Big announcement about fusion energy coming soon (Dec-2022)

[PAllen]

I thought I might find sourcing for the idea that everyone always said commercial fusion was 20 to 40 years away. Certainly that is my impression, having followed the field at varying levels of expertise since the early 1960s. However, instead, I found a booklet from the USAEC on controlled fusion by the eminent Samuel Glasstone (from 1964) that concludes “how long it takes to achieve is impossible to predict. There are problems of enormous difficulty to be solved …”

I found two more publications from this period in my personal collection, and both echo the same theme: no fundamental reason commercialization shouldn’t be possible, but the problems are too formidable to warrant any prediction. I really wonder now about the process of manufactured memory - I have such clear apparent memory of this ever moving target, but can find no sign of it in my contemporaneous sources.

 

[Nathi ORea]

Hello.
I am sure like everyone, I am really intrigued by this news of a positive net energy out of a fusion reaction.
I don't have a background in physics or anything, but I was wondering some stuff.
The net energy they got out of this... my understanding it is the actual amount of heat out of the reaction... maybe the kinetic energy of any particles created out of it as well? They actually didn't create electricity from it did they?
If this is right.. still seems a long way off if this apparatus was not even set up to produce electricity... So you have to get all the engineering around that... as well as any inefficiencies with converting thermal energy to electricity.
I am not that well versed in it.. but when i hear it explained, it seems a lot like an implosion nuclear bomb device. It almost seems to be this apparatus seems more like another way to create a hydrogen bomb rather than actually create electricity.
I am trying to get excited about this, but this threshold almost seems like an arbitrary goal to me.

 

[bob012345]

I thought I might find sourcing for the idea that everyone always said commercial fusion was 20 to 40 years away. Certainly that is my impression, having followed the field at varying levels of expertise since the early 1960s. However, instead, I found a booklet from the USAEC on controlled fusion by the eminent Samuel Glasstone (from 1964) that concludes “how long it takes to achieve is impossible to predict. There are problems of enormous difficulty to be solved …”

I didn't take it as an actual prediction of when fusion will arrive as much as all during the past half century or so if you asked when will practical fusion be available it would seem as there is at least twenty more years of progress required. It's always been true and remains so even today.

 

[Drakkith]

They actually didn't create electricity from it did they?

No. They didn't even create more energy than they ended up using. What they did was create more energy out of the fuel pellet than they pumped into the pellet using lasers. Due to inefficiencies in the lasers and other machinery, the actual full amount of energy used was a hundred times more than they got out of the fusion.

But it is progress. So that's something.

I am not that well versed in it.. but when i hear it explained, it seems a lot like an implosion nuclear bomb device.

Yes, this is basically what inertial fusion is. Mini fusion bombs going off inside a controlled environment.

It almost seems to be this apparatus seems more like another way to create a hydrogen bomb rather than actually create electricity.

Every time a car engine fires one of its cylinders it is like a small conventional bomb going off. Would you say that a car engine is just another way to create bombs?

I am trying to get excited about this, but this threshold almost seems like an arbitrary goal to me.

Add the end of the day everything is arbitrary to some extent. But getting more energy out of a reaction than you put into it, even if you're ignoring inefficiencies, sounds like a pretty natural spot to put a threshold to me.

 

[hutchphd]

Yep.
P.T. Barnum would be proud.

 

[Nathi ORea]

No. They didn't even create more energy than they ended up using. What they did was create more energy out of the fuel pellet than they pumped into the pellet using lasers. Due to inefficiencies in the lasers and other machinery, the actual full amount of energy used was a hundred times more than they got out of the fusion.

But it is progress. So that's something.Yes, this is basically what inertial fusion is. Mini fusion bombs going off inside a controlled environment.Every time a car engine fires one of its cylinders it is like a small conventional bomb going off. Would you say that a car engine is just another way to create bombs?Add the end of the day everything is arbitrary to some extent. But getting more energy out of a reaction than you put into it, even if you're ignoring inefficiencies, sounds like a pretty natural spot to put a threshold to me.

No. They didn't even create more energy than they ended up using. What they did was create more energy out of the fuel pellet than they pumped into the pellet using lasers. Due to inefficiencies in the lasers and other machinery, the actual full amount of energy used was a hundred times more than they got out of the fusion.

