Move over Fusors, here come the Cyclotrons!

[George Schmermund]

Nothing new here, but it's good to see that they're starting to organize.

http://www.symmetrymagazine.org/pdfs/20 ... lotron.pdf

[Richard Hull]

I see our fellow fusioneer and Neutron club member Raymond Jimenez attended this small conference. It is little ad hoc conferences like this, organized by a single or a couple of "spark plug" types, that make for the beginnings of a future permanent yearly gathering like Teslathons and HEAS conferences.

Cyclotrons that are actually useful for amateur experiments have more serious issues with x-radiation than fusors. They have the advantage of not requiring any expensive gases unless you plan on deuteron beams. Then there is that magnet thingy...... This is the thing that would stop all but the most adventurous builders. Still, there are possibilities with modern super Nd:Fe:B magnets set in a medium sized yoke. The fields have to be rather unifrom over the entire chamber.

The thought of building these and never putting them throught their maximum operational paces or experimenting with them would be abhorant to me, but according to the paper, apparently this is sometimes the case.

The bit about cyclotron building changing the lives of thsoe involved could be said of fusor construction as well. Lotsa' tech stuff involved along with all the usual dangers, gotcha's and cash outflow issues.

Richard Hull

[Chris Bradley]

Can someone help me understand the caption to the picture on p 27? It says "Ions in the Rutgers cyclotron spiral down during a test run.". I can see a few blurs of what look like glow plasmas. I wasn't aware that one could see ions within a cyclotron spiral.

[Richard Hull]

I wish I new more about this stuff.... The cyclotron is a much deeper vacuum than a fusor, (need for long MFP). However, I assume they are injecting a gas and even at lower pressures, within an intense magnetic field, you can get the glow as seen in discharge tubes due to the spiraling accelerated particles within it. This is how the penning gauge works down to 10e-6 torr.

Richard Hull

[George Schmermund]

Chris - check out pages 32 & 33.

http://www.cyclotronconference.org/pres ... hton_3.pdf

[Chris Bradley]

hmmm.... not entirely convinced. I think it is an assumption that the blue trails are 'ions' (or ion trails).

I get some odd electron/plasma 'spirals' in my experiment sometimes, for which the best explanation I have come up with is that escaping ions crash into structures, some sort of charging occurs and electrons get displaced. I say this because it is always on the 'anti-clockwise-side' of the structures (which is the direction the ions would be going). In such cases you also see these spiralling blue trails. (If you crank up the drive voltages, you can get these 'charged-up' regions to get sufficiently high that they break down into discharges to the nearest ground structures.)

For reasons I can only speculate on, these spirals typically do not form up in the plane orthogonal to the magnetic fields.

[Raymond Jimenez]

I believe the spirals coincide with the ion paths, probably the effect that Richard hinted on that causes the glowing. It's probably recombination in the path of a slow-moving beam, since the vacuum isn't perfect (though don't hold me to that). They are operated at much deeper vacuums (as deep as possible, ideally).

The spiraling downward was an unintended effect of vertical asymmetries in their ion source, which resulted in an initial kick down---and since there's not a large restoring force, the particles keep on headed down, crashing into the chamber walls.

The conference was pretty fun; I gave a small brief about my synchrotron project (which is still slowly going, due to research/schoolwork), and most of the people there were DIYers just like us. Small but quite a nice community, made up of people who just want to do work and get some real practical data.

Raymond J

[Chris Bradley]

Recombination between electrons and ions? Of course it is - we can see that - but why are there electrons there to recombine with, if extra ions aren't being generated? And if they are then why does the cyclotron motion not pick those up and also accelerate those into a visible 'cloud' around this blue trail?

I thought cyclotrons are dead-inefficient *because* all those extra ions being produced by background-scattering/ionisation get uselessly accelerated in spirals not centred about the main ion-generator? You still can't see them, in a normal cyclotron.

OK, let me ask a different question, assuming that I am simply misunderstanding what I am looking at; why does the picture in the lower LHS of slide 29/42 look so different to the slide of 32/42?

[Raymond Jimenez]

Ah, sorry for the misunderstanding. I can answer at least one of these.

