Giant rotary capacitor - Page 1
Forum section: electronics / general

author: daqq
author_rank: Super Contributor
timestamp: October 26, 2018, 05:16:04 pm
content: From the CERN facebook page:Quotehttps://www.facebook.com/CERNLibrary/photos/a.10150908032326970/10156527944126970/?type=3&theater

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 26, 2018, 06:21:49 pm
content: Looks more like a turbine or jet engine than a capacitor.

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 26, 2018, 06:52:17 pm
content: Why does it need to spin?

author: Benta
author_rank: Super Contributor
timestamp: October 26, 2018, 07:14:59 pm
content: Quote from: Cyberdragon on October 26, 2018, 06:52:17 pmIt doesn't. The rotor will be turned a few degrees to change the capacitance between the plates.But there's some terminology mixup here. It should be called a rotary capacitor, not condenser.A rotary condenser is a synchronous motor, where excitation is varied to compensate for bad power factor. Used in 50/60 Hz power distribution networks. Not relevant to this.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 26, 2018, 07:35:01 pm
content: The capacitor spins to synchronously modulate the accelerating RF frequency as the particles speed up:Quotehttps://indico.cern.ch/event/286275/contributions/651650/attachments/531390/732777/Part-4.pdf, slide 6There's more info on the CERN Synchrocyclotron RF system in this document:https://cds.cern.ch/record/135601/files/abc-01.pdfFor more info on the techonology, the keywords to search for are "Synchrocyclotron ROTCO"

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 26, 2018, 07:38:34 pm
content: The stator shape is really weird, and it doesn't make sense how it would connect into anything else; is it just wired to the beamline? -- in which case, why does it need to be so beefy? Or does the beamline go through it, somehow, in which case why is the axis solid?The beefiness suggests high speed, if nothing else.I wonder if the stator shape has to do with the transition from cyclotron to synchrotron resonance? -- as velocity increases into the relativistic regime, the relationship between frequency and energy changes, and a tuning component like this could be used to keep it in sync. The stator would then be cut to get just the right frequency as the particles speed up, and maybe it's stepped to keep particles confined on a desired orbit, or maybe the magnets vary in a complementary way. It would be repeating quickly, because particles are injected from a smaller cyclotron, accelerated to relativistic energies here, then accelerated further in the main beamline (or a third one before the main, I forget), and the time taken is nearly light speed around a modest sized chamber or beamline: modestly fast for electronics, but bleedingly fast for mechanics!Tim(Ed: I took my time, typing that while distracted, so I didn't see the above posts before sending. It looks like at least some of my suspicions were correct.)

author: RoGeorge
author_rank: Super Contributor
timestamp: October 26, 2018, 07:45:22 pm
content: Why is the older dude dressed as a bride?

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: October 26, 2018, 08:07:34 pm
content: Quote from: Benta on October 26, 2018, 07:14:59 pmThe terms condenser and capacitor are synonymous. 'Condenser' dates from Leyden jar days when they though the jar condensed some kind of ethereal fluid, bit like condensing moonshine. Interestingly, it was awhile before they realised that it was not the jar as a container, but the dielectric of the glass which provided the storage. When someone tried lining the jar with foil, that made it far more effective. BTW be careful experimenting with Leyden jars, they might look crude but they can store a dangerous amount of charge.The term was replaced by 'capacitor' mid-20thC simply because that is a better description of its function. As often happens, the older term remained in use for a very long time.BTW it rotates to distribute the flux evenly. Otherwise parts of your DeLorean might end up in different eras. Which could be bad.

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 26, 2018, 08:11:37 pm
content: I found another good document on the rotating condenser and its operation:https://indico.cern.ch/event/572852/sessions/239010/attachments/1487020/2309693/600MeV_SC_Foundation.pdfThe relevant part starts on page 27; "The Rotary Capacitor: Tuning Acceleration"Edit: This paperhttps://accelconf.web.cern.ch/accelconf/p71/PDF/PAC1971_0307.PDFcontains some interesting electrical parameters. The capacitance of the Rotco sweeps between 5 nF and 400 pF, giving an operating frequency of 30 MHz at particle injection, sweeping down to 16.5 MHz for extraction 1383 µS later. The full RF circuit including additional tuning capacitors is given in the second link in my previous post.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 26, 2018, 08:34:35 pm
content: Quote from: RoGeorge on October 26, 2018, 07:45:22 pmThat is very gender-identity insensitive on your part.Or perhaps management only has to wear lab-coats while the actual worker-bees have to wear clean overalls/jumpsuits.

author: amyk
author_rank: Super Contributor
timestamp: October 27, 2018, 02:22:54 am
content: It reminds me a bit of thehttps://en.wikipedia.org/wiki/Alexanderson_alternator

author: Hypernova
author_rank: Unknown
timestamp: October 27, 2018, 04:00:59 pm
content: Quote from: IanMacdonald on October 26, 2018, 08:07:34 pmTo this day the Japanese word for capacitor is 'condenser' written in katakana. I did know that until I saw a whole box of Nichicons I took delivery of. Thiswiki pagehas a pretty complete list of languages that continue to use the term.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: October 27, 2018, 04:18:27 pm
content: Also in German, a capacitor is a "Kondensator" which also comes from Latin "condensare", so it literally means "condenser". In today's words, you could say electrons are (or generally speaking charge is) condensed.

author: amyk
author_rank: Super Contributor
timestamp: October 27, 2018, 05:35:31 pm
content: Quote from: Hypernova on October 27, 2018, 04:00:59 pmThat's what the "con" part of the name is... notice how a lot of the Japanese capacitor manufacturers have that in their name.

