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 Post subject: Lftr/MTF hybrid
PostPosted: Dec 25, 2008 10:02 pm 
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Lftr/MTF hybrid - The following is an Lftr adaptation proposal describing a variation of the Acoustically Driven Magnetic target fusion MTF technology from General Fusion Inc.

Resource:

http://www.generalfusion.com/files/evidence.pdf

<snip>

Background

Magnetic target fusion (MTF) is a new fusion regime presently being studied by many researchers. Normal magnetic fusion operates at a plasma density of around 10**14 cm-3 and needs a confinement time of ~1 s to achieve energy gain. This turned out to be difficult because of plasma instabilities. The inertial approach seeks a density of 10**25 cm-3 and requires a confinement time of 1 ns. They are facing difficulties with the stability of the implosion and the extreme power requirement of the driver. MTF is an intermediate concept requiring density of ~10**20 cm-3 and a confinement time of 1 us. Because the pressure of plasma of this density at thermonuclear relevant temperature is ~1 Mbar, only a pulsed machine can generate these pressures.


The MTF approach consists of producing cold, low density plasma and rapidly compressing it to thermonuclear conditions. Because of the much reduced confinement time compared to magnetic fusion, the reduced plasma lifetime due to plasma instabilities is now acceptable. Also the energy required to compress the plasma is delivered in a much longer time than the inertial approach, reducing the power and complexity of the driver.

Proposal

The Lftr/MFT hybrid proposes a new plasma compression system that offers many advantages. A tungsten near spherical vessel ~2 m in diameter is filled with subcritical mixture of thorium fluoride (used to breed fuel), beryllium fluoride (used to slow fast neutrons and create multiple neutrons from alpha particles and fast neutrons), and enriched uranium fluoride (used to keep the salt warm) fuel to provide just enough heat to keep the core salt in a liquid state.


The core salt is spun in the vessel by core salt circulator pumps that inject the liquid tangentially near the equator and pumps it out near the poles. These pumps also feed the primary core salt heat exchangers to transfer reactor core heat to the turboelectric generators. This creates a vertical vortex tube in the core salt. The vessel is surrounded by many electronically actuated pistons. Microprocessor controlled linear electric motors accelerate the pistons to ~100 m/s. The pistons impact the spherical tungsten core vessel and send a strong acoustic wave into the core salt.

The pressure developed at the impact is: P=pvcs/2 where p is the density, v the speed of impact and cs is the sound speed in the impacting material. For tungsten p =19250 kg/m3 and cs=4290 m/s so the pressure developed is about 4 GPa. This is about twice the pressure specified by General Fusion Inc.

The wave then focuses in the center, getting stronger. Just prior to the wave collapsing the center vortex, a computer controlled plasma generator forms two spheromaks (a toroidal magnetized plasma configuration) of reverse helicity that are injected from the top and bottom of the core sphere. They move rapidly to the sphere center where they merge to produce a stationary FRC (Field Reverse Configuration). The advantages of this plasma target are that it can be rapidly sent in the center just prior to collapse and then stay there with low velocity while the vortex collapses and compresses it. The toroidal magnetic field is canceled and its energy goes into thermal energy heating up the plasma just prior to compression.

Also, it has been observed that when merging, the resulting plasma has higher ion temperature than electron temperature. As radiation losses increase with electron temperature but fusion goes with ion temperature, this may somewhat improve the operation. After compression, 20% of the heat flows into the core salt and the remaining 80 % of the fusion energy is released in 2 to 14 MeV D-D, D-T, T-T fusion neutrons and alpha particals contributing in the fission reaction of the core salt. The cycle is repeated at ~1 Hz.

This cycle time can be thermostatically adjusted by the control computer to maintain the core salt temperature at an optimum level reactive to changes in external power demand either increasing or decreasing. Another computer controlled thermostatically adjusted variable is the isotopic composition of the core salt as the salt chemistry can vary over time.

