Dr. Mike,
77K superconductors are no panacea.
The stronger the magnetic field the more you have to cool them to maintain superconductivity.
20K seems like the best we can do now for the strength of fields we want to use.
Details On The WB-7 Experiments
Liquid helium cooling is going to instantly negate any other advantages you have if only for economic reasons. Plus, helium is starting to run in short supply. (Yes, that would be self-correcting if you had a working boron-proton fusion device, but that gets ahead of the situation.)MSimon wrote: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.
LHe cooling is only a difficulty if you don't recycle the He. In fact most all commercial users of LHe (think MRIs) recycle the He.Liquid helium cooling is going to instantly negate any other advantages you have if only for economic reasons. Plus, helium is starting to run in short supply. (Yes, that would be self-correcting if you had a working boron-proton fusion device, but that gets ahead of the situation.)
BTW most all proposed fusion devices produce He4 as an endpoint, because He4 is anomalous with respect to binding energy i.e. very favorable.
A 100 MW (D-D or pBj) reactor will produce about .5 Kg a day of He4. A couple of weeks operation should be sufficient to collect enough He4 for the next reactor. At most a few months should do it.
But LN2 is so much cheaper!! If we can run on LN2 instead of LHe it would save a *lot* of cash. Plus, radiant energy transfer goes as the 4th power of the temp difference, even a little bit of change in delta-T goes a long way in energy savings.
I think trying for 77K is worth the effort for production level plants. Creating the magnets is not yet possible, but this might put a fire to the research (like more cash, same story every where!)
Getting a large WB to work with LHe is fine for a prototype. But I think we will need to reduce costs a lot for production units and going with LN2 will help there.
I think trying for 77K is worth the effort for production level plants. Creating the magnets is not yet possible, but this might put a fire to the research (like more cash, same story every where!)
Getting a large WB to work with LHe is fine for a prototype. But I think we will need to reduce costs a lot for production units and going with LN2 will help there.
Dr. Mike,drmike wrote:But LN2 is so much cheaper!! If we can run on LN2 instead of LHe it would save a *lot* of cash. Plus, radiant energy transfer goes as the 4th power of the temp difference, even a little bit of change in delta-T goes a long way in energy savings.
I think trying for 77K is worth the effort for production level plants. Creating the magnets is not yet possible, but this might put a fire to the research (like more cash, same story every where!)
Getting a large WB to work with LHe is fine for a prototype. But I think we will need to reduce costs a lot for production units and going with LN2 will help there.
All I ask for is a production super conductor (say in 1 to 5 Km lengths) that will support 1 to 2 T at 77K.
Right now such a material is as scarce as unobtanium.
Note: the MRI guys use LHe with sterling cycle re-liquifiers. I personally think MRI technology would be fine for the initial production.
We might be able to go higher than 20K for MgB
http://iecfusiontech.blogspot.com/2007/ ... ances.html
In any case the real killer is not the LHe LN2 interface. The MRI guys do that OK. The Killer is the 650K boiling water/LN2 interface.
A possibility is adding another layer of water at 300K.
Rube Goldberg would be proud.
I think the complexity of any fusion reactor makes that a fact!Rube Goldberg would be proud.
But if we can invent high Tc superconductors along the way, it's a bonus.
You get no argument from me about the delta-T. I've been trying to point
that out to the Tokamak folks for a couple of decades. Plus the neutron flux is a killer. Quite literally. The challenge is what makes it fun!
Question, is there a potential method of using an inner/shielding coil? Perhaps a smaller series of coils built with a non conductive material with a non pressurized coolant (molten salts?) to intercept a good portion of the collision prone 20% of the beta particles.
I'm not sure how practical such a configuration would be or if there'd even be enough space available. It seems though if you could intercept the majority of those particles, which would have struck the coil housings, the engineering might not have to be so extreme. Would such a thing be possible, in a full scale design, without interfering with electron confinement?
Additional point. Didn't the people looking into the levitated dipole concept have problems of a similar nature?
I'm not sure how practical such a configuration would be or if there'd even be enough space available. It seems though if you could intercept the majority of those particles, which would have struck the coil housings, the engineering might not have to be so extreme. Would such a thing be possible, in a full scale design, without interfering with electron confinement?
Additional point. Didn't the people looking into the levitated dipole concept have problems of a similar nature?
Absorbing the alpha energy with the outer sheath of the coil is no problem. The problem is the energy deposited.JD wrote:Question, is there a potential method of using an inner/shielding coil? Perhaps a smaller series of coils built with a non conductive material with a non pressurized coolant (molten salts?) to intercept a good portion of the collision prone 20% of the beta particles.
I'm not sure how practical such a configuration would be or if there'd even be enough space available. It seems though if you could intercept the majority of those particles, which would have struck the coil housings, the engineering might not have to be so extreme. Would such a thing be possible, in a full scale design, without interfering with electron confinement?
