Miniaturizing Focus Fusion

[The_Programer]

I have been reading about mobile and deploy-able Focus Fusion Reactors and have a couple of ideas to offer.

For some of the applications (aircraft) weight and size are a big issue, most of the weight and size are concentrated in to three areas: Shielding, Capacitors and Cooling.

Idea #1:
Most of the size and weight is in the neutron moderator (is that the right word? I mean the material that slows down the neutrons, usually water). I realized that the neutrons could be trapped inside a container filled with water and Boron10, by using a neutron reflector wrapped around the water container (http://en.wiki.org/wiki/Neutron_reflector) something like the attached pic1. The neutrons would bounce around until they where slowed down enough to be captured by Boron10. Would this work? Would the increased radiation levels cause problems? Would the extra neutrons interfere with the main reaction?

Idea #2:
Could superconductors be used instead of capacitors? Something like http://en.wiki.org/wiki/SMES only on a much smaller scale. Can superconductors stand the pulsed currents? I know they have problems with AC current, does this apply to rapid pulses as well? Would the rapidly changing magnetic field cause problems (health, stress, etc)? One advantage is that switching may not be a problem, I remember reading somewhere that current stored in a superconducting ring could be released by connecting two non-superconducting leads to the ring, then warming up the section of the ring between the the leads to something past its Tc point, thus making the warm section of the ring non-conductive and routing the stored energy through an external circuit (in this case the DPF device). Does this happen fast enough to be used in a DPF device?

Idea #3:
Do the outer electrodes need space between them and the vacuum chamber wall? Or could they be cut in half length wise, and one half be glued to the chamber wall? Something like pic2. The chamber wall would need to be non-conductive which might cause problems(finding a matériel that is non-conductive, strong enough to contain a vacuum, doesn’t release gases into the vacuum, and doesn’t get radioactive under neutron bombardment).

pic1 is to the left and pic2 to the right.

[Aeronaut]

Yes, neutron moderator is what the water shield does. Water was chosen for the high hydrogen content and low cost, so reducing shielding weight will decrease it’s effectiveness. The ability to do this in good conscience will vary with each installation. In the case of mobile installations, I would think no reduction would be conscionable. In large aircraft installations, several hundred tons of fuel and fuel system are no longer needed, which helps immensely.

Point #2 I’m not able to comment on.

Regarding Point 3, the DPF can be designed with a single piece cathode, which could double as the vacuum chamber wall.

[The_Programer]

Aeronaut wrote: The ability to do this in good conscience will vary with each installation. In the case of mobile installations, I would think no reduction would be conscionable. In large aircraft installations, several hundred tons of fuel and fuel system are no longer needed, which helps immensely.

I was thinking something like a laser, only in reverse. The neutrons bounce back and forth through the water slowing down until the can be absorbed by Boron10. I personal do not wish to be close to an unshielded reactor and would never reducing shielding, I proposing smaller and potentially as or more effective shielding.

Aeronaut wrote: Regarding Point 3, the DPF can be designed with a single piece cathode, which could double as the vacuum chamber wall.

Why did they chose a cluster of cathodes instead of a single piece one? Do the filaments still form properly on a single piece cathode? If the plasma sheath is evenly distributed wouldn’t it skip the filament merge stage? Would the sheath be evenly distributed? Would miniature defects cause the sheath to concentrate in unstable ways?
Please don’t think I’m demanding answers, I’d just like to fill in the gaps in my information/understanding.

[jamesr]

I thought the axial phase of the plasma was like a snowplow pushing all the gas in front of its bow-shock and ionising it – so increasing the density of the sheath as it sweeps down.

If the cathode was one piece then there is nowhere for gas to fill in behind the sheath, creating a low pressure area behind it. This back-pressure would slow down the sheath and reduce the energy of the focus.

