Building a WB-2 Polywell

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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Lelephant
Posts: 3
Joined: Mon Aug 13, 2012 11:20 pm

Building a WB-2 Polywell

Postby Lelephant » Tue Aug 14, 2012 5:10 am

Hi, this is my first post on the forum, and I came here because I have dreams of building a WB-2 style polywell.

Basically, I want something as small as possible that I can run experiments on. I'm not worrying at all (at the moment) about break-even or harvesting energy. This is purely experimental.

I know the basics of how the polywell runs, but nothing specific (e.g. I have no idea how to build an electromagnetic coil or how to run voltage through it, I don't know how much voltage I should run through it or what the pressure of deuterium gas inside the vacuum vessel should be, and things like that.)

I do know the basics about polywells, and I think I'm going to have a steel (is stainless steel necessary), spherical vacuum chamber with a camera viewport (to which I will attach a TV monitor, in order to safely view the fusion reaction), a gas line in, a valve for the vacuum, and a high voltage electrode port for the electron beam.

I'm assuming that, instead of using something like an electric gun from an old TV monitor I could simply use the electrode port that's likely to come with a scientific vacuum chamber to discharge the electrons toward the MaGrid of the WB-2. Of course I will use a pressure sensor, neutron detector, radiation counter and power supply.

My questions are:

1. How do I know if I have too many or too little electrons injected into the chamber?
2. What precautions should I take with the power supply, and how should I attach it to the electrode?
3. How do I know how much deuterium is safe to inject into the chamber?
4. How do I protect myself against neutron radiation? Would simple stainless steel do the job?
5. How long can I run it for? How can I calculate how long it's safe to run for?
6. If something starts to go wrong (it gets too hot, way too much pressure, radiation spike, etc.) how can I safely turn the machine off and remove all power?
7. How do I prepare the electromagnet coils and how can I calculate how much electricity is necessary? How do I power the coils once they're inside the vacuum chamber?
8. Is there anything else I'm overlooking? Are there any helpful monitors/detectors that I really could use? I'm experimenting with the efficiency of dd fusion and will attempt to go on to aneutronic fusion.

Keep in mind, my design was taken from a sample fusor diagram with very slight alterations.

Any help would be very much appreciated.

Edit: I know some of these topics are covered elsewhere in certain threads in this forum, but I'm looking for a beginner friendly guide -- or at least a "start here." Many of the topics that address say, coiling, don't actually tell one how to create the coil, nor do they talk about voltages run, and they often rely on previous knowledge that I would very much like to gain and need for other parts of my first polywell design.

ladajo
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Location: North East Coast

Postby ladajo » Tue Aug 14, 2012 3:00 pm

Have you read the FAQs?
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Lelephant
Posts: 3
Joined: Mon Aug 13, 2012 11:20 pm

Postby Lelephant » Tue Aug 14, 2012 7:58 pm

ladajo wrote:Have you read the FAQs?


Yes, I understand the theory that I read in the FAQ as well as physicsforum and basically everywhere else on the internet. I want specific information, or at least a link to a page where I could find specific information. I need to start from the beginning so most sources are difficult to understand with 0 engineering experience.

mattman
Posts: 456
Joined: Tue May 27, 2008 11:14 pm

Postby mattman » Thu Aug 16, 2012 2:38 pm

This might help, give you a place to start...

http://thepolywellblog.blogspot.com/201 ... ywell.html

mattman
Posts: 456
Joined: Tue May 27, 2008 11:14 pm

Postby mattman » Thu Aug 16, 2012 3:08 pm

1. How do I know if I have too many or too little electrons injected into the chamber?

IDK. You may need some electron emitters to get a small electron cloud going first to attract D2. Electron emission could be done by heating up a wire next to a voltage drop. This is called thermionic emission. You could then probably just release the D2 gas straight in. More electrons would come right off the D2 itself, when the D2 becomes an ion and loses its electrons. If you get a spark, you have too much electrons and D2 in the chamber.