100 times! Wow! Where does all the rest of the energy go?

Every time a car engine fires one of its cylinders it is like a small conventional bomb going off. Would you say that a car engine is just another way to create bombs?

I guess i was thinking that it would be similar to how a plutonium implosion bomb could not be used for electricity production. It is just impractical. Perhaps they could run it like a internal combustion engine.. Have the fuel run continuously into a cylinder and turn a crank? because it is a gas and not a metal like plutonium?

Thanks so much for replying. I really appreciate it.

 

[Nathi ORea]

Yep.
P.T. Barnum would be proud.

I can't help but think the media are giving the wrong impression about what this news actually means. When you do a little more digging, it honestly doesn't seem that big a news to me. I mean.. they are constantly getting better at it.. I don't think it really means we are any closer to 'it' than we were yesterday.

Edit: I guess i mean we aren't any closer to 'it' with this advancement than we have been with any other improvement of efficiency.

 

[256bits]

I can't help but think the media are giving the wrong impression about what this news actually means. When you do a little more digging, it honestly doesn't seem that big a news to me. I mean.. they are constantly getting better at it.. I don't think it really means we are any closer to 'it' than we were yesterday.

Edit: I guess i mean we aren't any closer to 'it' with this advancement than we have been with any other improvement of efficiency.

I am not that well versed in it.. but when i hear it explained, it seems a lot like an implosion nuclear bomb device. It almost seems to be this apparatus seems more like another way to create a hydrogen bomb rather than actually create electricity.

Frankly that is what it is - how small can one make a fusion bomb, or how big, so that it doesn't blow your apparatus apart.
Theirs is quite small.

One problem with this design involves the 'bomb' pellet containing the fusion material, the casing, the temperature rise and implosion to squeeze the fusion material to fusion temperature,... It is not just a put a pellet in there and hope for the best, though it probably was kind of that in the beginning in a matter of speaking. A lot of thinking and tech went into that small pellet. This is the threshold part where they did get more energy out from the fusion than what went into the pellet, so they must be doing something right.

Another problem is the system used to heat the pellet. A gigantic energy hungry system - they may have to work on that some more to reduce the energy taken from the grid. Right now, they have to wait for that system to cool down before shooting in at another pellet.
The third problem, for all fusion systems, no matter of what type, is how to harness the energy from fusion to make it useful. Yes, that would be akin to a regular steam plant.

There is a long way to go before actual fusion for the masses becomes available. As someone said, this knocked the

Perhaps they could run it like a internal combustion engine.. Have the fuel run continuously into a cylinder and turn a crank

That is what is hoped to be achieved in the end - a continuously running fusion reactor.
The comment is just too general and old hat to be of any use for a fusion design team - they all know that is the goal.

 

[Drakkith]

100 times! Wow! Where does all the rest of the energy go?

Various inefficiencies. There are losses literally everywhere in the energy-to-laser-to-target chain.

I guess i was thinking that it would be similar to how a plutonium implosion bomb could not be used for electricity production. It is just impractical.

Fortunately for nuclear power, heavy elements like uranium or plutonium already want to fly apart, so there's no need to compress them. All you need to really do is bring them close to each other in a large enough amount and you'll get a nice, steady, controllable chain reaction.

But, if we wanted to, we could almost certainly compress uranium like we do fusion fuel pellets for power generation. It would be nearly identical to a standard nuclear warhead, where the plutonium or uranium is compressed by conventional explosives to set off the nuclear chain reaction that leads to detonation. We don't do this because we don't need to, as it's really, really easy to get a controllable chain reaction from fission just by shoving a couple of blocks or rods of material close together.

: I guess i mean we aren't any closer to 'it' with this advancement than we have been with any other improvement of efficiency.

The path to every major development is tiled with small footsteps.

 

[hutchphd]

We don't do this because we don't need to, as it's really, really easy to get a controllable chain reaction from fission just by shoving a couple of blocks or rods of material close together.

The same is true for fusion, but unfortunately the blocks need to be the size of the sun. That is an inconvenient truth.

