[JimmyT]

Eric’s term “plasmoid” actually refers to the tiny ball made of plasma filaments.

Plasma, except perhaps for jets. must be electrically neutral. That is it must contain a roughly equivalent number on protons in its constituent nuclei, and electrons either bound or free. At these high energies they are all free.

The beam is not a direct result of the fusion reactions. It is a result of the collapsing magnetic field which is confining the plasma which makes the plasmoid. This collapsing field accelerates the electrons in the plasma in the opposite direction as the nuclei. The fusion reactions in turn fuel the magnetic field. I’m not sure we understand how exactly. Eric might.

As to the electron’s energy, Eric believes that in the process of spiraling around in the filaments which make up the plasmoid; they will transfer most of their momentum to the helium nuclei.

[JimmyT]

Thorium breeder reactors will never be able to compete cost-wise with power production by focus fusion. Not by several orders of magnitude.
But molten salt thorium reactors can use high level nuclear waste as part of their fuel supply. Producing power from it, not consuming power to destroy it.

There is lots of material on-line about molten salt nuclear reactors

[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?

[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?

[JimmyT]

Henning wrote: Patrick: I think your proposal was ignored, because it was similar to Eric’s initial idea of using a diamond/laser switch. Diamonds are insulators, but conduct pretty well when ultra violet light is shined upon. This was considered to be too expensive, and no-one ever built a switch that big. So Eric and Murali fell back to ionizing spark plug switches (don’t know if it’s the right name). But what you’re now proposing is something different.

patentable?

[JimmyT]

Ivy, you are right a Babbage machine was never built in his lifetime. But one was constructed in 2002!

http://www.computerhistory.org/babbage

Hmm, can’t get this to link.

[JimmyT]

Tulse, I was thinking something similar. But this is getting pretty close to the defination of theoretical break even. I wonder if we should just be happy with an adequate defination of that term.

[JimmyT]

Rezwan wrote: Folks, I want to put together something to explain the objective/deliverable of fusion research.

Looking up Q, we see:

The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state.

How does this relate to LPPX’s DPF?

Similar discussion at this thread. Mergeable?

This definition doesn’t work very well with the DPF process. Since DPF’s are never really in a steady state. I wonder if some alternative definition would work better ?

[JimmyT]

Allan Brewer wrote:

Wont the speediest ones come out, first?
Let’s design the system to allow the particle velocities to stratify.

The effective coil length would then change through the duration of the exit beam.

JimmyT wrote:
What I wrote is, of course, a bit of a simplification. The field strength of the coil is not constant, but will increase as particles deposit their energy there. And some slower particles will likely come before some faster particles. But the ideal particle speed distribution is exactly the opposite of what stratification would create. You would like the slowest particles first with a gradual increase in speed as the coil’s field strength increases. Unless we are extremely fortunate nature will not be so cooperative.

Lets say the distance from the site of plasmoid annihilation to the Rogowski coil is 1 metre. A 65KeV He ion travels that distance in about half a microsecond. If the duration of the plasmoid annihilation is very much less than one microsecond (is it??), (and we know the plasmoid is extremely small compared with a metre), then the Helium ions will indeed arrive at the coil smoothly graded fastest first and slowest last. If the coil is optimally designed, we could envisage the fast ion being slowing to a halt in the coil before slower ions even reached the coil, or alternatively that the fast ion spends longer in the coil than the slower ion such that they all grind to a halt at about the same time.

The more I think about this the more convinced that the optimal solution is only going to be found by running simulations. There are just too many variables to figure out the best solution.

[JimmyT]

vansig wrote:

Let’s say you design your system to go after particles of 65Kev and were able to capture all the energy from them. Any particles of energy less than that would be decelerated, stopped and reversed by the induced magnetic field. Accelerating them back into the reaction chamber and taking some energy with them. Any particles faster than that will still have their residual velocity (the amount in excess of 65Kev ) when they reach the helium catchment container (Which thus may need cooling.)

Wont the speediest ones come out, first?
Let’s design the system to allow the particle velocities to stratify.

The effective coil length would then change through the duration of the exit beam.

What I wrote is, of course, a bit of a simplification. The field strength of the coil is not constant, but will increase as particles deposit their energy there. And some slower particles will likely come before some faster particles. But the ideal particle speed distribution is exactly the opposite of what stratification would create. You would like the slowest particles first with a gradual increase in speed as the coil’s field strength increases. Unless we are extremely fortunate nature will not be so cooperative.

[JimmyT]

zapkitty wrote: At this time the classic dimensions of the “box” still seem to be holding… 1 x 4 x 9… errr… I mean 2m x 2m x 3m…

As I understand it that volume should include the DPF in its vacuum containment, the alpha power takeoff gear, the caps and switches and other electronics directly involved in the DPF cycle, an “onion” of indeterminate thickness and any power circuitry that’s part of it, the heat rejection gear to transfer the heat of all of the above out of the box and a roughly spherical volume of water about a meter in radius surrounded by a shell of other materials a few centimeters thick.