2. What precautions should I take with the power supply, and how should I attach it to the electrode?

There is a cage outside the rings, and you would bias it. Bussard used 12,500 volts - a dangerous amount considering a typical wall socket is 120 volts and that can shock you. I think they used car batteries....


3. How do I know how much deuterium is safe to inject into the chamber?

IDK. You can estimate it. You may be able to treat the D2 like an ideal gas, and use PV=NRT to figure out how many D2 molecules you release in the chamber based on the volume, temperature and pressure of the gas. Bussard vacuum was 1E-7 torr and he released the gas at 300 militorr.

4. How do I protect myself against neutron radiation? Would simple stainless steel do the job?

IDK this either. The rings were probably made from stainless steel. Read this: http://thepolywellblog.blogspot.com/201 ... ation.html about halfway down there is a comparison of graphite, 316 stainless steel, neodymium, molybdenum, Tungsten-Carbide, boron, Teflon, and aluminum for the ring material (also many hard-to-find and relevant physical properties for polywells).

Teflon seems to be the material of choice for the "first timers", Both Joe Khachan and Mark Suppes built small (about the size of a coffee cup) devices from Teflon discs with wire spun around them. Joe screwed L brackets into his discs to hold them together and probably attached the rings to an aluminum bar. His device pushed apart with ~0.2 Newtons of force - barely any repulsive force. You can read this: http://thepolywellblog.blogspot.com/201 ... sults.html for analysis. Teflon gets brown and can be a pain to degas because of gas pockets stuck in there that take forever to leave.


5. How long can I run it for? How can I calculate how long it's safe to run for?

IDK. Bussard ran for microseconds. like 20 microseconds.

6. If something starts to go wrong (it gets too hot, way too much pressure, radiation spike, etc.) how can I safely turn the machine off and remove all power?

Shutting down the power should shut it down. The voltages & magnetic fields are designed to funnel material into the center. If you shut it down the fields vanish and material flies everywhere.



7. How do I prepare the electromagnet coils and how can I calculate how much electricity is necessary? How do I power the coils once they're inside the vacuum chamber?

IDK. The rings are designed so that the corner and the axis fields are roughly the same. You can estimate the field strength using the Biot-Savart law. In the post, this was estimated to be ~193 and ~197 gauss for WB-6, Bussard put 4000 amps through each one of his rings. Disclaimer: Bussard estimated the magnetic field strength as 80 - 100 gauss at the corner and axis - though I cannot see how he got that answer. Remember that copper wire runs through all 6 rings, continuously. That means that 4000 amps would run through each ring, individually. If you make the rings smaller (say 4" a side) you should need a smaller current.


8. Is there anything else I'm overlooking? Are there any helpful monitors/detectors that I really could use? I'm experimenting with the efficiency of dd fusion and will attempt to go on to aneutronic fusion.

Yes - sparking. Watch out for sparking. Mainly from the outside cage to the rings. You will need neutron detectors and the rumor is they need to be shielded (allot) or you will get false counts. Especially when you are just starting out, the machine you build won’t give off much neutron signal compared to the neutron background noise.
Last edited by mattman on Fri Aug 31, 2012 2:32 pm, edited 1 time in total.

D Tibbets
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Joined: Thu Jun 26, 2008 6:52 am

Postby D Tibbets » Thu Aug 16, 2012 9:44 pm

1. How do I know if I have too many or too little electrons injected into the chamber?

No an issue. You need to provide enough electrons to reach Beta-1. If you provide too many electrons they just spill out and are irrelevent (within limits).


2. What precautions should I take with the power supply, and how should I attach it to the electrode?

All of the high voltage knowledge and precautions . The high voltage cannot only injure you, if the electricity can penetrate your skin, it can kill you. And it is the current that kills. Anything over 50 ma is considered potentially lethal. There are other factors but this is a basic rule of thumb. The voltage determines how well the the electricity penetrates and the current kills- usually by stopping the heart.


