so what I'm going to do now is max you're going to introduce a little bit of nitrogen so that we can fill the tube up to a couple of millimeters bring it up from 46 right now 45 and we're going to bring it up to a couple of millimeters I may have to juggle a little bit with this but you also hear that the sound of the pump changes slightly when the pressure goes up that's pretty good it's always a balance between the two when you're trying to control the pressures now what I'm going to do is I'm going to go ahead and I'm going to plug in the transformer we're going to turn the voltage on and you'll see what happens I'm going to adjust the very act now to about 24 volts in which means about 2,400 volts out and as you can see nothing happens that's because the air and the nitrogen actually acts as both an insulator and as a conductor in the neutral state air and nitrogen is an excellent insulator when the electrons coming off the cathode impact those molecules or those atoms it creates ions and that is a conductor but because we have a lot of neutral gas in here this is not able to conduct a discharge through the tube so what I'm going to do is I'm going to close the valve I'm going to turn off the light and as the pressure begins to drop we're going to start to see the discharge so let's turn the lights off now now at about 2.7 millimeters and I'm going to turn the pressure down and we'll see what happens keep an eye on the plasma tube 16 15 14 see the beautiful color here this is the color of nitrogen and as the pressure continues to drop you'll notice that the discharge becomes dimmer and dimmer this is not because we're not putting as much power into order we've changed the voltage but we're simply running out of nitrogen ions to produce the light the electrons are invisible all of the light is coming from the the ionized nitrogen and so as we draw it down we produce less species that can actually generate light now another thing is keep in mind is that this looks asymmetrical and the reason it does is because we've put a rectifier in this and so this is the cathode the source of the electrons this is the anode the the final destination for the electrons and so in one respect this is actually a poor-man's linear accelerator 0 to 20 400 volts so a very poor man's linear accelerator nevertheless the electrons are being accelerated toward this end of the tube and ending up at the anode and it's hitting the gas molecules and producing a discharge which effectively at some point disappears because we're not only losing the insulating properties of the gas we're also losing the ions that can conduct the electricity so as the pressure continues to go down we reach a low point for resistance and then the resistance begins to go up again as we remove all of the conductive species a very high vacuum is actually a very good electrical insulator so now what I'm going to do is I'm going to introduce a little bit of nitrogen back into the system so we can take a look at the discharge again so I'm going to crack the needle valve and we're going to add a little bit of nitrogen in here try to get up to a nice pressure not too high not too low now generally most gases will discharge really well between about 100 microns and about 1 millimeter and right now we're running at about 140 microns which is a good number and when you look at this you're gonna see some properties in the discharge tube because of the rectifier and because we've kept the cathode and the anode one end to the other end you can see this asymmetry in the discharge if we didn't use the rectifier stack and we simply sent an AC current in here we would be producing this exact pattern but it would be flipping back and forth 60 times a second and so your eyes wouldn't be able to pick that up so in this case what we have is a very classic discharge the cathode here which is the source of the electrons has a soft glow that occurs around it called the cathode glow those electrons that are being pulled off the tungsten electrode electrode are actually ripping off a little bit of tungsten and that's what's deposited on the glass tube that creates that sputtered dark ring that you see on the inner tube right around the cathode you'll see then what are called the crooks and the Faraday dark spaces that occur here until you get to what's called the positive column also in here you will see a few bands which look a lot like the shock diamonds in a rocket exhaust but they are not shock waves they're actually standing waves that have to do with the nature of the way the light is being produced when the discharge occurs when the electrons strike the nitrogen atoms or the molecules it excites them it actually moves the electrons outward into higher energy states and those energy states are stable metastable meaning they're stable for a few nanoseconds and then they return the energy but unlike say throwing the nitrogen up a slope or up a ramp it's more like throwing the nitrogen up a stairway there's only discrete levels at which the nitrogen is able to accept electrical input and there's only discrete levels as they fall down the stairway that they can return energy in the form of photons the distance of the riser determines the amount of energy in the photon and therefore the amount of color now this would be a nasty stairway because in fact the risers all have different heights and so as a result what we end up having in this discharge is a whole forest of different photon energies different color bands that when all added together produced this overall pink orange hue that you see that's attributable to nitrogen now the other interesting thing that you'll notice is these little striations in the positive column these are due to the fact that as the electrons are moving down and being excited as they move toward the anode they are stimulating some of the nitrogen atoms to give some of the nitrogen to give off light but until they get to a sufficiently high voltage they don't create what's called a cascade effectively the one electron has enough energy to cause the electrons not only to be stimulated in the nitrogen but to rip another electron off of a nitrogen atom that electron can then in turn be accelerated and hit other nitrogen atoms causing them to release additional amounts of light and additional electrons and this cascade creates a a chain reaction that produces a lot more light in these zones here the reason that this does not continue