Additional point. Didn't the people looking into the levitated dipole concept have problems of a similar nature?
As Dr. Mike points out this will have to be extreme engineering (well, extreme until it becomes common place). That's where the fun is. :-)
http://www.youtube.com/watch?v=HbsXLzDwg6Q
I'm not very familiar with the levitated dipole concept. Got a link?
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Levitated Dipole experiment...
http://psfcwww2.psfc.mit.edu/ldx/
It's plasma confinement but seems a bit more elegant than tokamak. Not sure how practical it is though.
As to the rest well yes I agree, energy transport is the problem. Perhaps if it was broke down into different solutions paths the engineering would be easier (i.e. instead of trying to design the primary coil housings to handle all environmental parameters). Just thinking out loud.
http://psfcwww2.psfc.mit.edu/ldx/
It's plasma confinement but seems a bit more elegant than tokamak. Not sure how practical it is though.
As to the rest well yes I agree, energy transport is the problem. Perhaps if it was broke down into different solutions paths the engineering would be easier (i.e. instead of trying to design the primary coil housings to handle all environmental parameters). Just thinking out loud.
There is no way to get around the necessity to make the coils capable of handling their environment.JD wrote:As to the rest well yes I agree, energy transport is the problem. Perhaps if it was broke down into different solutions paths the engineering would be easier (i.e. instead of trying to design the primary coil housings to handle all environmental parameters). Just thinking out loud.
Any shield would have to handle the environment plus keep the electrons at bay. So you are back to the place you started from.
BTW the levitated Dipole looks like a research project not a design for a functional reactor.
Proof of concept. Not sure what their funding status is these days. The reason I mentioned this earlier though, consider the environment the levitated, superconductor ring would be nested in. Perhaps some initial thoughts on design by them might be applicable.BTW the levitated Dipole looks like a research project not a design for a functional reactor.
Whether the levitated dipole actually works or not isn't the issue. I raised the point as a possible place to look for concepts of design. They're trying to use a superconductor within an area containing highly energetic particles. Considering the slant of this thread I thought it might be of some value as far as concepts. I'm not arguing for the levitated dipole as a competitor to the Bussard concept.
Stored cold is not a useful concept for dissipating 20 MW in a running reactor.
Unless the plan is to run the reactor for 5 or 10 - 1 sec pulses in a 10 hour period.
In any case even 20 MJ for 1 second is likely to cause a superconductor explosion from stored magnetic energy.
There is not going to be some magic bullet. We are going to have to extract the energy at around 600 deg K and keep the magnets below 20K. That is just a fact of life. It can be done (I'm convinced) it will just require some tricks - like an extra layer of coolant at 300K.
The tough part will be getting all that squeezed in the right form factor.
Let me add that I do not in any way wish to discourage you from thinking of other concepts that might help. I will continue to raise objections (if I have any) until we come up with a good idea.
Science is hard. Engineering is harder.
I always wanted to be a scientist when I grew up. I kind of fell into engineering. I think I like it better. The problems are harder.
We are most fortunate that Dr. B was more of an engineer than a scientist. I'm sure he contemplated these problems and factored them into his research.
Unless the plan is to run the reactor for 5 or 10 - 1 sec pulses in a 10 hour period.
In any case even 20 MJ for 1 second is likely to cause a superconductor explosion from stored magnetic energy.
There is not going to be some magic bullet. We are going to have to extract the energy at around 600 deg K and keep the magnets below 20K. That is just a fact of life. It can be done (I'm convinced) it will just require some tricks - like an extra layer of coolant at 300K.
The tough part will be getting all that squeezed in the right form factor.
Let me add that I do not in any way wish to discourage you from thinking of other concepts that might help. I will continue to raise objections (if I have any) until we come up with a good idea.
Science is hard. Engineering is harder.
I always wanted to be a scientist when I grew up. I kind of fell into engineering. I think I like it better. The problems are harder.
We are most fortunate that Dr. B was more of an engineer than a scientist. I'm sure he contemplated these problems and factored them into his research.
Magnetic Dipole Experiment
I like that the Megnetic Dipole reflects thinking outside the "mimic Nuclear Weapons" box. The Magnetic lines converge in the center, rendering this experiment as a more non-isotrophic experiment.
They're beginning to look at the possibilities of not requiring the whole plasma to be the same tempurature.
It seems though, like 99% of the rest of the Fusion community, they're in it for the science at their first objective. It still seems like design supporting science instead of science supporting design.
They're beginning to look at the possibilities of not requiring the whole plasma to be the same tempurature.
It seems though, like 99% of the rest of the Fusion community, they're in it for the science at their first objective. It still seems like design supporting science instead of science supporting design.