Heat transients can also be automatically mitigated by adjustment in the fusion cycle time.

Since the core salt is maintained at a subcritical level, no freeze plug of dump tanks are required since cessation of the cycle stops the fusion/fission reactions.


Because of the high accuracy of the impact timing of the numerous pistons (~1 us), an electronic means of controlling the exact piston trajectory is required.

In particular, the acoustic system does not require any high electrical power components. The microprocessor controlled pistons are coordinated by sensors along the path of the piston runway to achieve the required velocity and simultaneous impact time. Any acoustic wave shaping can be achieved by microprocessor firmware to compensate for core salt temperature and density variations.



The spheromak generator will use a pulse power electrical system. But as only ~1% of the compression energy is required for the initial plasma, this should be only a 1 MJ system worth ~3 M$.

Most neutrons and all other radiations are absorbed in the thorium, uranium, and beryllium fluoride salt in the ~1 m radius of core salt so the neutron flux at the wall is minimized.

This is extremely advantageous over many other fusion systems where neutron and radiation wall loading is a difficult and mostly unresolved technical issue. Radio isotopes waste produced by neutrons is eventually removed by Lftr salt reprocessing. Achieving fusion break-even is not required since most of the thermal energy is derived from fission.

The surplus neutrons produced by acoustic fusion plasma compression will enable complete burnup of all high level transuranic waste isotopes.

A thorium blanket can also absorb waste neutrons as in other Lftr configurations. In this configuration the acoustic generator located on the outside wall of the blanket, sends the acoustic pulse through the blanket, then the core barrier, into the core salt to condense the plasma at the center of the core.

How it works

1. The impact of the pistons sends a compression wave reverberating through the core salt and toward the the plasma suspended by a magnetic field in the center.

Image

2. The compression wave picks up speed as it hurtles toward the center, quickly becoming a shock wave powerful enough to compress the plasma quickly and violently.

Image

3. The shock wave hits the plasma, a highly energetic stew of the hydrogen isotopes "tritium and deuterium" (T-D) or "deuterium and deuterium" (D-D). The force is so great that the ions merge to form helium.

Image


4. The fusion reaction hurls neutrons and alpha particles out through the core salt, creating heat in the core salt to power an electricity-producing turbine.

Image


General fusion

http://link.brightcove.com/services/link/bcpid3924348001/bctid5659122001

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 26, 2008 8:55 am 
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So now instead of the fission device being turned into a power plant, you're trying to turn a fission-fusion device into a powerplant? Well, at least u238 will fission when smacked by those energetic neutrons.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 26, 2008 9:59 pm 
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fnord wrote:
So now instead of the fission device being turned into a power plant, you're trying to turn a fission-fusion device into a powerplant? Well, at least u238 will fission when smacked by those energetic neutrons.



They say that you should always put your best foot forward.

This wisdom was first recorded in 1613 from Sir Thomas Overbury: "Hee is still setting the best foot forward."

Even though the Lftr is mostly an Lftr reactor, it is good spin to turn it into a fusion reactor because of the positive connotations that fusion has over fission. The following is an exercise in nuclear spin.


In the four cardinal themes of the nuclear debate; Nuclear Security, Proliferation, Waste, and Safety the Lftr fusor is without peer among those systems whose designs that we have so far discussed.

First take inherent safety. Because it is sub-critical, any anomaly in reactor operation will immediately result in a power shutoff to the acoustic generator affecting an instant shut down of the fission/fusion reaction. The large volume of core and blanket salt will absorb any decay heat that is produced by background fission activity. Because of its very low fuel enrichment levels, this waste heat potential is the lowest among possible Lftr configurations.

Then there is the question of nuclear waste. Because only non transuranic waste is removed form the Lftr fusor by a totally automated core salt reprocessing regime, that very small quantity of resultant waste need only be stored for a few hundred years at the reactor site before it degrades to a benign radiation level. Once radiation free, this material can enter the raw material stream of industry.

