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US Department of Energy: Fusion Ignition Achieved

energy.gov

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Re: US Department of Energy: Fusion Ignition Achieved

#931

Post by moloch-hai »

kennend3 wrote: post #924
moloch-hai wrote: post #792

Earlier quoted context omitted.

It will happily fuse further. It just won't support the outside of a star against gravity, while doing it. So the star collapses, fuses lots more stuff even heavier than iron, and then explodes. Most of the iron and heavier stuff fuses into the core of a neutron star, the ultimate in energy-consuming fusion.

None of this is accurate. Iron will not happily fuse further because this NEEDS energy and where would that energy come from? "heavier than iron" elements are produced when a star explodes because that collapse produces enormous amounts of energy. During the collapse, the outer edge of the star is accelerated to something like 20% of the speed of light, that is an ENORMOUS amount of energy slamming down on the core.…

You answer your own question: the energy for further fusion, all the way to neutron degeneracy, is provided by gravitational collapse. The outer layers fusing provide energy for the explosion.

Re: US Department of Energy: Fusion Ignition Achieved

#932

Post by bzbarsky »

epgui wrote: post #929
eru wrote: post #793

Earlier quoted context omitted.

> [...], or the ginormous fusion of the sun. The sun actually has very little fusion per cubic metre or per kg. Per volume the core of the sun produces only a quarter of the heat of the human body (and per kg it's even less, owing to high density). That's why our fusion reactors can't just mimic stars, they have to far surpass them to be useful to us.

The per-volume claim rings alarms in my head. If it produced a quarter of the heat of the human body per volume, its temperature would be lower as well (less than 37 degrees Celsius).[1] This is obviously not the case. [1] Obviously heat and temperature are not the same, I know that. But when something’s temperature is higher than another thing’s, then heat is exchanged along that gradient. Meaning if the sun produce…

Heat and temperature are indeed not the same.

For both the sun and a human on earth there are two processes going on:

1. Heat production per unit volume.

2. Heat loss per unit surface area.

The volume to surface area ratio for the sun is much larger than for the human, for a minor reason (the sun is a sphere) and a major reason (the sun's linear size is much bigger). So the equilibrium temperature of the sun in the same ambient outside environment is higher than the human's.

Your thought experiment about placing a human inside the sun would in fact work as you say, if a human body continued to produce heat once it had achieved thermal equilibrium with the surrounding plasma.

Re: US Department of Energy: Fusion Ignition Achieved

#933

Post by metadat »

speeder wrote: post #911
_cs2017_ wrote: post #771

Earlier quoted context omitted.

How would it help build better weapons? I thought the existing thermonuclear bombs do the job perfectly fine. Sure, the military might want to make them a bit smaller or a bit cheaper, but is it really such a big deal as to warrant a major announcement?

I guess they also don't want to blow up random civilians by accident again. When castle bravo was tested, we didn't knew that lithium7 fusion was possible and that it would generate energy. The bomb had a lot of lithium7 because it was cheaper than lithium6. Castle Bravo then proceeded to explode with way more power than intended, it vaporized the measurement instruments, ruined the test site, damaged civilian proper…

More on Castle Bravo: https://en.wikipedia.org/wiki/Castle_Bravo

Re: US Department of Energy: Fusion Ignition Achieved

#934

Post by gene-h »

afpx wrote: post #907
gene-h wrote: post #525

Earlier quoted context omitted.

It will be quite difficult to make fusion cheaper than present day fission. Fusion reactors are new so significant research work will need to be done. There are difficult engineering challenges related to breeding fuel, which involves moving hot, radioactive, and water reactive molten lithium around. Fusion reactors need to be built to high tolerances and will need to be refurbished occasionally due to radiation/heat…

50 years from now, are we going to be using fission or fusion?

Hopefully, both. Even if fusion works extremely well, fission should find niches. Fission power is likely to remain more power dense than fusion for a while, so in situations where one cares about weight and size it is better than fusion.

Re: US Department of Energy: Fusion Ignition Achieved

#935

Post by thehappypm »

iamgopal wrote: post #764
opportune wrote: post #584

Earlier quoted context omitted.

100% agree. We should be dumping as much as we can in getting fusion up and running ASAP. It could be a silver bullet to stop climate change alone, and by driving energy costs lower, enable huge innovations in AI/automation and increasing material wealth. $1T to move fusion forward just 5 years from eg 2040 to 2035 could alone have a huge ROI in terms of climate mitigation and decarbonization

How easy is to write $1T, but with that you can basically install enough solar cell to power all of USA energy need.

Fusion can give us 10x our energy need. Imagine a world where energy is simply not a blocker for anything.