 

[PeterDonis]

heavy elements like uranium or plutonium already want to fly apart, so there's no need to compress them

I think you mean "want to stay together", not "want to fly apart".

 

[Drakkith]

I think you mean "want to stay together", not "want to fly apart".

I meant that as a very rough way of describing their radioactivity. Just wait a bit or tap them with a neutron and they come right apart!

 

[gmax137]

Just a few caveats. I hope this doesn't come across as argumentative.

Every time a car engine fires one of its cylinders it is like a small conventional bomb going off.

Well, not really. The gasoline-air mixture in a cylinder burns, it does not explode. There may be a fine line between "rapid combustion" and "explosion", but the ICE engine is on the combustion side of the line. There is a flame front, not a shock wave.

really, really easy to get a controllable chain reaction from fission just by shoving a couple of blocks or rods of material close together

It's easier than making a fusion machine, but "really, really easy" undersells the actual difficulties. Especially the "controllable" part. It's not quite that easy.

 

[Astronuc]

Some background on NIF - https://lasers.llnl.gov/content/assets/docs/for-users/nif-user-guide.pdf
See page 29ff.

"The NIF 192-beam neodymium glass laser is capable of delivering up to 1.8 MJ of total energy and up to 500 TW of peak power at the third harmonic (351 nm, commonly referred to as “3ω”) of the fundamental 1.053 nm Nd:YLF frequency (“1ω”). Since its completion in 2009, the delivered energy and peak power have steadily increased to the peak values . . . "

In order to obtain 2.05 MJ, the power into the laser system would have to be about 570 MJ, assuming a linear scale. Perhaps the input can be reduced if the system is more efficient.

In the recent experiment, the 2.05 MJ input to the hohlraum resulted in an output of 3.15 MJ, or a get gain of 1.1 MJ as compare to the 500-570 MJ input for the laser system.

In the press release, important details are absent, even though there is a statement "Following the press conference, a technical panel of National Ignition Facility (NIF) scientists convened to discuss details of the achievement". There is no mention of the laser energy input, or the size/mass of the target.
https://www.llnl.gov/news/shot-ages...led-one-most-impressive-scientific-feats-21st

Most publications do not contain details other than "The successful experiment and fusion reaction input 2.05 MJ and released 3.15 MJ of energy, a higher threshold achieved than earlier indicated.*"
https://www.photonics.com/Articles/US_Department_of_Energy_Details_Net_Energy_Gain/a68586

APS get a little closer - https://physics.aps.org/articles/v15/195
"One of the main obstacles to commercialization is the overall efficiency of the process. Each firing of the lasers requires 300 MJ of electricity, meaning that the fusion reactions are operating at a net loss of 99% of the initial energy input."

But important details are lacking.

In the previous record shot, the experiment used ~477 MJ of electrical energy to get ~1.8 MJ of energy into the target to create ~1.3 MJ of fusion energy, according to a Wikipedia article, but I have not been able to verify the 477 MJ. Linearly extrapolating to 500 MJ from 477 MJ would imply 500/477*1.8 MJ = 1.88 MJ. Or alternatively based on 477 MJ to obtain 1.8 MJ on the target, one would need 543 MJ to obtain 2.05 MJ, which is better than 570 MJ, but still way more than 1.1 MJ net generation.An this is one shot, not multiple shots 1 sec apart. There is no heat transfer, no electrical production.

What did the holder look like after the ignition? How often would a holder be replaced? Presumbly the holder in a power reactor would also conduct useful heat to some system to generate electricity - or perhaps we use process heat. A lot of neutrons irradiating the holder. How would they produce more T fuel from the neutrons from the reaction?

How would one scale the experimental hohlraum by a factor of 1000: e.g., 1000 * 1.1 MJ = 1100 MJ, or by 3000 to obtain 3300 MJ of useful energy, meanwhile not scaling the laser system by 1000?

On the other hand, the shot generated 1.1 MJ, as opposed to a commercial PWR that generates 1100-1250 MJ/s of electricity from 3400-3800 MJ/s of thermal energy.