As for the filamentation -it will always happen when you have a current flowing through a plasma. These filaments will also always go kink-unstable at some point (its in the nature of plasmas). But in order to get consistent firing of the DPF you want the instabilities to be seeded at the same point every pulse.

going back to #1 – neutron reflectors have to be made of heavy elements and are never perfect (think firing ping pong balls at an array of skittles). They just bounce around off the atoms in the reflector quickly loosing sense of their original direction, some then find their way back to a surface and come out again.
Lighter neutron moderators can be made of stuff like polythene or paraffin wax, as these have much higher hydrogen to overall density ratios than water. But only for neutron fluxes that are low enough that you don’t have to worry about the heat deposited in them.

[JimmyT]

The_Programer wrote: I have been reading about mobile and deploy-able Focus Fusion Reactors and have a couple of ideas to offer.

For some of the applications (aircraft) weight and size are a big issue, most of the weight and size are concentrated in to three areas: Shielding, Capacitors and Cooling.

Idea #1:
Most of the size and weight is in the neutron moderator (is that the right word? I mean the material that slows down the neutrons, usually water). I realized that the neutrons could be trapped inside a container filled with water and Boron10, by using a neutron reflector wrapped around the water container (http://en.wiki.org/wiki/Neutron_reflector) something like the attached pic1. The neutrons would bounce around until they where slowed down enough to be captured by Boron10. Would this work? Would the increased radiation levels cause problems? Would the extra neutrons interfere with the main reaction?

Back when Rutherford first fired particles at materials and witnessed scattering, we learned what a small part of any materials volume is occupied by it’s nucleus. Only a small fraction of the particles were deflected. Most simply went straight through the targets as though it were not even there. Yet this is precisely the way that neutron reflectors work. Some materials have bigger nuclei or have them more densely packed (Beryllium) making them more effective. But even then, only a small portion of the incident particles are reflected. These materials are only called neutron reflectors compared with the even poorer reflective ability of other materials. But don’t think of them as a mirror. Any more than you would think of highly polished chicken wire as a light mirror. It does reflect some back doesn’t it?

[jamesr]

JimmyT wrote:

I have been reading about mobile and deploy-able Focus Fusion Reactors and have a couple of ideas to offer.

For some of the applications (aircraft) weight and size are a big issue, most of the weight and size are concentrated in to three areas: Shielding, Capacitors and Cooling.

Idea #1:
Most of the size and weight is in the neutron moderator (is that the right word? I mean the material that slows down the neutrons, usually water). I realized that the neutrons could be trapped inside a container filled with water and Boron10, by using a neutron reflector wrapped around the water container (http://en.wiki.org/wiki/Neutron_reflector) something like the attached pic1. The neutrons would bounce around until they where slowed down enough to be captured by Boron10. Would this work? Would the increased radiation levels cause problems? Would the extra neutrons interfere with the main reaction?

Back when Rutherford first fired particles at materials and witnessed scattering, we learned what a small part of any materials volume is occupied by it’s nucleus. Only a small fraction of the particles were deflected. Most simply went straight through the targets as though it were not even there. Yet this is precisely the way that neutron reflectors work. Some materials have bigger nuclei or have them more densely packed (Beryllium) making them more effective. But even then, only a small portion of the incident particles are reflected. These materials are only called neutron reflectors compared with the even poorer reflective ability of other materials. But don’t think of them as a mirror. Any more than you would think of highly polished chicken wire as a light mirror. It does reflect some back doesn’t it?

I find your analogy is a little misleading. Neutrons are uncharged – so their chance of being scattered is even smaller than the charged alphas Rutherford’s assistants observed coming back off gold. But mainly – it is not a surface effect – since the chances of collision are so low the neutrons travel deep into the material before scattering. The reflection comes from many scatters deep in the material turning the neutron by different angles (most small). After a while some neutrons have the chance of being turned by a large enough angle to make there way back to the surface they entered from.

The mean free path (ie average distance between collisions) of a fast neutron in steel for example is around 6cm

So think many millions of layers of very fine chicken wire and you’re a little closer.

[JimmyT]

jamesr wrote:

I have been reading about mobile and deploy-able Focus Fusion Reactors and have a couple of ideas to offer.