A mixture of uranium salts are also removed during core salt reprocessing to keep the Lftr fusor subcritical. These salts will be utilized by small unattended Lftr nuclear batteries in third world countries that lack an extensive electricity power or industrial heat infrastructure.

Because the Lftr fusor operates within a few degrees of 1000C, it can generate hydrogen or electric with efficiency in the mid 50% range.

The current inventory of light water reactor wastes and weapons material can also be burnt in the Lftr fusor. Once sufficiently diluted to maintain sub-criticality, the Lftr fusor can extract every last watt of energy that has been previously wasted by older and less competent reactor generations.

As for Proliferation, The trace amounts of Plutonium that the Lftr fusor produces never leaves the core salt and is burned by the fusion process completely out of existence. There is absolutely no opportunity for transuranic isotope diversion to the proliferators.

Because of its air cooled operation, its radioactive and corrosive core salt, and its hardened underground deployment only industrial levels of security are needed to protect the Lftr fusor.

The Lftr fusor is a simple, inexpensive, compact, and rugged machine. Because of the quality of it materials and simplicity of design, it is easy to maintain. It is factory buildable with all the advantages that mode of production affords,

In summary, the Lftr fusor is the most cost effective, efficient, safe, proliferation resistant and clean power source on the energy production scene today.

The preceding was an exercise in nuclear spin.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 26, 2008 10:49 pm 
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Quote:
The Lftr fusor is a simple, inexpensive, compact, and rugged machine. Because of the quality of it materials and simplicity of design, it is easy to maintain. It is factory buildable with all the advantages that mode of production affords,

In summary, the Lftr fusor is the most cost effective, efficient, safe, proliferation resistant and clean power source on the energy production scene today.

The preceding was an exercise in nuclear spin.


So is that last sentence supposed to be the punchline showing this was all a joke? If you are actually asking for this to be taking seriously can I at least ask that you refrain from using such statements of 100% confidence about simplest, cheapest most stupendous that you seem to not be able to resist with each new thought.

David L.


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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 27, 2008 12:08 am 
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David wrote:
Quote:
The Lftr fusor is a simple, inexpensive, compact, and rugged machine. Because of the quality of it materials and simplicity of design, it is easy to maintain. It is factory buildable with all the advantages that mode of production affords,

In summary, the Lftr fusor is the most cost effective, efficient, safe, proliferation resistant and clean power source on the energy production scene today.

The preceding was an exercise in nuclear spin.


So is that last sentence supposed to be the punchline showing this was all a joke? If you are actually asking for this to be taking seriously can I at least ask that you refrain from using such statements of 100% confidence about simplest, cheapest most stupendous that you seem to not be able to resist with each new thought.

David L.



In the thread: "Proliferation Resistance and Nuclear Power" where we compared the proliferation resistance of various nuclear fuels, it became apparent to me that the perceived proliferation resistance of TRISO fuel was a prevarication. But that perception has catapulted the PBMR into the forefront of the future of nuclear power. Clearly with your help I now see behind this ill deserved reputation of TRISO fuel and those systems that use it as a very successful and masterful exercise in propaganda. That said, now I greatly admire the skill implicate and self evident in the TRISO/PBMR spin campaign having been fooled by it completely and totally for so many years.

The narrative of that “Proliferation Resistance” thread roiled in confusion by the intermingling of spin and fact. The various and sundry concepts there dealt with flashed back and forth between fact and perception were challenged in a great effort to understand the true principles of reality in those questions at hand. But that struggle wrought a new enlightenment on my part thanks to your deeply appreciated mentoring and guidance. So I decided in this thread to state up front that I was dealing in a sales exercise to eliminate any possible confusion that might portend on the part of my site mates.