3. How do I know how much deuterium is safe to inject into the chamber?

Who cares . it is a non issue in a small machine with less than phenomenal B fields. The fusion reactions are far to few to be a radiation or heat issue. X-ray production is a more significant issue, and is related to plasma energy and mostly wall collisions in these small machines.


4. How do I protect myself against neutron radiation? Would simple stainless steel do the job?

Again it is a non issue, unless you are pushing well past the performance of WB6. The non nuclear X-ray production may be a concern if you are pushing much past ~10-15 thousand volts. Then the x-rays start to penetrate a thin stainless steel shell , along with the glass viewports.


5. How long can I run it for? How can I calculate how long it's safe to run for?

Yes, you can run it for as long as your magnets stay cool despite the resistance in the coils. The heating from the plasma and x-rays will probably be a trivial concern. If it is producing one micro Rem of neutron radiation per hour of operation and you sit by an operating machine for weeks, the dose would build up, possibly even to levels equivalent to taking an airplane flight. Rember the key componets are neutron flux per unit of time,the exposure time, shielding, and distance.


6. If something starts to go wrong (it gets too hot, way too much pressure, radiation spike, etc.) how can I safely turn the machine off and remove all power?

It will not get hot from fusion. Even WB6 only produced ~ 1 milliwatt of fusion energy. This is not an ignition machine, it is an amplifier. There is no runaway, or criticality concerns. The Tokamak is an ignition machine, and could arguably "run away, but the fuel present limits this to relatively small excursions that would be easily controlled or even stopped merely by managing the fuel flow into the machine. It is not like fission fuel rods where a tremendous amount of energy is vulnerably stored.

If you are imputing ~ 10,000 Watts of power, most of it will end up as heat. Consideration of machine size and thermal mass will help to determine how much it warms up. Amateur fusors may heat up like weak toaster ovens (perhaps ~500 to 1000 watts of heating). Keep in mind that heating may not be even . Hot plasma may heat a wire grid to incandescence, or melting.
Things can melt but other than electrode damage it is no big deal.
The exception is the electromagnets. They are in vacuum so do not dissipate heat well. If there is not active cooling (or it fails) the wires in the electromagnet can heat enough to melt electrical insulation, and short out, either to adjacent wires, of to the case (this is what happened to WB6). This could damage the magnet and chemically contaminate the chamber. So long as you have reasonable fusing it would not go beyond this point.

7. How do I prepare the electromagnet coils and how can I calculate how much electricity is necessary? How do I power the coils once they're inside the vacuum chamber?

There are straight forward formulas.
Essentially the amp turns determines the magnetic field strength. geometry and medium also plays a role and can be complicated. Start looking up electromagnets.
The current * number of turns. The voltage needed is dependent on the resistance of the length of copper wire and can be determined from Ohm's law. The resistance of the copper wire can be looked up, the length is known, and the amps is known (derived from targeted magnet strength). Plan on short magnet run times (less than a few seconds) to minimize resistive heat build up, etc.
Providing power is simple. A wire connection. That said, the magnets will need a case that seals the magnet wire inside. The connecting wire entrance also needs to be sealed. I can speak from experience that hot melt glue is bad. A slow set epoxy may work, at least for prototyping. The magnet needs to be sealed due to outgassing concerns. You cannot have just a role of wire held together with wire ( note though that some have done just that) Short run times and low concern about outgassing contamination, allows this.


8. Is there anything else I'm overlooking? Are there any helpful monitors/detectors that I really could use? I'm experimenting with the efficiency of d

Yes, you overlooking a lot of stuff. Studying vacuum technology, fore pumps, diffusion, turbo molecular pumps, etc. Pashin discharge and how it changes with vacuum level, high voltage issues and equipment, outgassing considerations, chemical contamination issues (the chamber, not you),other vacuum issues.