Another reference of earlier experiments
https://www.osti.gov/pages/servlets/purl/1184519

 

[PAllen]

Just a few caveats. I hope this doesn't come across as argumentative.Well, not really. The gasoline-air mixture in a cylinder burns, it does not explode. There may be a fine line between "rapid combustion" and "explosion", but the ICE engine is on the combustion side of the line. There is a flame front, not a shock wave.It's easier than making a fusion machine, but "really, really easy" undersells the actual difficulties. Especially the "controllable" part. It's not quite that easy.

And more caveats … deflagration vs. explosion with shock wave - gunpowder is definitely on the deflagrating side of this line, but few would disagree with calling rapid gunpowder deflagrations explosions.

 

[Drakkith]

It's easier than making a fusion machine, but "really, really easy" undersells the actual difficulties. Especially the "controllable" part. It's not quite that easy.

Sure it is. It's just not quite so easy to set things up in such a way as to safely generate lots of power and deal with the waste. Controlling the reaction can be as simple as making a brick of material and harnessing its heat as it sits there (RTG's in space probes as an example). The reaction rate is controlled by how large the brick is and how it is shaped.

 

[OCR]

The reaction rate is controlled by how large the brick is and how it is shaped.

.
And. . . whether or not you let the screwdriver slip. . . .
.

 

[pinball1970]

Various inefficiencies. There are losses literally everywhere in the energy-to-laser-to-target chain.

Fortunately for nuclear power, heavy elements like uranium or plutonium already want to fly apart, so there's no need to compress them. All you need to really do is bring them close to each other in a large enough amount and you'll get a nice, steady, controllable chain reaction.

But, if we wanted to, we could almost certainly compress uranium like we do fusion fuel pellets for power generation. It would be nearly identical to a standard nuclear warhead, where the plutonium or uranium is compressed by conventional explosives to set off the nuclear chain reaction that leads to detonation. We don't do this because we don't need to, as it's really, really easy to get a controllable chain reaction from fission just by shoving a couple of blocks or rods of material close together.

The path to every major development is tiled with small footsteps.

.
And. . . whether or not you let the screwdriver slip. . . .
.

Ouch. Introduced to the 'demon core' via pf. Horrific.

 

[Astronuc]

Controlling the reaction can be as simple as making a brick of material and harnessing its heat as it sits there (RTG's in space probes as an example). The reaction rate is controlled by how large the brick is and how it is shaped.

Actually the decay rate, or specific activity, is strictly dependent on the radionuclide and its half-life, which is unique to the nuclide. The energy and power are of course dependent on the quantity (mass) of material. An RTG is ON all the time; there is no turning it off.

 

[Drakkith]

Actually the decay rate, or specific activity, is strictly dependent on the radionuclide and its half-life, which is unique to the nuclide. The energy and power are of course dependent on the quantity (mass) of material. An RTG is ON all the time; there is no turning it off.

Of course. I only mean 'controllable' in the broadest sense. Nuclear power plants certainly have far more control over their reaction rates thanks to their design than a lump of fissile material does, not matter what its shape is.

 

[atyy]

https://www.theatlantic.com/technol...ear-fusion-breakthrough-nif-livermore/672439/
"Even if NIF is able to replicate the shot, perform similar ones consistently, and eventually increase the yield by five or tenfold, the experiment is still a dead end when it comes to meaningful energy production. Two megajoules is about the amount of energy released by burning a small chunk of kindling, so thousands upon thousands of such shots a day would be required before the energy production became in any way usable. Unfortunately, NIF’s lasers use huge slabs of glass that take hours to cool down between shots; in other words, they simply aren’t up to the task. (In fact, NIF was never meant to be a fusion-energy project but one designed for weapons research—another story altogether.)"

 

[Vanadium 50]

I don't think that follows. "Because the NIF lasers have a low rep rate, all lasters - present and future - will have a low rep rate." It may turn out that way, but I don't think the conclusion follows.

 

[Vanadium 50]

Maybe it''s best to think about what the ICF community is trying to do,.

First, we could have fusion today if we wanted to. You dig a deep hole, drop an H-bomb downb it, blow it up, and then use known geothermal power technology to extract the heat and turn it into electricity. When it cools off, dig another hole, and repeat. You can improve on this, but that's the ides.