to grow brighter and brighter all the way along the length is because we even though we're accelerating the electrons we're also using up the energy that's being put into them by creating the light by stimulating the nitrogen atoms the striations occur because that product or that that occurrence is not continuous but it's periodic at one of the bright striations we get a lot of cascade and a lot of light and then those electrons that are released are at a somewhat slightly lower energy and so they take a couple of centimeters to build up enough potential to create another cascading event and another cascading event so we tend to get a little periodicity with these striations the striations appear to be stable they don't appear to be moving but in fact they are they're moving very quickly we just can't see it with a slow speed camera which eyes but they appear overall to be standing waves simply because we can't see them moving as quickly as they really do now not only is the stairway that produces the nitrogen kind of a weird stairway and has it produces a whole bunch of different little color bands that we could see if we used a spectrograph or a prism and looked at the different colors but every single gas has a different type of stairway and produces a different forest of individual pure colors that mix to create the hue so what I'm gonna do next is I'm going to change the nitrogen for oxygen and we're gonna see the difference in the color between the different gases so let's go ahead and do that now okay so we've gone ahead and flushed this with a little bit of oxygen now and I'm gonna go ahead and close the valve and let the pressure begin to drop and keep an eye on the discharge tube because in about three or four seconds I think we'll start to see some some color here we go definitely a different color more of a bluish I'm going to turn off this light for just a second on the pressure meter just so you get a better view of the color of the two and if they continue to close this will see the striations begin to develop - as the pressure drops this is oxygen and as the pressure continues to drop the discharge brightness will continue to drop - as we run out of gas this also seems to produce a little bit more noticeable striations each gas has its own pattern and the pattern also depends not only on the diameter of the - of the gas type the pressure the voltage pretty interesting now what I'm gonna do is I'm gonna go ahead and we're gonna try some helium so this is helium it looks a little bit like the nitrogen the band's are relatively similar and a lot less blue than the oxygen but there is a little bit of a difference to that you'll notice and that is that the very light gas seems to have less enough of an effect on the cathode beam that's coming out of the cathode aiming toward the anode and you see what almost looks like a laser beam in the middle and this is the very very light nature of the the helium gas also you'll notice the striations appear at a slightly different location they tend to be a little bit thicker or broader again it's the characteristic of the gas now one of the things that's kind of neat about plasmas is because the electrons are invisible but because the negatively charged positively charged ions will respond to a magnetic field if I take a magnet here and I place it near the plasma I can cause the plasma to do a whole bunch of interesting things I can attract it to the magnet like this and if I reverse the magnet I can push the beam away from the magnet because they're positively charged attract and repel in addition I can do some interesting kinds of shapes you have a lot of fun with what you can do with the magnet and because the field tends to concentrate the ions against the wall you actually get a brighter spot because you're concentrating all the light at that one location and you can also pull the plasma toward you caused it to move away towards you you have a lot of fun with it it's a beautiful thing it's a lot of fun to mess around with and it's exciting when you realize that this is actually at the heart of what is going to be the next revolution in energy production so I hope you found this interesting there's a lot of fun to do and in the next video we're gonna get into magnetic fields we're gonna use some of the equipment on the other side of this table to produce some magnetic fields that can control and move and maneuver the plasma in order to be able to contain it and to be able to manipulate it so hope you found this interesting and if you liked it please give us a thumbs up and give us a comment even if it's something as simple as saying hey that was pretty neat and if you have questions I read all the comments and I try to answer as many questions as possible and if you like the kind of thing that we're doing here on this channel please subscribe hit the bell hit the all notifications and something you might find interesting is that a couple of a weeks ago we produced a video on epoxy and it was pretty well received we got about 40,000 views within the first day but we noticed on our analytics that out of those 40,000 views only 3000 of them had been from people who are notified in other words our subscribers we have over 350 thousand subscribers and so kind of interesting that only less than 1% of the people who saw that video did so because they were notified clearly YouTube is not doing that much to try to notify people who subscribe to a channel because the content is interesting to them in addition we've also had comments from people who thought they were subscribing and had been involuntarily removed so if you do think the troops have thrived take a few seconds and make sure that you still are because it helps us in terms of growing the channel and even more importantly let people know what we're doing here tell co-workers and students and teachers and family members and anybody else who might be interested in what we're doing helps us to grow the channel and helps to offset the cost of what we're we're trying to accomplish here in any case I want to thank you very much for watching stay safe with the one hand rule I wish you a good evening you take care [Music] you

Channel: Tech Ingredients

Views: 349,047

Rating: 4.9682727 out of 5

Keywords: Plasma, Fusion, Vacuum, Vacuum tubes, High voltage, Transformer, Rectifier, Argon, Oxygen, Nitrogen

Id: zcpDGKH9_SE

Length: 50min 37sec (3037 seconds)

Published: Sat May 02 2020