Inertial Confinement Fusion

tahanson43206 · 2022-03-18 06:13:39

This topic is offered for those members who would like to focus on Inertial Confinement Fusion as a specific discipline.

The topic was suggested by Calliban, in one of the profusion of general fusion topics present in this forum.

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tahanson43206 · 2022-03-18 07:40:49

For Calliban .... your mention of the possibility that an ion beam might be more efficient/effective in igniting an inertial confinement package, as compared to laser beam ignition which is under active study, leads to the observation that accelerators of various kinds have been developed over many decades for scientific research, and for production of medical isotopes.

The kind of accelerator that seems (to me at least) most applicable to the Inertial Confinement ignition process is the well known linear accelerator.

I asked Google for any information it might have on linear accelerators in Great Britain, and it came back with a citation from the medical field ...

I had not realized the extent of the use of linear accelerators for treatment of medical conditions.

the article Google found is from: pubmed.ncbi.nlm.nih.gov. The article reports 135 Linacs installed in UK ... (as of 1990)

These appear to all be electron accelerators.... your post mentioned ions, so scientific accelerators may be better suited for your investigation.

I'll revise the search ...

This time Google found an article from May of last year ... UK to play vital role in creating the world's most powerful ...
May 12, 2021 - In the UK, STFC will design, build and qualify vital elements of the 215 meter long particle accelerator...

Opening the article, I find that the instrument is intended to study neutrinos.

A disappointment (from the perspective of UK as a site) is that the instrument is to be build at Fermilab in the US.

However, there may be other instruments in the UK that could deliver the ignition punch you need to prove your theories.

Obviously it would be a feather in UK's cap to achieve break even with your design, even if it doesn't achieve economic break even.

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tahanson43206 · 2022-03-18 07:56:50

In an earlier post to Calliban, I pointed out the opportunity to adapt a hybrid fission/fusion space propulsion system for use generating power on Earth.

Depending upon the size of the package Calliban may design, it might be possible to mount one of these engines at the tips of a rotating beam in a large vacuum chamber, so that the beam rotates to drive a shaft which itself drives a generator.

While such an facility would large, it could (presumably) serve a large metropolitan area with significant flows of electrical power without producing a single molecule of CO2.

I bring this up in the context of the Inertial Confinement topic, because a linear accelerator may be able to furnish the ignition conditions needed for Calliban's design, and a linear accelerator could (of course) reside on the rotating arm ahead of the ignition location.

The putt-putt nature of the device leads to the suggestion to alternate putts at the two ends of the beam, so that power is delivered at twice the frequency that would otherwise occur. The beams could be designed to flex so as to even out the flow of force to the drive shaft, and the mass of the generator will act as a flywheel. Such a machine would be a sight to see, through safety glass, or perhaps through remote TV monitors if radiation is a concern.

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Calliban · 2022-03-25 17:24:11

Nuclear Fusion describes the process by which light isotopes, principally those of hydrogen, fuse together to give rise to heavier isotopes. This results in the release of substantial binding energy, usually in the form of kinetic energy of the products. For Fusion to occur, two light nuclei must approach one another with sufficient kinetic energy to overcome the coulomb barrier resulting from their mutual positive electric charges. If kinetic energy is insufficient, Fusion may still occur via quantum tunnelling. However, at low temperatures, this occurs at such a low rate as to be undetectable. To generate useful quantities of power, the fuel must be raised to a sufficiently high temperature (5-15KeV) and must be confined at a sufficient density for a long enough confinement time.

For a plasma to ignite, the energy added to it by Fusion reactions must equal the energy losses at the that temperature. Following ignition, it is no longer necessary to externally heat the plasma. Neutrons will stream out of the plasma, depositing very little energy. Only charged particles add energy to the plasma itself. Breakeven occurs when the reactions within the plasma generate more energy than is required to create Fusion conditions. This does not necessarily imply that the Fusion reactions will be used to generate electrical power.

The reaction rate within a plasma is a function of particle density and temperature (average collision energy). Total energy generated within the plasma is also a function of confinement time. The Lawson Criterion describes the product of these three properties sufficient to generate energy equal to that required to produce the Fusion plasma. For a practical energy producing reactor, the energy yield must be many times greater than breakeven, to allow for energy conversion losses and for reasonable power output from the capital investment in the device.