This has a number of problems: it's not particularly cheap, it;s not particularly clean, and it's not particularly efficient. And maybe requiring a constant pipeline of nuclear weapons is not the smartest idea. But it is fusion, and we could do it today.

A lot of these problems go away if you can make your bombs smaller. Extracting the energy is more efficient. You can re-use the chamber where you do it. If your fuel is lost or stolen, it has only the energy of a couple sticks of dynamite, if the bad actors can even make it explode at all.

To make this work, you need to understannd the best way to make and use fuel pellets. You want to do this with simulation, because simulating a "shot"is a lot easier and cheaper than a physical shot. But to gain confidence in your simulation you need to tie it to data. The primary purpose of NIF is to get that data.

So it's not a case of spinning the wheels randomly and hoping to get a large energy output. It's not about seeing how fast you can go when you scale up. It's take a shot, think about it. compare it to prdictions, figure out what the next logical step is, take another shot, and so on. The most interesting data may or may not even be the ones with the highest yield. "You can't scale it up and make it commercial" misses the point that this is not intended to be a mini-commercial plant.

So of course NIF isn't running in a practical mode, It's job is to figure out where the practical operating point is. I suspect that absoluely everybody agrees that an H-bomb is too big and NIF is too small. But there's plenty of sparameter pace in between.

 

[PAllen]

...

First, we could have fusion today if we wanted to. You dig a deep hole, drop an H-bomb downb it, blow it up, and then use known geothermal power technology to extract the heat and turn it into electricity. When it cools off, dig another hole, and repeat. You can improve on this, but that's the ides.

This has a number of problems: it's not particularly cheap, it;s not particularly clean, and it's not particularly efficient. And maybe requiring a constant pipeline of nuclear weapons is not the smartest idea. But it is fusion, and we could do it today.
...

This might be fine if we blow up the bombs in the "right place".

 

[artis]

Sounds like practical use of fusion might have gone from 30 years away to 29 years...

That's actually quite good news since it's been stuck at 30 for the past 50.

Maybe that crypto guy in the Bahamas can chip in...

I hate to break it to you but "that crypto guy" will be 30 years away...

from 30 years away to 29 years

Only with good lawyers!

 

[BWV]

The other issue is the ~50% loss of energy using this to boil water to drive a steam turbine and the fact that neutrons will destroy the reactor over time

It may be anneutronic reactions like TriAlpha / TAE Tech, where the reaction generates charged particles that can be directly turned into electricity may be a better basis for a commercial reactor, but these reactions are more difficult

 

[artis]

Well NIF , from what I understand , basically just tests whether aged LithiumDeuteride and less than ideal T concentration can still function to spec within the secondary of a H bomb of the US stockpile.
But as @Astronuc for example already pointed out nicely in his calculation that with this method there is a long road to anything useful.

A lot of these problems go away if you can make your bombs smaller. Extracting the energy is more efficient. You can re-use the chamber where you do it. If your fuel is lost or stolen, it has only the energy of a couple sticks of dynamite, if the bad actors can even make it explode at all.

To make this work, you need to understannd the best way to make and use fuel pellets. You want to do this with simulation, because simulating a "shot"is a lot easier and cheaper than a physical shot. But to gain confidence in your simulation you need to tie it to data. The primary purpose of NIF is to get that data.

I think you have a good point here and it might just well be that the media are the ones hyping this up too much.
That being said I personally don't believe this approach can be practical no matter what.
Two large obstacles.

1)Lasers are rather inefficient in general, especially the ones they still use. Maybe semiconductor based lasers can increase the efficiency as they are generally quite more efficient although I can't comment on whether such will suffice for the power requirements and beam quality requirements for NIF.

2) This is probably the worst , the fact that the implosion can only be successful if it is near perfect in timing and symmetrical etc. Given these are fine tuned parameters for what is essentially a tiny sphere it means it will need mechanical changing while placing the next one in the chamber. This takes time. It also means the placing of each new pellet has to be very precise as offset would most likely damage the implosion symmetry and ruin the yield.
So at best I imagine they could do a "robotic arm" type of factory conveyor style thing where by some means they manage to change a new pellet in very little time but given I suppose the pellet needs to be precisely positioned , I would guess 1 Hz shot rate would already be sky high ...
That is if the lasers can keep up. At that power level it seems they can't.