As far as neutron detection issues, if you are concerned about noise with electronic counters, there are bubble detectors which are fairly sensitive and practically immune from any noise issues.

Some musings on neutron detection from D-D fusion in a WB2 type device. Using WB6 as the baseline of 500,000,000 neutrons per second flux.
Assume the WB2 like project has 100 gauss,and a radius of 5 cm. Scaling from WB6 would result in a neutron flux of ~ 2,000 neutrons per second at best. This level is detectable if you run long enough. Probably at least a few seconds run time would be needed. In amateur fusors generally several tens of thousands of neutrons/ sec. fluxes are needed for detection. Which means you would need to boost the size, or preferably the magnetic field strength to have a good likelyhood of detecting fusion through neutron counts. The problem with scaling the magnetic field is mostly the resistive heating of the magnet wire windings.


PS: Starting with a WB1 permanent magnet type arrangement may be a convenient intermediate. This would allow you to tackle the vacuum, high voltage and other operation issues, while you are perfecting the electromagnet construction.

Dan Tibbets
Last edited by D Tibbets on Sat Aug 18, 2012 8:55 pm, edited 1 time in total.
To error is human... and I'm very human.

happyjack27
Posts: 1435
Joined: Wed Jul 14, 2010 5:27 pm

Re: Building a WB-2 Polywell

Postby happyjack27 » Sat Aug 18, 2012 1:14 am

I'm a layman so take my answers with a grain of salt.

Lelephant wrote:Hi, this is my first post on the forum, and I came here because I have dreams of building a WB-2 style polywell.

Basically, I want something as small as possible that I can run experiments on. I'm not worrying at all (at the moment) about break-even or harvesting energy. This is purely experimental.

I know the basics of how the polywell runs, but nothing specific (e.g. I have no idea how to build an electromagnetic coil or how to run voltage through it, I don't know how much voltage I should run through it or what the pressure of deuterium gas inside the vacuum vessel should be, and things like that.)

I do know the basics about polywells, and I think I'm going to have a steel (is stainless steel necessary), spherical vacuum chamber with a camera viewport (to which I will attach a TV monitor, in order to safely view the fusion reaction), a gas line in, a valve for the vacuum, and a high voltage electrode port for the electron beam.

I'm assuming that, instead of using something like an electric gun from an old TV monitor I could simply use the electrode port that's likely to come with a scientific vacuum chamber to discharge the electrons toward the MaGrid of the WB-2. Of course I will use a pressure sensor, neutron detector, radiation counter and power supply.

My questions are:

1. How do I know if I have too many or too little electrons injected into the chamber?

When it asplodes . Kidding the coils should have a ositive charge. If the system is net negative you'll lose electrons to the chamber walls. If net positive your ion confinement will be worse. So make it net neutral. You will have to calculate.
2. What precautions should I take with the power supply, and how should I attach it to the electrode?

Make sure it's off and any capacitors are fully drained. Rubber gloves are unfashoinable, but so is baldness.
3. How do I know how much deuterium is safe to inject into the chamber?

Its not a safety hazard, but you do have to balance the pressure with the electromagnetic force. That is key to the whole thing. That's "b=1". Meaning you have to measure the gas loss through the vacuum pump very precisely and inject enough to keep the net pressure in the chamber at a constant proportion to the field strength.
4. How do I protect myself against neutron radiation? Would simple stainless steel do the job?

lead is probably better And cheaper. But distance does great. Above all get anuwtron detector.
5. How long can I run it for? How can I calculate how long it's safe to run for?

Main concerns are capacitor charge and not blowing the coils.

Just make sure your. Coils are very safe from shorts and overheating, and in all likelihood you'll be limited by capacitor charge.



6. If something starts to go wrong (it gets too hot, way too much pressure, radiation spike, etc.) how can I safely turn the machine off and remove all power?

