Talk-Polywell.org

MSimon wrote:

chrismb wrote:

MSimon wrote:chris,

Other than the mass difference why should ions vs electrons matter?

Some times you seem so perceptive and other times you seem thicker than a brick. It is like two different people using your name.

The difference isn;t the issue, the mix is. Magentrons have no ions in them, just a load of space-charge inducing electrons. This is something quite different to a thyratron with a 'quasi-neutral' mix of ions and electrons undergoing a discharge event.

But is it a "real" discharge event? The current is limited by well formation.

And well formation says that there may be a series of layers of alternating separated charges.

Of course with no data to go on you could be right. OTOH we have the Navy puttying up significant money so the odds are that something so fundamental is not a problem.

This is a potentially large topic and one which I have a particular interest in thinking more on. So I've moved it over from the other thread. Please share in my thinking-out-loud here:

Most controlled fusion attempts to date are by some form of plasma discharge, which seems very very wasteful to me as what ends up happening is that the electrons suck up all the energy for themselves (greedy little blighters!) then radiate it indulgently whilst they play amongst themselves. Chucking a big current through a gas/plasma can certainly accelerate particles within it but they are poorly directed and thermalise essentially instantly, so you've gotta heat the whole lot up in one go as you can't get the energy into a targeted number of particles. Not wanting to draw too strong a conclusion, but it is of no surprise to my thinking that the only known over-unity fusion reactions (natural or man-made) do not involve electrical discharges.

It is also, then, of no surprise in this line of thinking that the way forward needed with Tokamak is to remove the dependency on the toroidal current. The approach is to cause to generate so called 'banana' orbits that will use thermal motion to generate the necessary particle currents, i.e., that will mean it is no longer a discharge device (by virtue of it being simply the 'shorted secondary' of a huge transformer).

(In that context, perhaps the stellarators (that do not depend on that induction current) have an immediate advantage over tokamkas, but simply they've been too complex to build until more powerful computers have been able to help design the required magnetic coils. Nonetheless, I think the biggest SC version of this, LHD, has maintained a fusion-type plasma for the longest period so far.)

So we turn to Polywell; will it run as a discharge device, or will it act as something else? There are other types of ion generating devices that do not rely on electrical discharge and produce and retain ions in the, arguably, most efficient way possible. These are crossed-field devices like the Penning trap, the Hall effect thruster and 'anode layer' ion source, all of which work in very similar ways. They have no such losses as discharge devices and might theoretically draw no current whatsoever to maintain what is then a non-neutral population of particles (were ions and electrons not prone to gyro-orbit hop across the magnetic field).

Sound similar to Polywell? It does have commonality with some of the features of these devices, but I also can see the potential for a large amount of discharge current being pulled by the device (through the electron guns) because it is not a well-defined ExB volume, only that it is so in the uniform bits away from the cusps, as evidenced by the well-discussed electron losses.

So I'm thinking that I generally judge a fusion device by its input current, as a first-pass towards considering any viability. How much external discharge current does the Sun pull – none, so it's 'got a chance of working' (!). How much external discharge current does an H-bomb pull – none, so 'that might work' as well!! How much does a tokamak draw – multi mega-amps. How much does a fusor draw – 10's mA, but that's quite a bit considering the relatively small population of ions it actually gets, and keeps, moving.

How much does the Polywell suck up? This will be one measure I judge it by.

So in reply to MSimon, I agree it will not be an all-out discharge device, but nor will it be of the quality of efficiency of a 'non-discharge' Penning trap-type device.

(PS. I take the analogy that I am sometimes like a thick brick as a complement. Ask a guy in a hurricane with an ingeniously made paper house if he thinks a thick brick house has any particular benefits! My thick-brick status suggests a solid and stubborn contempt for conventionally accepted axioms – I like that you recognise this in me! But that's no licence to go too far with the ad hominem comments.)

Polywells have very large circulating currents. It is a feature of the design. And they are developed with a DC magnetic field.

MSimon wrote:Polywells have very large circulating currents. It is a feature of the design. And they are developed with a DC magnetic field.

A device can 'circulate' particles without 'drawing' current. Do you mean you expect it to be very heavy on pulling an electron current (from the electron guns)?

chrismb wrote:

MSimon wrote:Polywells have very large circulating currents. It is a feature of the design. And they are developed with a DC magnetic field.

A device can 'circulate' particles without 'drawing' current. Do you mean you expect it to be very heavy on pulling an electron current (from the electron guns)?

chris,

I'm sure you are aware that tuned circuits circulate current that is many times the current drawn and the ratio is defined by the Q. The equivalent in a Polywell is the GWB.

What was that about bricks again?

MSimon wrote: What was that about bricks again?

What about them? I'm sorry you feel like a brick now.

Yes, I started talking about current drawn, and you've started talking about current recirculating. What's your point, wrt Polywell's current-drawn?

chrismb wrote:

MSimon wrote: What was that about bricks again?