And when speaking of efficiency, the gap is actually double , the heat to electricity conversion is around 33% and the laser electric input (as measured from grid) to light that reaches and implodes the target is what? 1% currently?
Just a late night curiosity without much thought, so they can't make the laser that more efficient now, they can't increase the repetition rate by much, but can they increase the pellet diameter and make a more efficient longer burning higher density plasma, aka increase the "triple product" ?
Or is the pellet size already optimal for the implosion they can achieve and increasing it's diameter would only worsen the fusion conditions?

 

[hutchphd]

So at best I imagine they could do a "robotic arm" type of factory conveyor style thing where by some means they manage to change a new pellet in very little time but given I suppose the pellet needs to be precisely positioned

It would have been difficult to imagine a Boeing 747 had you been on a Kitty Hawk Dune in 1903. Surely positioning the pellet is not an issue. However this does not trivialize repeated failures of a developing technology to thrive. Some avenues just don't work out. There are plenty of other extant and likely terminal issues.
Sufficiently advanced technology may well appear as magic to the uneducated, but that is not an endorsement for magic research.

 

[Vanadium 50]

Well, the requirement for fusion to be adopted in the West will not be "is it better than what we have right now" but "is it absolutely safe and absolutely clean? Not a single gram of waste? Not a single radioactive decay?"

 

[berkeman]

Thread closed briefly for Moderation...

 

[berkeman]

An off-topic subthread has been deleted, and the thread is reopened (that subthread may be posted as a new thread if the participants want to do that, most likely in the GD forum and not Nuclear Engineering).

Please remember to stay on-topic for this Fusion Announcement thread. Thanks.

 

[Astronuc]

Record Energetics for an Inertial Fusion Implosion at NIF (through 2020)
https://link.aps.org/accepted/10.1103/PhysRevLett.126.025001

Nice summary and some details on earlier trials before 2021.

The basic principle of ICF is to use a powerful driver
to rapidly compress the fuel to fusion-relevant temper-
ature and density conditions [3]. Most ICF approaches
pursue hot-spot ignition [4], in which the fuel is initially
layered cryogenically on the inner surface of a capsule.
The drive rapidly ablates the capsule material, imparting
inwardly-directed velocity in the deuterium-tritium (DT)
fuel layer, which stagnates at the center creating high
pressures in a central ‘hot spot’ created via compression
of the initial vapor and ablation of the inner fuel layer.
Hot-spot ignition has large theoretical fusion energy gains
if the fuel can be compressed symmetrically with low
entropy. Multiple driver schemes have been developed
including laser indirect drive, where the laser energy is
converted to x rays in a radiation cavity (‘hohlraum’),
laser direct drive [5, 6], and magnetic direct drive [7, 8].
Significant understanding of these challenges has been
developed at the National Ignition Facility (NIF)[9] for
the laser indirect drive approach, including successes in
implosion control that have led to net gain from the fuel
and significant yield amplification from self-heating [10–
15]. However, these implosions have reached limitations
short of the burning plasma regime [16], and the current
program is focused on improving performance towards
this milestone.

 

[artis]

So here are some details of why apparently this last shot was the most energy yielding of all the previous ones.
https://lasers.llnl.gov/news/high-quality-diamond-capsule-enhanced-nifs-record-energy-shot

From the reading I notice 2 main takeaways
1) Pellet outer layer (pusher /tamper) made out of synthetic diamond to reduce the layers impurities mixing with the fusion fuel once it reacts

The capsule had 10 times fewer surface holes, or pits, and subsurface voids, as well as fewer contaminating high-Z (high atomic number) inclusions, than the capsule used in NIF’s previous record-energy experiment in February 2021, which produced only one-eighth the energy of the August shot. The capsule defects were thought to substantially contribute to the amount of capsule material mixing into the imploding fuel, preventing it from being compressed properly and reducing the hot-spot fusion rate below that required for ignition.

Also they made the capsule/pellet outer layer feed hole smaller which is used for filling the inner void with DT mixture.