Two methods of producing a practical reactor are being pursued here on Earth. The first involves confinement of a relatively diffuse hydrogen plasma at temperatures of 10KeV in magnetic fields. Typical pressure is 5-10bar and confinement time must exceed several seconds. The problems with this approach are limitations on achievable magnetic confinement pressure, which limits the power density of the device.

The second method is inertial confinement. This involves using lasers or some other driver to compress a mass of solid Fusion fuel to extremely high density and to heat some or all of the fuel to ~10KeV, at which point a detonation wave propagates through the fuel. The confinement time is extremely short and is essentially the ratio between the speed of sound in the compressed pellet and its radius. Typical confinement times are around 1E-11 seconds. The extreme density of the pellet during compression, allows Fusion to complete in this very short confinement time.

Pellets are structured with multiple layers. An outer plastic layer serves as an ablasion surface. Beneath this, is a layer of solid DT, which is turn surrounds a hollow, filled with DT gas. Laser light converts the outer plastic surface into plasma, which exerts megabar forces onto the surface of the pellet, imploding it at velocities of around 200km/s. A typical pellet contains around 1mg of fuel and weighs 2mg in total, with a diameter of 1mm. In the 1970s, when IC Fusion was first investigated, it was assumed that the entirety of fuel in a 1mg pellet must be both compressed to high density and heated to Fusion temperatures. This is termed 'Volume Ignition'. However, this was found that volume Ignition would require around 60MJ of driver energy to ignite 1mg of fuel, which made commercial energy production unlikely and laser costs extremely high. A number of things came to be realised from work carried out in the 1970s.

1. It takes a lot more energy to heat a mass of material than it does to compress the material to very high density (about 1GJ of energy per gram) vs 10MJ per gram for compression.

2. Compressing hot material greatly increases the amount of energy needed to achieve compression.

3. Lasers are very inefficient means of transferring the energy needed to generate Fusion. This is due to the combination of poor efficiency of the laser in generation of light and poor absorption of laser light due to the opacity of dense plasma generated at the pellet surface. For each joule of energy absorbed by the pellet, around 100J of input energy was needed for the laser.

4. Unless very large numbers of lasers are used, which is expensive and complex, instabilities can develop during compression. This is due to uneven distribution of laser light on the pellet surface. To mitigate this problem, indirect drive approaches were developed. The pellet was housed within a high-Z container called a hohlrem. Laser light would impact the container, generating x-rays, which would evenly heat the pellet surface allowing instabilities to be avoided. The efficiency of conversion of laser light to x-rays is around 75%.

The difficulties involved in achieving Volume Ignition, let to development of the hot spot approach. It was realised that in an imploding fuel pellet, only a small proportion of the fuel, about 2% at the centre of the pellet, needed to reach Fusion conditions. When Fusion begins within the core, temperatures rise sufficiently to develop a detonation wave, which rapidly passes through the entire pellet, consuming it within the confinement time. It is estimated than only 1-2MJ of energy are required to compress the pellet to >800g/cm3 and heat the central hotspot to 10KeV.

However, whilst experiments have succeeded in generating extremely high densities (which is energy cheap) temperatures at the centre of fuel pellets have reached only a few hundred KeV. This is more than 1 order of magnitude short of the temperatures needed to achieve hot spot Ignition. The fast ignition approach was intended to solve this problem, by injecting precisely targeted quantities of heat at the centre of a fuel pellet following compression. However, this is a cumbersome process that requires precise timing and aiming of lasers. First, a laser must be used to drill into the compressed pellet. A second laser then injects heat into the centre of the pellet, through the hole drilled by the first laser. Timing must be accurate to 1E-12 seconds and the laser must hit the compressed target within a few nanometers of dead centre.

Last edited by Calliban (2022-03-25 17:33:02)

Calliban · 2022-03-25 18:05:59

Following from perious Post.

Two important innovations are possible, that make IC Fusion a far more practical and near term prospect for energy production. Firstly, the extremely poor energy efficiency of compression can be avoided, if lasers are replaced with ion beams. Charged particle accelerators can deliver energy to a fuel pellet surface with 30% efficiency, versus <1% for lasers. This dramatically improves the energetic efficiency of IC Fusion.