Just turn off the coils. Turning off vacuum first can cause arcing. It will stay in the chamber but could damage it. That's it. Cut the coil power and it's as inert as a rock in a nanosecond.
7. How do I prepare the electromagnet coils and how can I calculate how much electricity is necessary? How do I power the coils once they're inside the vacuum chamber?
8. Is there anything else I'm overlooking? Are there any helpful monitors/detectors that I really could use? I'm experimenting with the efficiency of dd fusion and will attempt to go on to aneutronic fusion.

Keep in mind, my design was taken from a sample fusor diagram with very slight alterations.

Any help would be very much appreciated.

Edit: I know some of these topics are covered elsewhere in certain threads in this forum, but I'm looking for a beginner friendly guide -- or at least a "start here." Many of the topics that address say, coiling, don't actually tell one how to create the coil, nor do they talk about voltages run, and they often rely on previous knowledge that I would very much like to gain and need for other parts of my first polywell design.

happyjack27
Posts: 1435
Joined: Wed Jul 14, 2010 5:27 pm

Postby happyjack27 » Sat Aug 18, 2012 1:52 am

How much power? Magnetic field strength I.e current to the coils: as far as my simulations can tell: as high as you can get it without frying anything. That leaves only coil voltage: cool voltage is tied to both electron gun voltage and gas pressure in the chamber. The system must be net neutral, and there needs to be a voltage diff between the electron guns and the coils in order for a virtual electrode to form and sustain at better than break-even power levels - or so goes the theory, at least. Idk what the optimal amount is. But the amount affects the ratio of confinement to energy loss, presumably.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Postby D Tibbets » Sat Aug 18, 2012 9:16 pm

happyjack27 wrote:How much power? Magnetic field strength I.e current to the coils: as far as my simulations can tell: as high as you can get it without frying anything. That leaves only coil voltage: cool voltage is tied to both electron gun voltage and gas pressure in the chamber. The system must be net neutral, and there needs to be a voltage diff between the electron guns and the coils in order for a virtual electrode to form and sustain at better than break-even power levels - or so goes the theory, at least. Idk what the optimal amount is. But the amount affects the ratio of confinement to energy loss, presumably.


Actually, net neutral is the last thing you want. It is nit picking, but one of the essential properties is that there is not net neutrality. There must be an excess of electrons. Granted this bias is only ~ 1 part per million, but still essential. With gas puffing ion source this bias is naturally maintained, mostly due to less than 100% ionization efficiencecy. Ionization is almost totally due to electron collisions, and the ionizatios adds corresponding stripped off electrons to the mix, thus does not change the ion/ electron ratio. You need to flood the magrid with enough neutral gas molecules that the ionization process is saturated- in order to get the maximum internal density/ Wiffleball. Not too much though, as this shortens the time to the beginning of arcing. This might benefit from precision but it is not absolutely essential, there is a considerable amount of wiggle room as demonstrated by the simple apparatus used in WB6.

With ion guns, the system may need active and precise control of the ion flux.

Dan Tibbets
To error is human... and I'm very human.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Postby D Tibbets » Sat Aug 18, 2012 9:51 pm

I edited my second prevous post to make it more readable, but this issue may deserve it's pwn isolated emphasis.

Fusion power serges are not a primary problem. Contrasted to Fission power, where a fuel rod contains a lot of fuel and hot decaying secondary products that is held at the edge of criticality , fusion fueled reactors are different for the most part. There is not feedback criticality. In ignition machines like Tokamaks, the plasma is heated to conditions where the fusion maintains the temperature and thus promotes more fusion of any fuel present. In theory this might lead to a run away reaction, but is pratically limited by the amount of fuel present. Only relatively tiny amount of fuel is introduced per second, or perhaps controlled to sub millisecond time scales. There is no huge reservoir of fuel that can be consumed by a run away, even if it did occur. It would be a small burp. I suspect it would be less of a structural concern than the several macro instability processes that challenges tokamaks, It could be shut down by turning off the magnets, but this is far more problematic than any fusion caused small excursions in the system