A tiny two-micron-diameter fill tube was used to inject deuterium-tritium (DT) fuel into the capsule, limiting the tube’s contribution to implosion instabilities. The February shot used a five-micron fill tube—itself much thinner than the tubes used in early NIF experiments, which ranged from 10 to as much as 44 microns in diameter.

2) They also decreased the size of the axial openings at each end of the "hohlraun" high Z cavity , the inner walls of which emit X rays after being bombarded with the UV photons from the lasers, this apparently minimized radiation leakage from the holhraum

A new hohlraum design with smaller laser entrance holes limited the loss of energy escaping through the holes during the implosion, improving hohlraum efficiency—the amount of energy coupled to the capsule—and enhancing the fuel compression and hot-spot pressure

Here is a video about it (also present in the upper link)

Here's one personal curiosity from me, those knowledgeable can maybe answer it.

It is known from literature (at least the open literature) that the "pusher/tamper" of a thermonuclear bomb secondary which is identical in principle to the NIF capsule/pellet outer layer is made from a high Z material in the H bomb case for various reasons but mainly so that the X rays that impact it don't go through to the fuel inside and cause pre heating of it. The material is opaque to the radiation to cause successful ablation without preheating of the fuel. The radiation temperature within the radiation channel therefore demand a high Z material.

In NIF case the outer layer is of low Z material. Could this be because NIF radiation is of much lower energy than that of a H bomb radiation case therefore the a low Z material suffices as opaque and preheating doesn't happen?

This is the first guess from me myself. A food for thought.

 

[Astronuc]

mainly so that the X rays that impact it don't go through to the fuel inside and cause pre heating of it. The material is opaque to the radiation to cause successful ablation without preheating of the fuel.

It's more the case that one wants the 'ablation' layer to absorb the maximum energy in order to maximize temperature in a as short a time as possible, so that it will ablate. High Z materials attenuate X-rays and electrons because the atoms have Z electrons. Light elements like H, Li, Be, B, C, N, and O do not attenuate radiation (electrons and X-rays) as well as higher Z elements like Ti/V/Cr/Fe/Ni/Cu, Zr/Nb/Mo, Hf/Ta/W or Th/U; the higher the Z, the more effective the attenuation. The added issue with U is the matter of fission, which would mean processing fission products after the shot would defeat the goal of producing energy without fission products.

Nevertheless, there will be plenty of activated (radioactive) elements in the system, since d,t produce n (14.1 MeV) and alpha (3.5 MeV), and those neutrons not absorbed in a Li blanket would be absorbed by the surrounding structural material(s), including the holder.

As part of my current research, I just happen to be looking at attenuation of gammas and electrons of the same energies in a variety of materials. Three observations are: 1) gammas are more penetrating than electrons of the same energy, 2) the higher the Z the greater the attenuation at a given energy, and 3) the higher the energy of gamma rays, the more likely they scatter in the forward direction.

Gammas (and X-rays) interact with atomic electrons by Thomson/Rayleigh scattering, photoelectric effect (absorption) or Compton scattering. Thomson/Rayleigh scattering and photoelectric effect dominate at low energies, while Compton scattering becomes more important as energy increases (> 100 keV) to a moderate range. As photon energy increases beyond 1.022 MeV (2*m_e), pair production becomes important, and the energy at which the probability of pair production equals that of Compton scattering depends on Z.

https://www.nde-ed.org/Physics/X-Ray/attenuation.xhtml
https://radiologykey.com/x-ray-imaging-fundamentals/

 

[sophiecentaur]

OK, if this were to pan out and become a viable source of energy, what would that do to all the schools now currently investing in hydrogen-energy research?

There are two separate issues here. Fusion is a potential source of carbon-free energy. This needs to be stored when wires are not long enough.
Chemical methods are favourite in many respects. There are many options for this. Batteries are convenient but require high mass and scarce chemicals. Carbon compounds would be convenient (IC engines) and could involve no net carbon production if they were made from electricity. But there could / would be local pollution.

BUT Hydrogen could be used in fuel cells and / or IC engines and produce only waste water. There is no present method (afaik?) that would make small scale (cordless appliances) Hydrogen energy storage practicable. So we could be stuck with IC engines or batteries for some while for many purposes.