Secondly, the extreme density achievable in an imploding fuel pellet, up to 1000x the density of water, is high enough to allow tiny quantities of fissile materials to provide the energy needed to generate hot spot conditions. Critical mass is inversely proportional to the square of density. This implies that compression of fissile material by a factor of 1000, would reduce critical mass by a factor of 1million, down to a few mg. The reflection provided by the compressed Fusion fuel reduces critical mass to even smaller levels. Furthermore, as compression proceeds, fission events in the subcritical core will send fission products with 160MeV of energy into the compressed Fusion fuel. At the densities occurring in the core, these would deposit all of their energy within 1nm of the fissile surface, heating ions far above Fusion ignition temperature. Fusion events would generate fast neutrons. Around half of these would enter the fissile core, where they would generate more fission, sending more fission products into the surrounding Fusion fuel, and so on. This nanoscale coupling between fission and Fusion stage, is sufficient to reduce critical mass still further, down to nanograms. The extremely short range of fission products in highly compressed matter (~1E-9m), would ignite Fusion fuel in the highly localised region within a few nanometers of the fissile core. Fusion products and electrons would then heat surrounding fuel, generating a detonation wave.

The use of fissile materials to generate the heat required for hot spit ignition, removes the requirement for the driver to provide any energy for pellet heating. The function of the driver can be simplified to provide entirely compressive energy. This and the much higher efficiency of ion beam drivers, allows the potential for electrostatic accelerators to be used for ion acceleration. The use of these accelerators limits ion energy to a few MeV. However, efficiency can reach 90% and these accelerators are compact enough to allow their use in realistic space drives.

The only remaining unanswered question is how much fissile material is needed to heat the hot spot? If we go with previous estimates for thermal energy requirements of about 1MJ, then about 4E16 atoms of 235U will be needed to ignite a 1mg fuel pellet. That is about 16 nanograms, or about 1% of total fuel mass and about 0.1% of total energy yield. For larger fuel pellets, the amount of Uranium needed would scale down as the hot spot energy requirements would remain constant with increasing yield. So pellet Fusion would get even cleaner as it scaled up. For yields 100x greater, pellet diameter would be around 4mm and fission would yield only 1E-6 of total propulsive energy. That should be clean enough to use in Earth atmosphere.

Last edited by Calliban (2022-03-25 18:13:27)

Terraformer · 2022-03-26 03:58:03

So, externally ignited microthermonuclear bombs?

tahanson43206 · 2022-03-26 06:38:39

For Terraformer re #6

Thanks for picking up on Calliban's initiative!

While Calliban is concentrating on space propulsion, I am hoping his ideas lead to a more efficient, and safer way to harness atomic power than the cumbersome methods employed since Fermi and his team "ignited" the first fission reaction under the old stadium steps at the University of Chicago, in 1942.

It is 80 years on, and every single non-military implementation of fission technology uses the same technique.

Calliban's vision is spread over three topics... you can find some of his work in the "Nuclear is Safe" topic, and some in the "Hybrid Fission Fusion" topic.

It fits well into this topic, because it would employ Inertial Confinement, but he has changed the technology from lasers to an ion beam.

I like the ion beam idea, because it is so ** very ** well established as a technology. A recent post somewhere in the forum reported on the (to me surprising) number of linear accelerators operating in the UK for medical purposes.

While those devices (apparently) produce electron beams, the technology itself can be used to accelerate protons and even larger ions, so I'm hoping they will show up in Calliban's musings at some point.

What I'm ** really ** rooting for is a method of using atomic energy (as visualized by Calliban and described by Terraformer) to deliver significant heat energy to the "ancient" technology of steam and gas engines of the 1890's through about 1930.

Since the output of Calliban's vision is thermal energy, driving a piston allows for direct conversion of that energy into useful motion, while the thermal energy not captured by the piston can be drawn off as heat in the cooling fluid, and thus contribute to the overall performance of the machine, whether that heat is enlisted directly to make energy, or simply used to heat a building.

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tahanson43206 · 2022-11-14 13:28:03

Here is an update on Inertial Confinement research...

If I understand the report correctly, more energy is produced than models had predicted.

https://www.msn.com/en-us/news/technolo … c20a7bfedb

Nuclear Fusion Experiment Just Made Something Very Strange Happen
Jess Thomson - 3h ago
In a recent study, charged atoms, also known as ions, have been found to behave strangely during nuclear fusion reactions, in ways that scientists did not expect.
Stock image of an atom. Nuclear fusion experiments have found that ions in nuclear fusion reactions behave differently to what was expected.
Stock image of an atom. Nuclear fusion experiments have found that ions in nuclear fusion reactions behave differently to what was expected.
© iStock / Getty Images Plus
According to a paper published on November 14 in the journal Nature Physics, researchers at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory discovered that when deuterium and tritium ions, which are isotopes of hydrogen with one and two neutrons, respectively—are heated using lasers during laser-fusion experiments, there are more ions with higher energies than expected when a thermonuclear burn starts.