In a Polywell, it is not an ignition machine. There is no plasma heating feedback involved at all. So any Tokamak miner concern is absent. If there could be some resonant pressure wave or central focus excursion, it would involve processes on the micro second or even nano second time scales and the fuel inside the machine on these scales is small, so the fuel is consumed and the reaction stops. There is a possibility that the Pollywell may actually be designed to operate in this pulsating fashion. The point is that whether a smooth steady state or pulsating machine, the excursions are well within the engineering limits of the machines. If you did wish to dampen the reaction in a polywell there are multiple knobs that can be adjusted on micro second time scales. Decrease ion input, decrease electron input, decrease accelerating voltage, possibly adjust magnetic field (if not pure superconductor magnets). In a large commercial Polywell it might be reasonable to watch and control these unlikely small excursions. In a small research reactor, even as big a WB8 machine, the possible excursions are trivial and can be ignored from a safty or machine durability standpoint. Again from a research standpoint, any of these pulsation type excursions from a steady state might be useful and persueing them would help to better characterize the machine.

In short, subtle excursions and plasma characteristics may be important to optimize the machine, but has zero safety consequences in these research machines. The magnitude is just way too small.

Dan Tibbets
To error is human... and I'm very human.

Lelephant
Posts: 3
Joined: Mon Aug 13, 2012 11:20 pm

Postby Lelephant » Sun Aug 19, 2012 6:08 am

First of all, general questions (some are meant to be for D Tibbets but I can't remember which):

1. Wouldn't physically running a wire into the vacuum chamber to power the coils compromise the vacuum of a belljar vacuum chamber?
2. How to keep my magnets cool and how to measure their heat?
3. How can I calculate emission rates of x-rays, neutrons, etc?
4. How do I detect aneutronic fusion?
5. Is aneutronic possible with permanent magnets and WB-1 or WB-2 configuration?
5. Is D2 fusion possible with permanent magnets and WB-1 configuration?
6. Do I bias the cage of permanent magnets? Why? To what degree?
7. How do I measure the potential well and electron to ion ratio?
8. What proportions should I maintain?
9. Permanent magnets vs. coils?

Mattman:
mattman wrote: IDK. You may need some electron emitters to get a small electron cloud going first to attract D2. Electron emission could be done by heating up a wire next to a voltage drop. This is called thermionic emission. You could then probably just release the D2 gas straight in. More electrons would come right off the D2 itself, when the D2 becomes an ion and loses its electrons. If you get a spark, you have too much electrons and D2 in the chamber. 


1. What sort of voltage drop would I use and how would I regulate it to emit the correct quantity of electrons?
2. Would I shut it off just by turning off the power going toward the voltage drop?
3. How is the D2 ionizing in your explanation?
4. Why would a spark mean I have too many electrons as well as too much D2?

mattman wrote:Teflon seems to be the material of choice for the "first timers", Both Joe Khachan and Mark Suppes built small (about the size of a coffee cup) devices from Teflon discs with wire spun around them. Joe screwed L brackets into his discs to hold them together and probably attached the rings to an aluminum bar. His device pushed apart with ~0.2 Newtons of force - barely any repulsive force. You can read this: http://thepolywellblog.blogspot.com/2011/07/modeling-some-real-results.html for analysis. Teflon gets brown and can be a pain to degas because of gas pockets stuck in there that take forever to leave. 


5. Why would he attach them to an aluminum bar?
6. Why is repulsive force important and how can I measure the repulsive force of my rings?

mattman wrote: Yes - sparking. Watch out for sparking. Mainly from the outside cage to the rings. You will need neutron detectors and the rumor is they need to be shielded (allot) or you will get false counts. Especially when you are just starting out, the machine you build won’t give off much neutron signal compared to the neutron background noise.


7. How can I calculate if sparking will occur and prevent it?
8. Why is sparking bad?
9. Could sparking be beneficial to fusion?