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 28, 2018, 12:56:10 am
content: Skookum as frig. Basically the same concept used in older radios to tune the frequency I imagine? It's changing the surface area of the plates which varies the capacitance. Except this one is probably build to ridiculously tight tolerances. You sneeze in the same room and it probably needs to be re-calibrated. By virgin gray beards of course.

author: daqq
author_rank: Super Contributor
timestamp: October 28, 2018, 07:32:56 am
content: A bit off topic:Assuming DC, and conservation of energy, if you charge a variable capacitance capacitor at, say, 5nF to, say, 100V, then change the capacitance to 1nF, will there be an increase in voltage (to around 220V), or will the energy move some place else?

author: daqq
author_rank: Super Contributor
timestamp: October 28, 2018, 08:15:32 am
content: QuoteThanks... But E=0.5*C*U^2 ? With 500V @ 1nF the energy would be 5 times as high.100V @ 5nF = 25 uJ500V @ 1nF = 125 uJIt should be around 223V @ 1nF = 25 uJ to keep the energy the same.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 28, 2018, 08:56:52 am
content: I deleted my previous message you just quoted. Anyway, the setup I was talking about was different from what you are asking (also, I introduced some mistakes with my many edits and additions).

author: Wolfram
author_rank: Frequent Contributor
timestamp: October 28, 2018, 01:44:35 pm
content: Quote from: daqq on October 28, 2018, 07:32:56 amDue to conservation of charge, the voltage will increase to 500 V if you reduce the capacitance to 1 nF. The additional energy stored in the capacitor will have come from the work of separating the plates against the electrostatic force of the field between them.

author: Red Squirrel
author_rank: Super Contributor
timestamp: October 29, 2018, 05:44:18 am
content: That's interesting, never would have considered that the voltage would change. Would be interesting to use that concept to build a boost converter. There's better ways of doing that such as using mosfets and inductors, but could be fun and have a "steampunk" aspect.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 29, 2018, 05:59:22 am
content: I mean, Wimshurst machines areverysteampunk, and they exist already, so that's fun.Tim

author: RoGeorge
author_rank: Super Contributor
timestamp: October 29, 2018, 06:00:18 am
content: There are already many types of electrostatic voltage multiplier machines. Here is the first video returned by a searchThe main phenomena is based on Charge Conservation, not Energy Conservation (the experiment proposed bydaqqis different - wants to keep energy constant while varying capacitance, so in order to do that it will also be necessary to remove just the right amount of charges from the capacitor's plates while changing its capacitance - not impossible but a rather odd setup IMO). If we go for the usual setup, where the charges are kept on the plates while varying the capacitance, then mechanical energy is transform in electrical energy by the device.

author: TerraHertz
author_rank: Super Contributor
timestamp: October 30, 2018, 08:07:08 am
content: This is all very interesting. Though if someone walked me up to that machine and asked me to put my hand in through the blades, I'd say no. And other things not fit for printing here.That question of "put opposite charges on two plates, then move them further apart, what happens to the voltage between them?" has intrigued me too.I think it's a bit misleading as stated. With the initial placement, if there's a field of 1 volt/meter, and then you increase the gap, the field strength goes down. There's still the same amount of charge on the plates, and that charge separation is the only thing that remains constant. Moving them apart does work, but it didn't change the amount of charge separation (Q). What increases is the potential energy of the system, ie how much energy you'd get back by allowing the charges to recombine.The 'voltage' you are thinking of as the result of current flow through a resistance, or created by some mechanical/chemical process that can maintain the voltage even when there is current drain. With the plates example that's not the case. There's no current flow, and if there was you are discharging the cap's charge separation, causing the electric field to collapse, and recovering the potential energy.V = Q/C. Here V is a measure of potential energy available. Note it doesn't increase linearly with separation, as C doesn't diminish linearly with separation. Anyone know or can derive the equation for the limit approached as plate separation goes to infinity?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 30, 2018, 09:45:39 am
content: Quote from: TerraHertz on October 30, 2018, 08:07:08 amThe field strength remains constant, assuming orthogonal geometry with no fringing (e.g., infinite plates).I went through the ratios a few days ago, feel free to check it out (although "a few days" for me probably means pages of replies to sift through, sorry).Tim

author: RoGeorge
author_rank: Super Contributor
timestamp: October 30, 2018, 11:50:29 am
content: Quote from: Red Squirrel on October 29, 2018, 05:44:18 amSeeing is believingAt minute 06:05, he slightly lifted the can lid from the bottom of the can, in order to form a capacitor between the lid and the body of the can. Then, he applies 1.5V on the lid (by shortly touching the lid with the "+" terminal of the AAA battery, the "-" terminal of the battery is wired to the body of the can). Then, he lifted the lid even more. Note on the voltmeter on the right side how the voltage raises very rapidly with the lift, going out of range of the analogue indicator.