What about them? I'm sorry you feel like a brick now.

Yes, I started talking about current drawn, and you've started talking about current recirculating. What's your point, wrt Polywell's current-drawn?

It is possible to have lots of internal current with little current drawn if the set up is right.

MSimon is dancing around saying that starting cold it will take the electron guns a while to pump enough electrons into the wiffle ball while electrons in already continue to circulate. As I am understanding him.

How much does the Polywell suck up? This will be one measure I judge it by.

I asked Nebel this question a ways back. I think he said they were looking at about 5MW for a 100MW reactor.

There are two reasons for current -- to replace cold electrons with hot ones, and to replace losses to the Magrid.

Anyways, I thought the great thing about tokamaks is that they were supposed to ignite and not really require any additional energy at that point, but if they still need huge currents for confinement that seems like a big problem. How many MW will ITER pull past ignition?

Professor Science wrote:MSimon is dancing around saying that starting cold it will take the electron guns a while to pump enough electrons into the wiffle ball while electrons in already continue to circulate. As I am understanding him.

That is correct. With "long time" in this context being on the order of milliseconds.

TallDave wrote:

How much does the Polywell suck up? This will be one measure I judge it by.

I asked Nebel this question a ways back. I think he said they were looking at about 5MW for a 100MW reactor.

There are two reasons for current -- to replace cold electrons with hot ones, and to replace losses to the Magrid.

Anyways, I thought the great thing about tokamaks is that they were supposed to ignite and not really require any additional energy at that point, but if they still need huge currents for confinement that seems like a big problem. How many MW will ITER pull past ignition?

Don't forget the accelerator current from ions. It is not just the electron guns.

BTW if Rick said 5 MW (I think that is correct for pBj) it means they are planning on operating at the resonance peak of B11 (.1 barns). Going up to the actual peak (1.2 barns) would more than double that requirement.

MSimon wrote: It is possible to have lots of internal current with little current drawn if the set up is right.

I'm not really sure you've got the essence of the thread. My point is that I don't see how you can ever have a useful energy confinement time with a discharge method and Polywell's looking half-like a discharge method to me. So I was looking to see a) if that's right (to date) and b) what are the solutions to up its energy confinement time with improved ExB confinement.

At the very least, the only actual images I've seen of an 'active' Polywell show a ball of unit-eV-looking plasma which to my mind is indicative of discharge recombination emissions. We don't really want to be seeing anything like that, it's just an image depicting pure losses of the type a working fusion device just won't be able to tolerate. I presume it was just a chamber cleaning plasma, or something, because if it was running at fusible energies then I would expect to see just Balmer emissions, and very little of them as well.

Well, if the Polywell is running in discharge mode it's not working. There aren't supposed to be very many neutrals, and recombination should be almost impossible at the envisioned operating energies. It's supposed to be a particle accelerator, with very low leakage rates for trapped electrons, even lower rates for ions, and no other energy loss mechanisms of note (except maybe bremsstrahlung).

As you note, the energy confinement time is the relevant parameter, and according to Dr. Nebel it looks promising. Ionization via electron collisions is fine if the ion residence time (and therefore fusion fraction) is high enough. Although it is interesting that the recent solicitations have made much of ion guns for some reason...

WB-6 had an emitter current of 40 A peak. Then Paschen discharge took over and dumped the whole mess to the walls at over 4000 A, ending the run. If it's running in discharge mode it's not working.

WB-7 had an emitter current of 40 A peak. Then Paschen discharge took over and dumped the whole mess to the walls at over 4000 A, ending the run. If it's running in discharge mode it's not working.

How did we find out about WB-7? This is the first I've heard of any WB-7 data.

93143 wrote:Well, if the Polywell is running in discharge mode it's not working. There aren't supposed to be very many neutrals, and recombination should be almost impossible at the envisioned operating energies. It's supposed to be a particle accelerator, with very low leakage rates for trapped electrons, even lower rates for ions, and no other energy loss mechanisms of note (except maybe bremsstrahlung).

As you note, the energy confinement time is the relevant parameter, and according to Dr. Nebel it looks promising. Ionization via electron collisions is fine if the ion residence time (and therefore fusion fraction) is high enough. Although it is interesting that the recent solicitations have made much of ion guns for some reason...

WB-7 had an emitter current of 40 A peak. Then Paschen discharge took over and dumped the whole mess to the walls at over 4000 A, ending the run. If it's running in discharge mode it's not working.

Yes, this is another expression of my concerns. So, what I'm proposing here in this thread is that, presuming this 'threat' of it running in discharge mode is a real concern, rather than getting stressed waiting to see what it does so I'm asking if there are any ways to improve the ExB type trapping (because, irrespective of what it does or doesn't do, any improvement in this regard will be an improvement anyhow and can only be a 'good-thing').

Aero wrote: How did we find out about WB-7? This is the first I've heard of any WB-7 data.

Good catch. I meant WB-6...