D Tibbets:
D Tibbets wrote: Providing power is simple. A wire connection. That said, the magnets will need a case that seals the magnet wire inside. The connecting wire entrance also needs to be sealed. I can speak from experience that hot melt glue is bad. A slow set epoxy may work, at least for prototyping. The magnet needs to be sealed due to outgassing concerns. You cannot have just a role of wire held together with wire ( note though that some have done just that) Short run times and low concern about outgassing contamination, allows this. 


1. How do I know I'm preventing outgassing and how can I measure outgassing?
2. How can I make sure the wire entrance is sealed and that the case is sealed?
3. Are there any pre-made, purchasable cases (where can I find cases)?
4. Why can't I have the coils exposed at such low operating levels if outgassing is a minor concern?

D Tibbets wrote:
Actually, net neutral is the last thing you want. It is nit picking, but one of the essential properties is that there is not net neutrality. There must be an excess of electrons. Granted this bias is only ~ 1 part per million, but still essential. With gas puffing ion source this bias is naturally maintained, mostly due to less than 100% ionization efficiencecy. Ionization is almost totally due to electron collisions, and the ionizatios adds corresponding stripped off electrons to the mix, thus does not change the ion/ electron ratio. You need to flood the magrid with enough neutral gas molecules that the ionization process is saturated- in order to get the maximum internal density/ Wiffleball. Not too much though, as this shortens the time to the beginning of arcing. This might benefit from precision but it is not absolutely essential, there is a considerable amount of wiggle room as demonstrated by the simple apparatus used in WB6. 

With ion guns, the system may need active and precise control of the ion flux. 


5. Could I detect fusion in a small model like the WB-2 by simply releasing D2 into the chamber?
6. How will it ionize by itself?
7. How can I make sure/calculate whether or not (or how much of it) will ionize?
8. Why are ion guns preferred if D2 will ionize anyway?
9. How can I actively and precisely control ion flux and compare it to other measurements in the system?
10. What proportions should I maintain?

Happyjack27:
happyjack27 wrote: Make sure it's off and any capacitors are fully drained. Rubber gloves are unfashoinable, but so is baldness. 


1. Do I need capacitors? Why?

happyjack27 wrote: Its not a safety hazard, but you do have to balance the pressure with the electromagnetic force. That is key to the whole thing. That's "b=1". Meaning you have to measure the gas loss through the vacuum pump very precisely and inject enough to keep the net pressure in the chamber at a constant proportion to the field strength. 


2. How do I do/measure all this?
3. What proportion should I maintain?

happyjack27
Posts: 1435
Joined: Wed Jul 14, 2010 5:27 pm

Postby happyjack27 » Sun Aug 19, 2012 10:24 pm

D Tibbets wrote:
happyjack27 wrote:How much power? Magnetic field strength I.e current to the coils: as far as my simulations can tell: as high as you can get it without frying anything. That leaves only coil voltage: cool voltage is tied to both electron gun voltage and gas pressure in the chamber. The system must be net neutral, and there needs to be a voltage diff between the electron guns and the coils in order for a virtual electrode to form and sustain at better than break-even power levels - or so goes the theory, at least. Idk what the optimal amount is. But the amount affects the ratio of confinement to energy loss, presumably.


Actually, net neutral is the last thing you want. It is nit picking, but one of the essential properties is that there is not net neutrality. There must be an excess of electrons. Granted this bias is only ~ 1 part per million, but still essential. With gas puffing ion source this bias is naturally maintained, mostly due to less than 100% ionization efficiencecy. Ionization is almost totally due to electron collisions, and the ionizatios adds corresponding stripped off electrons to the mix, thus does not change the ion/ electron ratio. You need to flood the magrid with enough neutral gas molecules that the ionization process is saturated- in order to get the maximum internal density/ Wiffleball. Not too much though, as this shortens the time to the beginning of arcing. This might benefit from precision but it is not absolutely essential, there is a considerable amount of wiggle room as demonstrated by the simple apparatus used in WB6.