"The process of inertial confinement fusion (ICF) squeezes a small (1mm radius) capsule filled with a layer of frozen deuterium and tritium (isotopes of hydrogen) surrounding a volume of deuterium and tritium gas down to a radius of about 30 micrometers. In the process, these isotopes of hydrogen ionize and a plasma of electrons, deuterium and tritium nuclei [is the result]," Edward Hartouni, a physicist at NIF and a co-author of the paper, told Newsweek.
"This plasma is so dense that collisions of these charged particles (electrons and ions) happen very frequently," Hartouni said. "At low temperatures, the ions mostly scatter elastically, as if they were billiard balls. But as the temperature of the plasma increases, which it does as it is squeezed, some of these collisions result in the fusion of the ions. The fusion releases tremendous energy."
"Of the three types of fusion that can occur, the fusion of the deuterium and tritium ions occurs more frequently, and releases the largest amount of energy," he continued. "This energy is in the form of the kinetic energy the fusion [produces], which for deuterium and tritium fusion are an alpha particle (the helium ion) and a neutron," Hartouni said.
In essence, the lasers heat the hydrogen fuel to enormous energy levels, leading them to collide and fuse together to form helium atoms—this is the reaction that powers the sun. This reaction also releases huge amounts of energy, which further heats the hydrogen fuel.
This extra energy can eventually power the reaction without the need for the lasers, having become what is known as a "burning plasma." This "ignition" was only achieved for the first time in 2021, also by NIF, in a milestone achievement for the field.
"If the conditions are right, this process 'runs away' and we have thermonuclear burn," Hartouni said. "It is the goal of the research to study the conditions that lead to controlled thermonuclear burn, which could be an energy-producing technology."
"The goal of the National Ignition Facility is to study this process and learn how to create these conditions. NIF is the first facility to routinely achieve burn plasma conditions and enable experiments to compare with our theoretical expectations. We would expect to be surprised as we haven't (previous to NIF) been able to study burning plasmas experimentally," Hartouni said.
The researchers measured the temperature of deuterium and tritium fuel ions by analyzing the distribution of the neutrons that are flung out during these fusion reactions and found that there are more ions with higher energy in reactions where a burning plasma is achieved compared to previous experiments with non-burning plasmas. This suggests, the authors say, that ions behave differently in a burning plasma.
"We don't know the reason for this at the moment. We have looked back at previous shots and see that our most 'successful' shots have a larger departure from our expectation than the 'unsuccessful' shots; the measure of success being how large the shot yield (measured in the number of neutrons produced) compared to the calculated yield. Since the latest data point in the paper, subsequent shots with higher yields, and thus more robust thermonuclear burn, reveal that this departure from Maxwellian behavior is getting larger," Hartouni said.
These results are surprising, and show the importance of funding for research in such a growing field, said Stefano Atzeni, a physicist at the Università di Roma "La Sapienza", in Italy and author of an accompanying Nature Physics News and Views paper.
"This result has only been possible thanks to extremely sophisticated (and large, and expensive!) instrumentation. The main lesson learned from these measurements is that when a new 'regime' is entered, fundamental research is needed. Theoretical expectations help, but must be confirmed," he told Newsweek.
"These results make clear that we cannot take for granted our models, developed for plasmas under different conditions. More generally, the lesson is that we cannot rely on large extrapolations of previous results."
The results will also help to make future experiments in fusion more accurate.
"The design of possible future laser-fusion energy sources will depend on our ability to make simulations, and those simulations rest on the foundation of our basics science understanding of the process," Hartouni said. "The simulations are based on models, and experimental results allow us to confront these models with reality. This study explores the new territory opened up by NIF creating burning plasmas, and the sophisticated set of diagnostics, both the hardware and the analysis which have been developed for this exploration."
"As we extend our observations and analysis of the experiments, and conduct new experiments to address our hypotheses, we will inform our basic science understanding of the laser-fusion process," Hartouni said. "This understanding will allow us to incorporate more realistic models and make better predictions of the laser-fusion process on which to base potential future designs."
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about nuclear fusion? Let us know via science@newsweek.com.
Related Articles