At the core, my thinking was this. 'Selling the sizzle, not the steak" - the benefits, not the features - is a basic selling principle that's been around for thousands of years. We all know that people buy a 1/4-inch drill so that they can make a 1/4-inch hole. But I'm always amazed at how many businesses, large and small, keep on plugging the features of their product or service, rather than the benefits.


As a journeyman engineer, it has become clearer to me that in order to build a system you must first sell it. Spending a lifetime in dealing with facts and their stark consequence in harsh reality I am quite inept in the spin game. In the world of politics and opinion, the place where our future fate rests, reality is an illusion skillfully crafted by the right words and phases endlessly repeated until they are accepted unquestionably as self evident. I therefore decided with the help of my site mates to practice in this sheltered environment to get the sizzle down correctly. I obviously have a long way to go.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 27, 2008 9:50 am 
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Combining a fusion source with a fission reactor is an interesting concept, though I've never have seen someone use the sentence

"simple, inexpensive, compact, and rugged machine. Because of the quality of it materials and simplicity of design, it is easy to maintain. It is factory buildable with all the advantages that mode of production affords,"

If you want to know more of the ideas behind this concept I would suggest to take a look at P. Rebut his papers.

And this type of reactor is quite proliferation sensitive...to say the least...

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 27, 2008 10:32 am 
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STG wrote:
Combining a fusion source with a fission reactor is an interesting concept, though I've never have seen someone use the sentence

"simple, inexpensive, compact, and rugged machine. Because of the quality of it materials and simplicity of design, it is easy to maintain. It is factory buildable with all the advantages that mode of production affords,"

If you want to know more of the ideas behind this concept I would suggest to take a look at P. Rebut his papers.

And this type of reactor is quite proliferation sensitive...to say the least...


Quote:
though I've never have seen someone use the sentence


I paraphrased an old jeep commercial that rings through my mine on occasion. It may be a bit strong for a reactor though.

Quote:
And this type of reactor is quite proliferation sensitive...to say the least...


Not really. It’s just another type of Lftr. What does it matter where the neutrons come from; enriched fuel or fusion.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 27, 2008 10:38 am 
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One can also get neutrons from spallation sources; this was the idea behind accelerator transmutation of wastes. Of course, it could also drive a sub-critical pile.

Interesting Letter to the Editor in todays Wall Street Journal from Neil Armstrong. In part:

"Engineers are painfully honest and insist on presenting any assumptions used in their decision process. Therefore a conclusion can only be challenged when an erroneous assumption can be identified. Because this approach is somewhat unfamiliar in business and politics, its importance is ofter overlooked"

I thought the last sentence was more than kind.


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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 27, 2008 2:10 pm 
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Axil wrote:
Not really. It’s just another type of Lftr. What does it matter where the neutrons come from; enriched fuel or fusion.


It matters! just like the source intensity matters and so on....

I won't go into the theoretical details and so on, but the combination of a molten salt and a fusion source creates quite a number of proliferation sensitive issues.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 27, 2008 8:47 pm 
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STG wrote:
Axil wrote:
Not really. It’s just another type of Lftr. What does it matter where the neutrons come from; enriched fuel or fusion.


It matters! just like the source intensity matters and so on....

I won't go into the theoretical details and so on, but the combination of a molten salt and a fusion source creates quite a number of proliferation sensitive issues.


I’m interested. Can you list the most prominent and sensitive ones that exceed those already present in the Lftr. By the way, I remember from your previous posts that you consider the Lftr to be more proliferation sensitive than other reactor types.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 28, 2008 8:25 pm 
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Tungsten is an ideal material to form the containment sphere of the LFTR fusor. It is very dense which makes it unparalleled in the conduction, transmission, and concentration of acoustic waves that TMF requires. It is twice as dense as the steel that General Fusion is planning to use in their approach with the resulting doubling of acoustic force at the point of fusion.


The high transparency of tungsten to high energy neutrons is another advantage. In such a core containment vessel few neutrons are wasted by the core barrier material letting them pass into the thorium blanket for transmutation into the fissile component of other Lftr type reactors.