With ion guns, the system may need active and precise control of the ion flux.

Dan Tibbets


I understand the plasma needs to be net negative, but I was including the coil charge. Surely if the system was net neg with respect to ground, and the chamber was grounded, there'd be a current from the electron guns to the chamber, and that would be an energy loss.

happyjack27
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Joined: Wed Jul 14, 2010 5:27 pm

Postby happyjack27 » Sun Aug 19, 2012 11:03 pm

If the charge of the whole system doesn't match that of the chamber, that will create a voltage gradient that will induce a current. To maintain that voltage gradient, you have to constantly pump in energy equal to the current. If you don't do this, then the system becomes net neutral relative to the chamber, like I said.

I don't see the benefit of having a voltage gradient on the chamber, unless you're using it as an electron source (not a bad idea) but that would mean a net positive system.

KitemanSA
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Location: OlyPen WA

Re: Building a WB-2 Polywell

Postby KitemanSA » Mon Aug 20, 2012 2:08 am

Lelephant wrote:Hi, this is my first post on the forum, and I came here because I have dreams of building a WB-2 style polywell.

Basically, I want something as small as possible that I can run experiments on. I'm not worrying at all (at the moment) about break-even or harvesting energy. This is purely experimental.
I hope that what you mean is that you plan to construct a machine about the SIZE of a WB2 but the configuration of a WB6 (or 7). WB2 had a square minor x-section, which didn't work very well.

If you want to do research, you may want to build something like the configuration of Bussard's proposed WB7, i.e., a square MAJOR planform.

happyjack27
Posts: 1435
Joined: Wed Jul 14, 2010 5:27 pm

Postby happyjack27 » Mon Aug 20, 2012 8:14 pm

Lelephant wrote:Happyjack27:
happyjack27 wrote: Make sure it's off and any capacitors are fully drained. Rubber gloves are unfashoinable, but so is baldness. 


1. Do I need capacitors? Why?



it's hard to imagine an electrical circuit that doesn't use capacitors somewhere.

in this case, to store and filter (remove fluctuations from) the massive amount of power you need. esp. if you plan on running it in pulsed mode.

happyjack27 wrote: Its not a safety hazard, but you do have to balance the pressure with the electromagnetic force. That is key to the whole thing. That's "b=1". Meaning you have to measure the gas loss through the vacuum pump very precisely and inject enough to keep the net pressure in the chamber at a constant proportion to the field strength. 


2. How do I do/measure all this?
3. What proportion should I maintain?


i wouldn't know how to measure it.

you're aiming to reach an exact balance over a spherical surface are somewhere between the exact center and the coils.


atmospheric pressure should really be near vaccum. among other reasons, to remove impurities, to prevent arcing, and to encourage a plasma state (i think). in truth, it's "electrostatic pressure" vs. "magnetic pressure" - electrostatic repulsion of the excess electrons, (esp. given that this is a plasma; that you're not dealing with neutral atoms, but charged ions and charged electrons, unattached to each other.), somewhat aided by the positive charge on the magrid. "the electromagnetic pressure" is really the magnetic "pressure" created by the current running through the coils.

if you create a surface where those two forces balance exactly, you are essentially creating a closed surface of zero electron flux. And whose first derivative is also zero. A 2-d "saddle point", if you will.

anyways, what you're balancing, is the net plasma charge (read:excess electrons), the coil charge, and the magnetic field from the coils. to a large extent this can be done theoretically with calculations (it helps to non-dimensionalize first), but no system is perfect, and i'm sure it will help to have some real-time empirical measurements and the ability to make on-the-fly minor corrections.

from what i recall reading about how they did this with the wb-6, is they just held one thing constant, while slowly varying the other one until they hit a spike in confinement efficiency (sudden drop in electron loss).

so it seems to me that some useful things to measure are the strength of electric and magnetic fields, and the amount of current and voltage lost to the grid and the chamber.


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