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Calliban · 2022-11-14 23:05:03

tahanson43206 wrote:

The researchers measured the temperature of deuterium and tritium fuel ions by analyzing the distribution of the neutrons that are flung out during these fusion reactions and found that there are more ions with higher energy in reactions where a burning plasma is achieved compared to previous experiments with non-burning plasmas. This suggests, the authors say, that ions behave differently in a burning plasma.
"We don't know the reason for this at the moment. We have looked back at previous shots and see that our most 'successful' shots have a larger departure from our expectation than the 'unsuccessful' shots; the measure of success being how large the shot yield (measured in the number of neutrons produced) compared to the calculated yield. Since the latest data point in the paper, subsequent shots with higher yields, and thus more robust thermonuclear burn, reveal that this departure from Maxwellian behavior is getting larger," Hartouni said.
These results are surprising, and show the importance of funding for research in such a growing field, said Stefano Atzeni, a physicist at the Università di Roma "La Sapienza", in Italy and author of an accompanying Nature Physics News and Views paper.

Interesting. This demonstrates the problem with extrapolation from theoretical models.

In IC fusion, ignition starts in the centre of the pellet and spreads outward as a detonation wave. The burn progresses so rapidly that there is insufficient time for the ions in the pellet to thermalise. If you model the explosion as a series of time steps, the plasma at the centre will be much hotter than the exterior during the initial stages. The enormous density of the outer layers, which still have considerable opposing momentum at the time of ignition, will cause them to deflect ions and radiation back into the core, resulting in very high temperatures. At the density prevelant in an ICF pellet, heat transfer is dominated by conduction. This takes time, because the superheated fusion products have a range of nanometres in the colder, denser and highly compressed outer shell hydrogen. It takes time for collisions to distribute energy in a solid with such high density.

Last edited by Calliban (2022-11-14 23:10:04)

Calliban · 2022-12-15 12:36:10

Inertial confinement fusion energy breakthrough.
https://nypost.com/2022/12/13/scientist … ried-away/

The latest experiment produced 3MJ of fusion energy for 2MJ of laser energy input to the target. That achieves technical breakeven. Unfortunately, some 200 units of electric energy are consumed by the lasers to produce each unit of laser energy absorbed by the target. Energy released by fusion, will be a mixture of x-ray, UV, visible and neutron radiation. This must be absorbed by the reactor walls and captured as heat in a working fluid. Conversion of heat into electric power in a steam plant will be 33% efficient. For the powerplant to break even, the ratio of output / input must improve 400x over what has been achieved already. A long way to go.

tahanson43206 · 2023-08-07 12:18:14

Here is an update on the National Ignition Facility, from an unlikely source...

For some reason the Yahoo feed seems to think i'd be interested in an article about fusion from a town in Michigan.

It turns out a leading figure in the management of the work force to coordinate 128 ultra high powered lasers is a native of Traverse City, Michigan.

https://www.yahoo.com/news/faith-fusion … 00620.html

The Record-Eagle, Traverse City, Mich.
Faith and fusion: Annie Kritcher makes clean energy breakthrough
1
Michael Breazeale, The Record-Eagle, Traverse City, Mich.
Sun, August 6, 2023 at 2:35 PM EDT
Aug. 6—TRAVERSE CITY — Andrea "Annie" Kritcher designed an experiment that enables scientists to produce energy from nuclear fusion, which could result in a clean, limitless source of energy for the planet.
<snip>
Apache Internal Server Error blocked the rest of this post
<snip>
"Her research could really change the trajectory of our planet," Coughlin said. "I'm just so proud of her. And I'm so happy she's here. I feel lucky to be on the planet at the same time as Annie. Her work shows great promise for humanity."

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#1 2022-03-18 06:13:39

Inertial Confinement Fusion

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Re: Inertial Confinement Fusion

#3 2022-03-18 07:56:50

Re: Inertial Confinement Fusion

#4 2022-03-25 17:24:11

Re: Inertial Confinement Fusion

#5 2022-03-25 18:05:59

Re: Inertial Confinement Fusion

#6 2022-03-26 03:58:03

Re: Inertial Confinement Fusion

#7 2022-03-26 06:38:39

Re: Inertial Confinement Fusion

#8 2022-11-14 13:28:03

Re: Inertial Confinement Fusion

#9 2022-11-14 23:05:03

Re: Inertial Confinement Fusion

#10 2022-12-15 12:36:10

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