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http://powerandcontrol.blogspot.com/200 ... pdate.html
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Details On The WB-7 Experiments
I second that, if it's legally permissible for them to do so. This is very exciting stuff, and they could possibly benefit from our insights if they run into problems.It would be good if the polywell crew could converse on this list (or others if this is not to their liking). It would be a way to recruit a good deal of volunteer effort and free publicity.
I think a nuclear engineer might have such information. When the collision occurs between the proton and the boron nucleus, there's probably only a few angles of attack that will create the fused species ... and it might well be that the helium nuclei that emerge from the fused species exit at defined angles (or a range of angles) from the original trajectories. By collimating the protons and boron nuclei entering the plasma and defining their trajectories, it might be possible to predict where the alphas will emerge.GPecchia wrote:I have been wondering if there was a way to somehow direct the alpha particles to exit through the centers of the magnets.
Unfortunately I do not know the answer. And from reading the notes on WB-6, I do not know if Dr. Bussard knew either. The detectors for the neutrons were placed around the fusor and recorded neutron events during runs (I think three neutron strikes were recorded !). From these strikes they inferred many neutron emissions (i.e fusion) presumably because neutrons exit at all angles from a fusion event.
Regards,
Tony Barry
As a nuke-E I can tell you it would be tough. You've got 2 MeV particles and a .05 MV grid.
It would be easier to build the coils with a thick enough skin that they can handle the helium impacts and out gas it later. Alphas (helium nuclei) are easy to stop, so that's not really a problem for a long life time on the reactor.
Great article. I envy those guys working on WB-7 ! Good luck to them.
It would be easier to build the coils with a thick enough skin that they can handle the helium impacts and out gas it later. Alphas (helium nuclei) are easy to stop, so that's not really a problem for a long life time on the reactor.
Great article. I envy those guys working on WB-7 ! Good luck to them.
Thanks tonybarry and drmike for responding to my comments. I was worried about the coils becoming too hot.
tonybarry wrote: "As a nuke-E I can tell you it would be tough. You've got 2 MeV particles and a .05 MV grid."
If I understaind you correctly; it would be like trying to deflect a bullet with a badminton racquet.
I will read all of the Design and Theory forums and make further posts there. I will also figure out how to quote properly.
tonybarry wrote: "As a nuke-E I can tell you it would be tough. You've got 2 MeV particles and a .05 MV grid."
If I understaind you correctly; it would be like trying to deflect a bullet with a badminton racquet.
I will read all of the Design and Theory forums and make further posts there. I will also figure out how to quote properly.
Hello GPecchia,
drmike is the Nuke E. I am an elect. tech. who now works in biomed. doing fine assembly (catheter manufacture for research cardiologists). I remain interested in the polywell because (unlike ITER) I think it stands a chance of actually working ... if the engineering hurdles can be overcome.
The 2MeV alphas have significant kinetic energy which can be absorbed by either electric braking (i.e. climbing up the 2MV external grid voltage gradient) or by smashing into something solid. Since the polywell coils represent solid targets, and cannot be charged to 2MV as far as I understand, they must either run into the coils (the MaGrid) or escape through the holes. A positive charge on the coil surface would help keep off the alphas ... but the coils are living right next to the maximum electron density. If we charge them positively, the electrons are going to want to run closer to the coil and this would increase electron losses (which is the big killer of the polywell). It might be possible to line the facing side of the coil with something dense and nonmagnetic to act as "wear plates" so the coil does not suffer alpha strikes.
Neutrons remain the hardest bullets to deal with. They have significant kinetic energy and no electric charge to use as a handle to deflect or control them with. They just smash into whatever is in the way.
To some extent, the heat created from collisions can be removed via coolant (the MaGrid needs LH cooling anyway to stay superconducting) but if this is the major output of the polywell then the cooling will be a serious engineering hurdle. A good coolant for energy transfer gets as hot as possible with respect to the energy sink it flows through; but LH is about as bad a coolant for energy transfer as you can get. There's nothing even close to it to use as an energy sink ... LH is around 4 Kelvin.
Bussard's idea of using pB11 and doing all the major energy collection in the 2MV grid to collect alphas is a great scheme, as the major energy product of fusion becomes an electrically charged species whose kinetic energy is easily and directly transferable into electricity rather than thermal energy. Makes it a much more efficient system.
Regards,
Tony Barry
drmike is the Nuke E. I am an elect. tech. who now works in biomed. doing fine assembly (catheter manufacture for research cardiologists). I remain interested in the polywell because (unlike ITER) I think it stands a chance of actually working ... if the engineering hurdles can be overcome.
The 2MeV alphas have significant kinetic energy which can be absorbed by either electric braking (i.e. climbing up the 2MV external grid voltage gradient) or by smashing into something solid. Since the polywell coils represent solid targets, and cannot be charged to 2MV as far as I understand, they must either run into the coils (the MaGrid) or escape through the holes. A positive charge on the coil surface would help keep off the alphas ... but the coils are living right next to the maximum electron density. If we charge them positively, the electrons are going to want to run closer to the coil and this would increase electron losses (which is the big killer of the polywell). It might be possible to line the facing side of the coil with something dense and nonmagnetic to act as "wear plates" so the coil does not suffer alpha strikes.
Neutrons remain the hardest bullets to deal with. They have significant kinetic energy and no electric charge to use as a handle to deflect or control them with. They just smash into whatever is in the way.
To some extent, the heat created from collisions can be removed via coolant (the MaGrid needs LH cooling anyway to stay superconducting) but if this is the major output of the polywell then the cooling will be a serious engineering hurdle. A good coolant for energy transfer gets as hot as possible with respect to the energy sink it flows through; but LH is about as bad a coolant for energy transfer as you can get. There's nothing even close to it to use as an energy sink ... LH is around 4 Kelvin.