For some of the applications (aircraft) weight and size are a big issue, most of the weight and size are concentrated in to three areas: Shielding, Capacitors and Cooling.

Idea #1:
Most of the size and weight is in the neutron moderator (is that the right word? I mean the material that slows down the neutrons, usually water). I realized that the neutrons could be trapped inside a container filled with water and Boron10, by using a neutron reflector wrapped around the water container (http://en.wiki.org/wiki/Neutron_reflector) something like the attached pic1. The neutrons would bounce around until they where slowed down enough to be captured by Boron10. Would this work? Would the increased radiation levels cause problems? Would the extra neutrons interfere with the main reaction?

Back when Rutherford first fired particles at materials and witnessed scattering, we learned what a small part of any materials volume is occupied by it’s nucleus. Only a small fraction of the particles were deflected. Most simply went straight through the targets as though it were not even there. Yet this is precisely the way that neutron reflectors work. Some materials have bigger nuclei or have them more densely packed (Beryllium) making them more effective. But even then, only a small portion of the incident particles are reflected. These materials are only called neutron reflectors compared with the even poorer reflective ability of other materials. But don’t think of them as a mirror. Any more than you would think of highly polished chicken wire as a light mirror. It does reflect some back doesn’t it?

I find your analogy is a little misleading. Neutrons are uncharged – so their chance of being scattered is even smaller than the charged alphas Rutherford’s assistants observed coming back off gold. But mainly – it is not a surface effect – since the chances of collision are so low the neutrons travel deep into the material before scattering. The reflection comes from many scatters deep in the material turning the neutron by different angles (most small). After a while some neutrons have the chance of being turned by a large enough angle to make there way back to the surface they entered from.

The mean free path (ie average distance between collisions) of a fast neutron in steel for example is around 6cm

So think many millions of layers of very fine chicken wire and you’re a little closer.

We are talking airplane design here. Right?

[jamesr]

JimmyT wrote:
We are talking airplane design here. Right?

Neutron shielding is always going to be bulky (from the moderator/absorber part) and heavy (from the gamma shield), especially for the high energy neutrons from D+D or D+T. That’s the beauty of p+B11, the few neutrons you do get from side reactions are much lower energy. So you only need a relatively thin layer of borated polyethylene to slow & absorb them. After this you still need some heavy metal shielding to capture the gamma-rays produced in the neutron absorption reactions. The gamma shield will also partly double as a neutron reflector, as described above.

I’m sure if the DPF was in the tail or out on the wings it would be viable to put them in an airplane. The radiation levels would be down to below what pilots are getting from cosmic rays anyway. (cargo planes at least – passengers may take a little more convincing)

[The_Programer]

I wasn’t thinking of airplanes in particular, there is a thread elsewhere for that, but more general applications like cars, ships, trains, dirigibles, etc. I was looking at the wikipedia page on the Toyota Prius (http://en.wikipedia.org/wiki/Prius) and noticed that the total power in KW is ~100, 100KW happens to be 2% of 5MW, and was wondering if Focus Fusion would scale down that far and what the radiation levels would be at that size. I’m thinking about Issac Asimov’s Foundation series and how they had nuclear reactors the size of a walnut and used nuclear power for everything (they had personal shields that where nuclear powered).

[Aeronaut]

jamesr wrote:

We are talking airplane design here. Right?

Neutron shielding is always going to be bulky (from the moderator/absorber part) and heavy (from the gamma shield), especially for the high energy neutrons from D+D or D+T. That’s the beauty of p+B11, the few neutrons you do get from side reactions are much lower energy. So you only need a relatively thin layer of borated polyethylene to slow & absorb them. After this you still need some heavy metal shielding to capture the gamma-rays produced in the neutron absorption reactions. The gamma shield will also partly double as a neutron reflector, as described above.

