Best method for direct energy conversion?

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Sven Andersson
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Best method for direct energy conversion?

Post by Sven Andersson »

I have a question about direct energy conversion; if I want to directly extract electrical energy from a fusion reaction that occurs in a relatively cold plasma and which generates charged particles, like He nuclei, with an energy in excess of 1 MeV, what is the most suitable method of doing that?

This is how it will look like; the fusion reactions occur in a plasma (that may be magnetically confined) and the He nuclei shoot away at very high speed, leaving a plasma with excess electrons behind.

Should some method with charge separation be used or perhaps some method with magnetic fields, like the inverse cyclotron converter, of Tri Alpha Energy?

Sven
John Fenley
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Re: Best method for direct energy conversion?

Post by John Fenley »

Check out the atomic battery page at wikipedia. I think the direct charging generator would be a good option for you.

http://en.wikipedia.org/wiki/Atomic_bat ... generators
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Richard Hull
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Re: Best method for direct energy conversion?

Post by Richard Hull »

The only thing you need to make a great, powerful direct charging generator is several tens of thousands of curies of some kind of radioactive isotope. A real snap. I am amazed no one here has put one together yet. Oh, maybe they have and died a few days later.

There is absolutely no nuclear energy solution for the amateur at any level, at any point, by any artifce in any future time.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Bob Reite
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Re: Best method for direct energy conversion?

Post by Bob Reite »

A real SNAP! LOL (for those that don't remember, that was a 1960's experimental reactor for use in space. SNAP stood for Systems Nuclear Auxiliary Power.)
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Richard Hull
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Re: Best method for direct energy conversion?

Post by Richard Hull »

The SNAP series of which there were about 15 or more different models and variants were all RTGs (Radioisotope Thermoelectric Generators) and used the decay heat, (particle kinetic energy to heat) of deadly amounts of radioisotopes to heat simple electric thermocouples and generate power. The voyager and pioneer missions in the 70s used the best of these SNAP RTGs for their long mission power. The first little SNAP1 was used to power a tape recording of President Eisenhower's address from space in the late 50's.

There was no direct conversion of the charged particles to electricity, of course, in any spacecraft.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: Best method for direct energy conversion?

Post by Dennis P Brown »

One method to convert any plasma directly into electrical current is MHD (Magneto-hydro-dynamics) conversion. MHD power generation is rather simple - see https://en.wikipedia.org/wiki/Magnetohy ... _generator

That said, not always useful for some approaches. People have built coal fired units and used MHD to get electricity directly avoiding turbines (MHD can convert up to 90% of the available energy into electricity) but erosion issues in the MHD system made it impossible for practical power plants. A fusion reactor (of the correct type) could use this but the issue is to extract the required plasma without disrupting the field or remaining plasma - generally not worth the effort with massive neutron flux available to tap.

An aside: always wondered why a simple magnetic mirror fusion machine was never built with MHD generators at each mirror end. In this manner, most all the lost energy that leaks through the magnetic mirror ends of the machine could be recovered. Since the axial field between the magnetic mirrors easily contain a stable fusion plasma but only losses at the mirrors made them impractical wondered why this solution was never tried. I'd think the gain of a fusion machine would be ample for a 20% loss rate ... guess not.
Dan Tibbets
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Re: Best method for direct energy conversion?

Post by Dan Tibbets »

Direct conversion is a poorly defined criteria. If you use a steam cycle of thermal power it may be indirect or thermal conversion. A thermocouple in this case might be considered direct conversion. The conversion of the KE of charged particles is somewhat different. Electrostatic fields can in principle do this easily. In practice it is another story. I do think that some vacuum tube amplifiers do this directly.
The first requirement for direct conversion of the KE of charged particles is separating them from the reaction space. This might be in a method proposed for the Polywell, or the Dense Plasma Focus. In an ignition machine the KE of the fusion produced charged particles are used to heat the plasma so direct conversion is limited, though in a pulsed machine like the DPF it may be possible.

The two ways I know of involve either electrostatic deceleration or pulsed MHD effects (?). Add to this methods for capturing the KE of some sub components of the energy output. This would be X-ray conversion via photovoltaic approaches like that proposed and patented by the DPF folks. IF this can be made to work at high efficiencies, it may be very important for advanced fuels like P-B11 fusion. The Bremsstruhlung X-ray radiation may otherwise be a show stopper.

It is important to remember that even with high efficiency direct conversion of fusion produced charged particles, the thermal heat load from lost energy- Bremsstruhlung, other radiation, particle confinement escape , etc.will be considerable and heroic efforts at cooling may be needed. The question is not so much thermal versus direct conversion, but the efficiencies and cost of the two approaches. Steam thermal cycles may limit efficiencies to ~ 25-50% (for super critical CO2 ). For additional gains or substitute gains from direct conversion, if net conversion efficiency can be pushed to 70-90%, the picture changes somewhat.Cooling, while still required, may not need a steam cycle for energy conversion. This eases things in a number of ways. Of course if the direct conversion adds disproportionate complexity and cost nothing has been gained in the final profit equation. Even if an imaginary plant produced electrical power at a conversion efficiency of 90% of the total input and output energy combined that would still leave 10% heat that has to be handled. A 1 GW energy producing plant may be producing 100 MW of unavoidable heat. Active cooling will still be needed. An example: a reactor requires 100 MW of input energy (ends up as waste heat) , 1 GW of fusion energy is produced (Q of 10). If 90% of the fusion energy is direct converted, this leaves a remaining additional 100 MW of heat energy. That is 200 MW of waste energy that has to be dumped into the environment. If it is passed through a steam cycle perhaps 50 MW of this heat energy may be added to the electrical output, leaving 150 MW of waste heat to be dealt with. This analysis can be skewed to various assumptions, and the bottom line is always a compromise cost benefit ratio. Even a fusion reactor with a Q of less than one could produce a profit, if your conversion methods are efficient enough. Even an amateur fusor could theoretically be energy profitable, all you need is a net conversion of thermal energy and /or charged particle KE that is about 99.9999999 % efficient. You could even have enough surplus electrical energy to power a 10 Watt light bulb if you strung about 100,000 fusors together. Lets see, the cost per KW hour might be around a 100 billion dollars. Add the costs of the stupendously efficient conversion apparatus and the final cost might be above a trillion dollars per KWh. That probably would not compete well with a coal fired power plant, or an ant powered treadmill. Efficiency of the reactor (Q), and efficiency of conversion are important, but so is the energy density. This is a tremendous challenge for Tokamaks, even if the physics can be made to work. To get useful amounts of electricity you have to build a very huge and expensive plant.

Also, keep in mind that the end product does not need to be entirely electricity. The heat, which might otherwise be considered as lost waste could be used in chemical plants, or to heat buildings, etc. without going through a conversion to electricity step.

Dan Tibbets
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Richard Hull
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Re: Best method for direct energy conversion?

Post by Richard Hull »

Dan is wise to include the economics as that is the bottom line as to whether you, personally, or the world will ever see the first watt of fusion generated electricity flow out of a wall outlet. Forget the supposed reality of doing efficient fusion, (still a dream), forget the enegineering required or the massive size of any fusion plant. If it ain't very, very profitable, it will never be. Money will determine fusion's future not the science or the human condition or needs.

Some wide eyed folks who show up here are like a newborn, you have to slap them to bring them into the real world. The womb was warm, comfortable and an ideal environment. However, we are now part of the real world and crying is our first real world effort followed by more as we age. Wisdom and the reality of things comes to us through exposure and experience.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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