A very large blanket layer of thorium fluoride surrounding the core vessel also has great advantage. It increases the thermal inertia that maximizes the safety of the Lftr and also provides additional surface area to mount many more acoustic generator units that can be downsized on an individual basis due to their greater numbers and can be spread more evenly spaced over a greater surface area.


Image


The one disadvantage is the increased cost of fabrication of a thick tungsten containment sphere for the blanket it being at least 6 meters or more in diameter. Such a mammoth sphere is very heavy and difficult to form in large sections whose engineering is a challenge in their fabrication.


In fusion, big is beautiful, and on the scale that is common in fusion today where a man’s size is dwarfed by a towering cathedral of pipes and superconducting magnets such large size is understandable, acceptable, and even very beautiful.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 29, 2008 1:45 am 
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Resource:

http://www.talk-polywell.org/bb/viewtop ... 7&start=15

<snip>

The mechanical problems(with the general fusion approach) are daunting. Getting 200 steam pistons operating together to within 100 nS of each other (mechanical tolerances not given nor length of motion) to provide 1 uS of confinement is no easy task.

Mechanical resonances alone may make it impossible. Friction and wear variables complicate things.

One of the things to consider is the speed of sound in steam (it determines the rate at which forces can be applied). At room temp and pressure you are looking at ~340 m/S for air. The upper range for a detonation wave in high explosives is 10,000 m/S. Speed of sound in Steel is 6,000 m/S. Diamond 12,000 m/S. Speed of sound in water is ~1,400 m/S. In mercury about the same. I would expect a lead/lithium mixture around that range i.e 500 m/S to 3,000 m/S. So that gives some idea of the speed of a pressure wave through the material.

And then you have to maintain an steam inlet pressure constant with all the valves pulsing. Then conduct all the exhaust properly away from the machine to prevent differential heating.

I believe electromagnetic field approaches(The Lftr fusor appoach) show more promise. At least from an engineering standpoint.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 29, 2008 4:05 pm 
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In an Lftr fusor, the barrier wall that separates the core and blanket salts is also a reflection wave barrier to the acoustic waves that must travel through the blanket wall and into the core salt to the point of fusion. This barrier can be overcome by placing tungsten directly connected solid rods between each of the 200 acoustic generator contact points on the blanket wall and the core barrier wall. These rods will conduct acoustic wave energy at 100% efficiency directly to the core wall at the speed of sound in tungsten.


It might also be possible to reflect wave energy from the fusion explosion at the center of the core by the core wall back to the fusion detonation point. The control computer can time the next acoustic wave from the blanket wall to reinforce the fusion rebound wave with exact blanket wall wave generation timing. This can use waste fusion wave energy to reinforce and supplement the next acoustic wave.

See the figure below for a diagram.


Attachments:
rods.jpg
rods.jpg [ 47.45 KiB | Viewed 2482 times ]

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 29, 2008 10:28 pm 
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Reference:

http://www.generalfusion.com/files/acoustic_wave.pdf

The referenced document contains simulations and descriptions of the wave forming fusion process. The fusion acoustic wave must be precisely formed and have the proper amount of energy to be successful. The wave production research process is one that will be involved and time consuming; not an easy job. General fusion wants to use steam power to generate the wave. I don’t know about that. Computer control and timing is more precise, adaptable, and repeatable which I think has a better chance of success.

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 Post subject: Re: Lftr/MTF hybrid
PostPosted: Dec 30, 2008 7:18 am 
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Does it really have to be so hard?
I imagine you could slowly build up resonating standing waves with very high compression without having the supply the whole energy in one pulse.
If you look at sonoluminescence for example. Vibrate a water jar and you get a glowing bubble in the center (ok it's not very easy, but average university physics labs do it). (Rusi Taleyarkhan claimed neutron production from heavy water sonoluminescence experiments a couple of years ago but it has not been reproduced AFAIK.)


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