does a electron beam attract? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 06:02:23 pm
content: If you have emission in a vacuum, is there any mechanical forces on the beam?For instance, if you built a vacuum tube on very low friction swing arms (jewel bearing) would the arms pivot from the beam?I.e. a traditional vacuum tube is placed horizontally with all elements aligned correctly. Once you turn it on does anything move?

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 06:05:51 pm
content: An electron beam has momentum. So it will produce a reaction force at the emitter. (Albeit, an immeasurably tiny force.)

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 06:14:51 pm
content: so the two pendulum arm would move away from each other by some small amount in addition to getting hot? just like a garden hose

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 06:20:48 pm
content: A vacuum tube itself doesn't experience any forces since it is a sealed glass envelope.But if you somehow builtinside a vacuum chamber, a rotating pivoting arm like a Crookes radiometer, and if you somehow managed to put beam emitters pointing sideways at each end of the arm, then it could rotate due to the reaction force of the beams. But I don't know how such a device could be constructed. There are too many big, heavy, power-consuming and complex parts to suspend on the ends of the arms.The idea is similar in concept to the idea of ion thrusters as rocket motors.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 06:24:26 pm
content: I would imagine the best place to build this is in a space station that has a room where you can open a windowI thought ion thrusters use a gas though ,like a plasma cutter. So this would just be a electron thruster, which is the same but much weaker ? So the electrons are propellant instead of argon.This has nothing to do with the tube vaporizing, I know it slowly vaporizes, and that probobly makes it 'ion thruster' like, but I imagine you could make it so only the electrons get off the electrode

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 06:28:11 pm
content: If you continually shoot ions or electrons out into space, then you are going to start building up a static charge. Probably not a good thing in the long run.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 06:48:11 pm
content: I mean a closed circuit so the electrons are all captured by the other electrodeit sounds like basically it would react like a angle gauge

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 07:15:29 pm
content: If you capture the electrons you also capture the momentum, meaning that no net thrust is generated.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 07:30:41 pm
content: I am not sure I understand.If I attached a garden hose, a plate and a recirculating pump between two pendalums, I expect that when you turn the pump on, the garden hose recoils, the plate that gets hit by the water also recoils, and the water to drip into basins under each connected to a pump and be circulated OK to keep the system running.So the angle between the two pendulums would be proportional to the water flow

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 07:45:49 pm
content: That's a very complicated way to generate an angle between two pendulums. What purpose would it serve?

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 07:48:52 pm
content: It seems conceptually the same as suspending vacuum tube parts where the emissions is water, and it seems like a closed system

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 07:53:39 pm
content: like this, do the arms move away from each other, if you figure out the mechanical design. If you turn it on and off would it sway?

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 07:54:55 pm
content: Yes, you could in principle generate a static force between an emitter and a receiver by sending an electron beam between them. However, the force due to beam momentum would be immeasurably small compared to the force generated by any electrostatic field due to the potential difference between two such arms. In a typical experiment, electrostatic fields would overwhelm other forces so completely that they would be impossible to measure.So, it is still hard to understand the point of the question?

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 07:56:17 pm
content: that means you need some kind of electrostatic force nulling system.It sounds like you could measure the angle and it would be related to electrons by some small amountthen you can have a angle meter with angle proportional to voltage/current

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 07:56:51 pm
content: Quote from: coppercone2 on August 17, 2024, 07:53:39 pmYou have anode positive, cathode negative. Unlike charges attract. So the two arms would be attracted together.

author: IanB
author_rank: Super Contributor
timestamp: August 17, 2024, 07:57:53 pm
content: Quote from: coppercone2 on August 17, 2024, 07:56:17 pmSee: "impossible to measure" above.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 07:58:32 pm
content: that is interesting because if one day someone managed to build it, they can have a kind of reverse fuse, it should touch and fuse together.I say impossible for the next 10000 yearsyou could probobly get this through the patent office no problem

author: SteveThackery
author_rank: Super Contributor
timestamp: August 17, 2024, 08:15:28 pm
content: What exactly are you patenting? I haven't understood what problem you are trying to overcome, or what functionality you want it to provide. Sorry if I'm being thick.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2024, 08:25:51 pm
content: I want to understand what electron beam parameters are and what it theoretically does in different situationsfor instance now I know it might have some force that is very difficult to measure at this point in time, meaning it is not a design concern.I am sure its weird to other people that get this idea that its a 'stream' hitting something, so naturally you think it might make something moveother fun activities might be using laser clamps to drop a nano particle into a thermionic beam, then its like the physics problem of swimming across a river. Or boats that go down a "stream" like in a CRT