Bussard's idea of using pB11 and doing all the major energy collection in the 2MV grid to collect alphas is a great scheme, as the major energy product of fusion becomes an electrically charged species whose kinetic energy is easily and directly transferable into electricity rather than thermal energy. Makes it a much more efficient system.
Regards,
Tony Barry
The accelerator grid is charged positive at 50 Kv (or 200 KV depending). Its magnetic field is designed to deflect electrons. To deflect 2 MEV protons it would need a really huge magnetic field. On the order of 20T to 80T or more. Not practical.
So some alphas will hit the grid.
The first thing required is to make the grid as small as possible. So the first defense is geometry.
The second defense is cooling. The superconductors will be cooled directly with LHe at around 4K to 20K (depending on the superconductor used - I like MgB). Next to that will be vacuum. Next will be LN at 77K or so. Next will be another vacuum space. Finally there will be H2O.
If we can get the alpha impingement on the coil/grid lower than 300 KW/m sq no problem. That is about the limit for "ordinary" cooling. If it gets up to 1 MW/m sq life gets difficult because of the high pressures and high pumped volumes required.
So some alphas will hit the grid.
The first thing required is to make the grid as small as possible. So the first defense is geometry.
The second defense is cooling. The superconductors will be cooled directly with LHe at around 4K to 20K (depending on the superconductor used - I like MgB). Next to that will be vacuum. Next will be LN at 77K or so. Next will be another vacuum space. Finally there will be H2O.
If we can get the alpha impingement on the coil/grid lower than 300 KW/m sq no problem. That is about the limit for "ordinary" cooling. If it gets up to 1 MW/m sq life gets difficult because of the high pressures and high pumped volumes required.
An alternative material would be one that can take the impact without being destroyed, and can use the heat to anneal itself back to an original form. If it is large scale enough, the helium particles will out gas. Using water cooling to suck the remaining heat out is a great way to help maintain structure and generate energy.
It's just engineering details. Let's check the physics first. Once we prove the concept works, turning it into a power plant is just time and money!
It's just engineering details. Let's check the physics first. Once we prove the concept works, turning it into a power plant is just time and money!
Dr. Mike,
I'm 99% sure the physics will work out because every doubt I had on that score has been corroborated by independent sources. I believe Dr. B played it totally straight.
Dr. B thought the intercept area on a 100 MW reactor would be 20%. That is 20 MW. To say that it is "just engineering" underestimates the difficulties. You have to draw off that 20 MW within 3" or less of 4 Deg K.
It will not be "just engineering" it will be an engineering wonder. I have run the numbers. It will be very tough. I'm not worried about alpha impingement. As you point out that will be a small problem. It is the heat load that will be a killer.
I'm 99% sure the physics will work out because every doubt I had on that score has been corroborated by independent sources. I believe Dr. B played it totally straight.
Dr. B thought the intercept area on a 100 MW reactor would be 20%. That is 20 MW. To say that it is "just engineering" underestimates the difficulties. You have to draw off that 20 MW within 3" or less of 4 Deg K.
It will not be "just engineering" it will be an engineering wonder. I have run the numbers. It will be very tough. I'm not worried about alpha impingement. As you point out that will be a small problem. It is the heat load that will be a killer.
Yow. Put that way, it sounds insurmountable even if Dr. B was right on the physics.MSimon wrote:Dr. Mike,
I'm 99% sure the physics will work out because every doubt I had on that score has been corroborated by independent sources. I believe Dr. B played it totally straight.
Dr. B thought the intercept area on a 100 MW reactor would be 20%. That is 20 MW. To say that it is "just engineering" underestimates the difficulties. You have to draw off that 20 MW within 3" or less of 4 Deg K.
It will not be "just engineering" it will be an engineering wonder. I have run the numbers. It will be very tough. I'm not worried about alpha impingement. As you point out that will be a small problem. It is the heat load that will be a killer.
There are things you can do. Making the reactor bigger for a given power out is one. Not the best one (for reasons of economics) but, you could do it.Yow. Put that way, it sounds insurmountable even if Dr. B was right on the physics.
The core problem (because of vacuum insulation) is radiation. Silvering (or aluminization, or gold coating etc.) of the inside of the pipes is one thing that will help.
The use of an aneutronic fuel is probably essential.
Another thing that would help is high T (relatively) superconductors. Being able to run the superconductors at 20K vs. 4K would be a huge advantage. MgB superconductors are probably the way to go until better materials are available.
We do have enough tricks to get past the difficulties. The question is: after all the tricks will the power be economical?
The essence of engineering is: economics meets physics/chemistry/available materials and production methods. What have you got? What can you make? Will it meet economic goals?
I agree with you Simon. But solving challenging problems is what makes engineering fun.
The SR-71 was "just engineering". They only had to invent several materials and develop
new engines. It was so amazing for its time it was kept secret to the people who paid for it.
I think we can overcome the engineering challenges. We may be able to use liquid nitrogen superconductors, that's 77K, almost a 20 fold improvement from 4K. Inventing that for this problem would help solve a lot of other problems for a lot of other purposes.
If the physics works, I can build it! That's just engineering attitude.
The SR-71 was "just engineering". They only had to invent several materials and develop
new engines. It was so amazing for its time it was kept secret to the people who paid for it.
I think we can overcome the engineering challenges. We may be able to use liquid nitrogen superconductors, that's 77K, almost a 20 fold improvement from 4K. Inventing that for this problem would help solve a lot of other problems for a lot of other purposes.
If the physics works, I can build it! That's just engineering attitude.