I’m sure if the DPF was in the tail or out on the wings it would be viable to put them in an airplane. The radiation levels would be down to below what pilots are getting from cosmic rays anyway. (cargo planes at least – passengers may take a little more convincing)

So we’re not stuck with a 1 meter water jacket? How thick of a borated polyethylene jacket would be required to match the water’s shielding properties? I know this won’t scale down to a car, but this could open a lot of bus and truck applications if the bulk is ~25% to 50% of the current water jacket.

[Brian H]

Aeronaut wrote:
…

So we’re not stuck with a 1 meter water jacket? How thick of a borated polyethylene jacket would be required to match the water’s shielding properties? I know this won’t scale down to a car, but this could open a lot of bus and truck applications if the bulk is ~25% to 50% of the current water jacket.

Trucks have more flexibility in weight distribution. But really high-energy-density batteries will probably be available long before special FoFus for vehicles! Consider how much in-place generation there is to handle, first.

[Timo]

The_Programer wrote: I wasn’t thinking of airplanes in particular, there is a thread elsewhere for that, but more general applications like cars, ships, trains, dirigibles, etc. I was looking at the wikipedia page on the Toyota Prius (http://en.wikipedia.org/wiki/Prius) and noticed that the total power in KW is ~100, 100KW happens to be 2% of 5MW, and was wondering if Focus Fusion would scale down that far and what the radiation levels would be at that size. I’m thinking about Issac Asimov’s Foundation series and how they had nuclear reactors the size of a walnut and used nuclear power for everything (they had personal shields that where nuclear powered).

This is in my mind too. How small can we get? What are the physical limitations of boron+hydrogen fusion generator.

Can we put them in

a) Ships and submarines? Ships with basically unlimited cheap source of electricity is obviously the best place for those reactors. But how small ship?
b) Trains? Would there be enough space in locomotive for reactor?
c) Cars? Passenger cars are probably out of the question for quite a long time, but what about heavy-duty trucks? How small? Something like Liebherr T 282 B could probably fit one in.
d) Airplanes? Even if we put FF reactor inside, then what? Jets are faster than propeller powered planes. Would that even be suitable there?
e) Blimps? Unlimited range blimp could be useful for cargo transfer and maybe also as passenger sky-cruiser like ships.
f) Space? Satellites, space ships, Moon and Mars ships? Fusion reactor would be very good source for something like vasimr rocket, but how do we get that reactor in space?

[Brian H]

Timo wrote:
…

This is in my mind too. How small can we get? What are the physical limitations of boron+hydrogen fusion generator.

Can we put them in

a) Ships and submarines? Ships with basically unlimited cheap source of electricity is obviously the best place for those reactors. But how small ship?
b) Trains? Would there be enough space in locomotive for reactor?
c) Cars? Passenger cars are probably out of the question for quite a long time, but what about heavy-duty trucks? How small? Something like Liebherr T 282 B could probably fit one in.
d) Airplanes? Even if we put FF reactor inside, then what? Jets are faster than propeller powered planes. Would that even be suitable there?
e) Blimps? Unlimited range blimp could be useful for cargo transfer and maybe also as passenger sky-cruiser like ships.
f) Space? Satellites, space ships, Moon and Mars ships? Fusion reactor would be very good source for something like vasimr rocket, but how do we get that reactor in space?

Timo, is that you? Same Timo who infests and informs over at TeslaMotors forums? Welcome, buddy!

For trucks, consider that the total weight of the FF generator, including shielding, is expected to be about 2 tons. I don’t think you get it under the hood; it would have to be a special configuration.

As to going orbital, there are some old Air Force studies of DPF as an SSTO power source, using MHD drive. I believe the conclusion was that there was power to spare. If so, theoretically FF is the basis of a sci-fi one-ship-does-all vehicle! If I can find the links, I’ll post them.

[Aeronaut]

Hope you can find the links, Brian. A 20MW SSTO vehicle would be sweet!

[Timo]

Brian H wrote:
Timo, is that you? Same Timo who infests and informs over at TeslaMotors forums? Welcome, buddy!

Yes it is me. I finally decided to join after lurking quite a while. Actually I got my “membership” due a donation, I didn’t know it would lead to that, but here I am.

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