author: ejeffrey
author_rank: Super Contributor
timestamp: August 17, 2024, 09:42:20 pm
content: Then the answer is yes. Electrons have momentum. A beam of electronics hitting a target will knock it back ever so slightly.However, electrons have about 1/2000th the mass of a proton, so in ordinary neutrally charged matter the momentum of the electrons is an insignificant contribution to the total. And if charge neutrality isn't maintained, the elecrostatic forces will outweight any impact force.Ion thrusters tend to use heavy elements for this purpose, such as xenon or krypton. Also ion thrusters actually emit neutral atoms. If they didn't, the space craft would quickly charge up. The atoms are ionized, accelerated through an acceleration potential, then recombined with electrons before exiting the craft to produce high velocity neutral atoms. since the electron mass is insignificant compared to the ion mass, the recombination doesn't slow the ion down hardly at all.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 17, 2024, 09:47:42 pm
content: No, or not really.https://www.google.com/search?q=%281mA+%2F+elementary+charge%29+*+sqrt%282+*+9.1093837e-31+kilograms+*+100+electron+volts%29I *think* that's right... the number of electrons, times the momentum of an electron at that energy. Taking 1mA and 100V as very typical values.IIRC, µN are just measurable, maybe nN for small things, but you'll have a hard time making mA in things that small, so, it seems unlikely. Meanwhile the electric field is huge:https://www.google.com/search?q=%28%28100V%2Fmm%29%5E2+*+electric+constant+%2F+2%29+*+1cm%5E2The field could be balanced by placing symmetrical electrodes while having asymmetrical electron flow, but are you really going to balance that to within a percent,while the balance is moving?It'll just unbalance, swing around and short out.Well, motion is manageable: one would employ a differential field plate/set, and control arm motion based on laser reflection, servoing it stationary. This also removes the spring-mass complex pole, allowing the control loop to assert a lower mechanical impedance, faster control, and doing the test at different frequencies may allow separation of interfering effects like adsorption and expansion.An electron beam welder might be more promising: currents are comparable, but the energy is much higher (10s keV). But as the name suggests, this is likely to melt the target, so, that's a bit of a non-starter.Note also, everything in here is going to be hot, and is surrounded by just a little bit of gas -- heat means emission of adsorbed and chemically-bound gases, and convection of what remains in the chamber. That too will dominate the errors.Making the EBW plate as an electric "catcher" (have an outer grid (ring, or tube, more like) set to ground potential, inner plate set to -V), might have some merit -- most energy gets recycled into electric current, rather than dissipated as heat, and only two connections up the torsion filament are needed, versus 3+ for a heated cathode with grid. Albeit at high voltage (the insulation up the torsion filament might be worse than using thicker wires for heater power, lol).Tim

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 22, 2024, 09:07:45 am
content: The rest mass of an electron is about 1/1800 of that of a proton, and protons and neutrons pretty much have the same weight.Atomic number of copper is 29, and that makes the mass ratio 58 times worse. The forces caused by the movement of an electron are also independent of the medium it moves in. Movement through a copper wire would exert the same forces as through a vacuum, so you would also have to account for the electrons flowing though the wire into the vacuum tube.But on top of all that, the drift speed caused by current though a wire is pretty low. If you want to do a fun calculation, then calculate the amount of electrons passing though a given point in a wire if it has a current of 1A. (It's a big number). And then divide that by the number of atoms in the cross section of the wire (just take a simple and realistic 1 square mm). This is also a big number. The result is the (average) speed of the electrons, and this is a (very likely surprisingly) small number.The actual speed of electrons (with which it's whizzing around the nucleus) and movement (vibration) due to temperature are all very much bigger. I'm not sure if it would be correct to state that an electron (on itself) has brownian motion.The electromagnetic forces caused by the movement of the electrons is also very much bigger then the mechanical forces due to movement of the electrons. All these things combined, it's a nice brain exercise, but of no practical value.If you start reading in that direction you'll discover that the mass of things like neutrons, protons and electrons is not constant. If you go deeper into that, it all gets really weird (but interesting), so consider yourself warned.