Giant rotary capacitor

[daqq]

From the CERN facebook page:

This picture shows the first of two rotary condensers for the radio-frequency system of the Synchrocyclotron. It was transported to CERN in June 1973 while a second (spare) condenser was being completed in Berlin. In the picture the clearances between the radial rotor blades and the specially shaped stator blades mounted on the circumference of the housing were being checked.

https://www.facebook.com/CERNLibrary/photos/a.10150908032326970/10156527944126970/?type=3&theater

[Richard Crowley]

Looks more like a turbine or jet engine than a capacitor.

[Cyberdragon]

Why does it need to spin?

[Benta]

Why does it need to spin?

It 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.

[Wolfram]

The capacitor spins to synchronously modulate the accelerating RF frequency as the particles speed up:

A Synchrocyclotron is a circular accelerator in which the frequency of the accelerating electric field is modulated in order to compensate the decreasing period of revolution of the particles. This decrease is due to the relativistic mass increase and the decreasing field during acceleration.

https://indico.cern.ch/event/286275/contributions/651650/attachments/531390/732777/Part-4.pdf , slide 6

There's more info on the CERN Synchrocyclotron RF system in this document: https://cds.cern.ch/record/135601/files/abc-01.pdf

For more info on the techonology, the keywords to search for are "Synchrocyclotron ROTCO"

[T3sl4co1l]

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.)

[RoGeorge]

Why is the older dude dressed as a bride? 

[IanMacdonald]

  But there's some terminology mixup here. It should be called a rotary capacitor, not condenser.

The 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. 

[Wolfram]

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.pdf

The relevant part starts on page 27; "The Rotary Capacitor: Tuning Acceleration"

Edit: This paper https://accelconf.web.cern.ch/accelconf/p71/PDF/PAC1971_0307.PDF contains 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.

[Richard Crowley]

Why is the older dude dressed as a bride? 

That 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.

[amyk]

It reminds me a bit of the https://en.wikipedia.org/wiki/Alexanderson_alternator

[Hypernova]

  But there's some terminology mixup here. It should be called a rotary capacitor, not condenser.

The 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. 

To 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. This wiki page has a pretty complete list of languages that continue to use the term.

[0xdeadbeef]

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.

[amyk]

To 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.

That's what the "con" part of the name is... notice how a lot of the Japanese capacitor manufacturers have that in their name.

[Red Squirrel]

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.

[daqq]

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?

[daqq]

C=Q/V by definition. Since the electric charge doesn't leave the capacitor's plates, the voltage will increase to 500V.

Thanks... But E=0.5*C*U^2 ? With 500V @ 1nF the energy would be 5 times as high.

100V @ 5nF = 25 uJ
500V @ 1nF = 125 uJ

It should be around 223V @ 1nF = 25 uJ to keep the energy the same.

[RoGeorge]

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).

[Wolfram]

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?

Due 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.

[Red Squirrel]

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. 

[T3sl4co1l]

I mean, Wimshurst machines are very steampunk, and they exist already, so that's fun.

Tim

[RoGeorge]

There are already many types of electrostatic voltage multiplier machines. Here is the first video returned by a search



The main phenomena is based on Charge Conservation, not Energy Conservation (the experiment proposed by daqq is 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.

[TerraHertz]

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?

[T3sl4co1l]

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.

The 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

[RoGeorge]

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. 

Seeing is believing

At 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.