Re: US Department of Energy: Fusion Ignition Achieved

#936

Post by bzbarsky »

cloudhead wrote: post #885
eru wrote: post #793

Earlier quoted context omitted.

> [...], or the ginormous fusion of the sun. The sun actually has very little fusion per cubic metre or per kg. Per volume the core of the sun produces only a quarter of the heat of the human body (and per kg it's even less, owing to high density). That's why our fusion reactors can't just mimic stars, they have to far surpass them to be useful to us.

How is the sun so hot then?

Total power radiated by a black body per unit surface area scales as T^4 (in Kelvin).

So for black bodies with identical shape and linear dimensions R1 and R2, with identical power production per unit volume, both in thermal equilibrium with whatever is outside them, you would expect:

R1/R2 = (T1/T2)^4

(because setting power produced equal to power radiated gives R proportional to T^4).

Pretending humans are spheres with radius 1m and the sun is a sphere with radius 7*10^8m, you would expect the sun to have ~160 times the temperature of a human at equilibrium in vacuum. It's going to be lower because not all of the sun is power-producing, of course. But higher because a human is not 1m in radius. And again higher because humans are not spheres and lose heat more than a sphere would for the same volume (more surface area).

The sun is about 6000K on the surface. That would give us ~40K for the equilibrium temperature of a human in vacuum, which at least seems truthy.

TL;DR: the sun is big, with a small surface area compared to its volume, because it's big.

Re: US Department of Energy: Fusion Ignition Achieved

#937

Post by dr_dshiv »

PaulHoule wrote: post #921
eru wrote: post #832

Earlier quoted context omitted.

To give some more detail: hydrogen to helium fusion (even with intermediate steps) is extremely unlikely to happen. That's part of why the sun will last for billions of years. And that's also why first human attempts at fusion are not trying to use straight up hydrogen as the fuel. Good old Wikipedia has this gem: > The large power output of the Sun is mainly due to the huge size and density of its core (compared to…

Those Fusors can make a decent neutron source however. Those were invented by Philo Farnsworth, who invented the cathode ray tube for television.

I’m so disappointed I can’t just buy a fusor online.

But here is a MAKE magazine article explaining how to build! https://makezine.com/projects/nuclear-fusor/

Re: US Department of Energy: Fusion Ignition Achieved

#938

Post by njarboe »

bunabhucan wrote: post #806
_cs2017_ wrote: post #771

Earlier quoted context omitted.

How would it help build better weapons? I thought the existing thermonuclear bombs do the job perfectly fine. Sure, the military might want to make them a bit smaller or a bit cheaper, but is it really such a big deal as to warrant a major announcement?

"Nuclear stockpile research" is only making weapons "better" in the sense that they are reliable despite not having been tested in decades. There's probably a component of "unemployed nuclear weapons designers is a bad thing" also. The fusion for power experiments are using the same laser equipment but different targets and sensors.

The DOD also probably likes having some nuclear weapons designers available on short notice

Re: US Department of Energy: Fusion Ignition Achieved

#939

Post by chaosbolt »

quickthrower2 wrote: post #848
gfodor wrote: post #185

Another good time to remind everyone that the inventor of the maser (which led to the laser), Charles Townes, was discouraged by his department chair (allegedly): "Look, you should stop the work you are doing. It isn't going to work. You know it's not going to work, we know it's not going to work. You're wasting money, Just stop!" A few months later, it worked. [1] [1] https://www.theregister.com/2015/01/29/charles_t…

> He later explained that he was able to refuse to stop his research because he had tenure, so there was nothing they could really do to stop him. Not having to chase your next meal can make a big difference

Exactly, this is the biggest problem with modern universities.

I wish billionaires would fund things like this directly as in no patent no nothing, just from the goodness of their hearts, which they claim is there seeing how much they all pledge to charities... But the reality is different, Oxford pledged to donate the rights to their covid vaccine for free then was urged by the bill & melinda "foundation" to reverse course and sold it to pharma companies.

Re: US Department of Energy: Fusion Ignition Achieved

#940

Post by dahfizz »

iamgopal wrote: post #764
opportune wrote: post #584

Earlier quoted context omitted.

100% agree. We should be dumping as much as we can in getting fusion up and running ASAP. It could be a silver bullet to stop climate change alone, and by driving energy costs lower, enable huge innovations in AI/automation and increasing material wealth. $1T to move fusion forward just 5 years from eg 2040 to 2035 could alone have a huge ROI in terms of climate mitigation and decarbonization

How easy is to write $1T, but with that you can basically install enough solar cell to power all of USA energy need.

. $1T doesn't buy nearly enough batteries for the storage we would need.

We should be installing more solar & wind, but that alone is not a solution to our problems.

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