Outside the box there is presumed to be an external power feed to prime the caps and the cooling gear to handle the heat rejected from the box.

So what have I missed that needs to be in the box?

And what have I missed that that is required by an FF DPF but does not necessarily need to be in the box itself?

Cooling tower, or heat exchanger with lake water discharge, or dry cooling unit (3 times as big as the wet one) or some combination of these, and associated pumps. Transformers to adjust electricity to needed voltage(s).
None of these need to be or, in some cases can be, in the box.

[JimmyT]

Allan Brewer wrote:

…

Its still correct however that assuming the expected 10-20% inefficiency there would be 4-8MWatts of heat to remove from the system – which is challenging – its just that the heat is not arising from electrode resistance.

I’m curious what inefficiencies you envisage. Heat is directly generated in the plasmoid, and some losses would be expected in the ‘onion’. What others do you see?

Well that’s really the question I have been asking during this thread. I started with Rezwan’s posting https://focusfusion.org/index.php/site/article/how_will_we_get_there_from_here/ which not unreasonably expects unspecified inefficiencies of that order. I suspect you are right that the 70KJoules of energy to form the plasmoid will not all come out with the fusion energy into the Rogowski coil, and the onion will be less than completely efficient capturing the X-rays’ energy.

The problem of efficient energy capture from the ion beam is pretty fundamental. We are not sure what the velocity distribution of the ions is going to look like. The best guess is a Boltzman distribution. At any rate, the particles are not all going to be traveling the same speed. You must design the system to capture the maximum energy … But…

Let’s say you design your system to go after particles of 65Kev and were able to capture all the energy from them. Any particles of energy less than that would be decelerated, stopped and reversed by the induced magnetic field. Accelerating them back into the reaction chamber and taking some energy with them. Any particles faster than that will still have their residual velocity (the amount in excess of 65Kev ) when they reach the helium catchment container (Which thus may need cooling.)

There may be a way to mitigate this problem by using multiple coils. But I’m not sure how we would do that exactly.

We can hope that the velocity distribution is more uniform than a Boltzman distribution, which would make energy extraction more efficient. And the recent insights into plasma heating mechanisms may support that.

[JimmyT]

One factor working against a world wide focus fusion powered air distribution network is this: Conventional freight transport isn’t going to stand still either. Ships will be cheaper to operate and undoubtedly cruse faster, since fuel costs won’t be so important. Rail transport will experience some savings for the same reason (fuel costs, not speed). So there will be a new baseline to compete against.

I think upgraded rail and ports will probably make more sense.

[JimmyT]

zapkitty wrote:

This subject of servicing the generator units has bothered me a lot. How to provide uninterupted power to communities or factories which are widely dispersed?

Solution 1: Maintain an interconnecting grid to provide power when units are down.
This strikes me as a terribly inefficient use of resources. Maintaining a grid for use only a few hours each year.

Solution 2. Have duplicate generator units at each station. Or alternatively place units where power demands dictate the placement of two or more units. Then, service them during off-peak hours.
Again, idle units are a waste of capital, and would be intolerable until the market is virtually saturated.

Comments? This post probably doesn’t belong here. New thread maybe?

The current practical solution would be a combination of 1 and 2.

Communities and large installations such as factories and hospitals will demand
backup units… and the low price of DPF units will make that option especially attractive.

And the grid will retain its current extents for the same reason it currently exists… shifting
power to where it’s needed while buying and selling power produced in excess of local needs.

Another way of thinking of this is that the ready availability of cheap, clean power will
in no way reduce the current demands for power generation and its transport.

Will there be changes in the grid structure? Yes. But DPF by itself will not render the
concept of the grid obsolete.

I actually think that it might. It may well become cheaper to generate more power where it’s needed then to maintain the infrastructure to transport it.

I’m no expert in failure analysis, but I have a sense that grids may at some point decrease reliability.

[JimmyT]

This subject of servicing the generator units has bothered me a lot. How to provide uninterrupted power to communities or factories which are widely dispersed?

Solution 1: Maintain an interconnecting grid to provide power when units are down.
This strikes me as a terribly inefficient use of resources. Maintaining a grid for use only a few hours each year.

Solution 2. Have duplicate generator units at each station. Or alternatively place units where power demands dictate the placement of two or more units. Then, service them individually during off-peak hours.
Again, idle units are a waste of capital, and would be intolerable until the market is virtually saturated.

Solution 3:Mobile focus fusion unit on service truck. Drive unit to proximity of unit being serviced. Quick connect electricty and cooling. Switch on. Switch off unit being serviced. Wait 9 hours. Service other unit. Restart unit. Switch mobile unit off. Disconnect mobile unit. Drive to next unit scheduled for service. Shielding water could be kept on site, thus needn’t be transported.

Solution 4: Same as #3 except you drive off with the “hot unit” rather than wait around for it to “cool off”. Only downside to this is that you would be transporting some mildly radioactive material. On the plus side: generators could be serviced at a central location where specialized equipment could be available. Serviced unit could be ready for redeployment the following day.

Comments? This post probably doesn’t belong here. New thread maybe?

[Author]

Posts