The reason cyclotron motion doesn't pick up the rest of the ions is because their path doesn't cross the RF gap. Seems likely to me that the parasitic ions don't get enough speed for their paths to get big enough to cross the gap, so it's not a problem. Additionally, the gap only accelerates in one axis, so if their gyrocenter isn't coincident with the chamber (which it's pretty much guaranteed, since they're not generated at the center of the chamber), they won't get a full kick, if any. I haven't heard anything about cyclotrons being dead inefficient, so much as they're not useful at higher energies due to relativistic effects. I'd imagine that most of the inefficiencies come from resistive RF losses/coupling problems and not inadvertent ion acceleration. Might be wrong though.

Not sure where the ions are going when they recombine, actually. Hadn't thought about that.

In slide 29, there is one working aperture. As they note, there's a kick downward, but it's fixed by the weak focusing force caused by the field gradient (slight weakening of the field as you go outward). To fix this problem, they tried to remake the chimney and install pullers--the result being on 32. My assumption is that the kick imparted by the installed pullers was too much for the weak focusing to correct, thus just resulting in beam loss.

[DaveC]

George -

Thanks for posting that link. Very interesting to read about these folks. I was wondering if the young man Peter Heuer was a relative of Rolf Heuer who is/was the LHC project director at CERN.

Dave Cooper

[lutzhoffman]

Very interesting and informative post, I however seriously doubt that this will ever catch on for two main reasons:

1. The extreme weight and size of the component parts: We are talking over a ton, for only 1 MEV protons. Due to their higher atomic weight D+ ions will only attain 1/2 of the final energy of protons in any cyclotron. Thus a device with over a ton in mass, with KW level RF systems, will only give you 500 KEV D+, at micro amp power levels.

2. Extreme low efficiency: Just to run the magnet for even a small 1 MEV proton cyclotron, requires about 10KW+ of electricity, now add the RF, and a huge capacity vacuum system, and I am willing to bet that you are looking at about 20KW of power just to get a few micro amps of 500-600 KEV D+ ions. Even this may require an upgrade to your home power delivery, and a even a second job just to pay the electric bill.

Now compare this scenario to a simple old fashioned high voltage DC linac: 500KEV D+ ions, can be done without a pressure tank, with simple air insulation. All this in a rig which is only about 2 meters tall. The power source can even be a simple Van De Graff generator for the several micro-amp power levels that we are talking about. The total system power draw would be about 1KW here, including the vacuum system. For more power a voltage multiplier could be used, but then you would need a concrete cave for radiation protection, which is out of the budget for most folks who do not happen to have a handy limestone cave, old mine, or lava tube on their home lot.

If this is not "techi" enough for you then a RFQ linac could also be a superior option to a cyclotron as well: With modern CNC machining the 4 vanes could be done with a reasonable effort, now add the RF tank, and an RF power supply which is on the same level as the one required for a cyclotron. Then throw in a dash of math, and some luck, and bingo you have the same thing as a 10 ton cyclotron. I am sure that a determined fellow with the knowledge level required, like Carl, could pull this one off. ( I do not know Carl personally, but I have read enough of his material to really feel that he capable of doing this one, if he really wanted to, as are some others who contribute)

So to close I feel that the cyclotron is very fascinating, and realistic, but only in the form of the very small incarnation. Something like the totally cool mini-cyclotrons that are being built by some folks on this forum. But the idea of many folks building large high power units is simply not realistic for anyone who does not happen to have, some totally unique set of resources, parts, and knowledge, all at the same time. For most folks a fusor is much better, and a fusor will never upset the community like a cyclotron in the basement will, remember Alaska?

The fusor has an impeccable track record for simplicity, safety, and for ease of use, which may be in part why it warrants having its very own forum. Fascinating reading none the less, but I think that the large cyclotron, will never become prominent in amateur circles, unless superconducting magnets saturate ebay or something like this. It was fun to read and dream about though : )

[Richard Hull]

I would imagine that cyclotrons will not rival the fusor in individual amateur appeal. The cyclotron is a "bridge too far" for virtually anyone without deep pockets and a lot of "on hand" skill sets.

Still, it would be the ultimate coup for a lone builder. It would appear as a much more "doable" adventure for an advanced group of older amateurs or undergrads.

Richard Hull

[Dustin]

It would also be cool to investigate this device for fusion possibilities.
Simple modification of the structure allows for colliding beams within the realms
of permanent magnets to get to fusion energies with pretty good confinements.
I was surprised I could find no such devices already being investigated.
Steve
(forgive my crude sketch)

[Chris Bradley]

The reason for no such investigations; scattering losses. The cyclotron cannot recover the energy of the majority of ions that will scatter or miss, even if it was possible to achieve good enough alignment.

If a beam-beam attempt, without scattering energy recovery, was desired, would it not be easier to just have two ion guns facing each other, because fusible energies can be reached in a single accelerator stage?

[Dustin]

I disagree.
In high vacuum conditions the ion will keep circling until it collides or gains enough energy to run off the edge. This may give it thousands of opportunities to collide /fuse or scatter and be lost.
Two ion guns, you only have one passing shot and the energy is lost regardless.
I think its a neat idea and not too far astray from what you are doing.
Unfortunately its quite a task to build one of these monsters.
Steve

[Chris Bradley]

Steven Hosemans wrote:
> I disagree.
> In high vacuum conditions the ion will keep circling until it collides or gains enough energy to run off the edge. This may give it thousands of opportunities to collide /fuse or scatter and be lost.

Sorry, Steve, I don't understand what you are getting at.

It may have thousands of opportunities to collide with the background medium (just like a fusor) but why would it have thousands of opportunities to collide with the other spiralling beam at some particular gyroradius? If it were to miss its one opportunity then it'll be off into the chamber wall, and if it does get its one opportunity, then how does that differ straight beam-beam? Even if each ion did get a guaranteed head-to-head with another ion, it's still due to scatter with a considerably higher probability that for it to fuse.

The basic configuration of a cyclotron does not form a closed orbit beam focus at a given gyroradius for scattered ions to recover back to after scattering. Instead an ion hops through a sequence of different half-circle radii at it 'collects' more energy from the e-fields each time it passes the edge of a dee.

[Dan Tibbets]

Ditto for what CB said (is that possible?)
Two colliding beams with one chance interception might be useful for getting fusion or other atom smashing reactions to occur in one spot (which would make subsequent measurements more convenient), but this concentrated meeting point would also promote proportionatly more coumlomb scattering collisions and subsequent loss, unless there is some recovery process like that in a gridded Fusor, or vertually gridded fusor (like Polywell). Even then, the possibility of net gain fusion is very uncertain (debated) even with perhaps hundreds of thousands, if not millions of recirculating chances with modest energy expenditures.
The Polywell supposedly has a central density advantage of perhaps several thousand (or more) over Tokamaks, and still needs this recirculating magnitude to have a chance. I guess that a Tokamak would require thousands of more recirculating passes (confinement time) to break even due to the smaller effective density. I'm guessing FRC devices are intermediate between the Tokamak and and Polywell. I'm not sure where in this scheme a high Beta Tokamak (or other torus type machine) would fall.

The exception to this requirement for many recirculations outside a reactive core or focus is in inertial confinement where the density is so great that at the center, there are so many collisions in such a small volume and short time frame, before the dense cloud disperses (blows up), that a large portion of the ions fuse. There are still very many coulomb collisions for each fusion collision, but the mean free path is so short that this many chance in one pass senario applies to this very dense situation.
I suppose that two intercepting particle beams might reach this 'super dense' condition in a tiny volume, but the density (energy) of the beams would have to be ridiculously high, as you are converging two tight beams as opposed to an effective three dimensional collapse of a sphere.

Dan Tibbets

[Dustin]

I agree with several points you make.
There is no method to recover from a scattering event and all scatterers will be lost.
It is not a closed orbit but the progressive increase in orbit radius is a function of RF amplitude so this would determine the the number of passes or opportunities to fuse / scatter in the intersection of the circular 'venn diagram' so to speak before exiting the outer radii.

Unlike two focused ion beams to a point, where the space charge approaches applied voltage,reducing ion energies below kinetic energies required for fusion, the space charge at the intersection (in the duo cyclotron) is only twice the beam space charge.

At the intersection, all of the ions have close to the same amount of kinetic energy, where in linear colliding beams the energies of the ions can have a large range of energies (as some scatterers are recovered and some neutrals are ionised in the potential well, well below the applied voltage.
Perhaps I'm rambling but to me it seems an attractive alternative and possibly another method that will never make unity.
Steve.