But ITER is the worst possible fusion project. I mean no offence, but ITER makes nuclear reactors look cheap and small. (well, granted, the actual reactors are small, but I'm talking about the support infrastructure too)
Frankly, if ITER has the scaling laws of Tokamaks right, there won't ever be a working Tokamak smaller than a 10 story building, or producing less than about 1.5 GW. And q values can go up to maybe 10, not counting generator losses. To be honest : we don't want that.
Getting this refunded basically means that more money is going to various other fusion ideas, and that's much better than having all our eggs in one hugely expensive, massively unwieldy and "just 10 more years" project (just 10 more years for about 40 years now).
Frankly, ITER is one of those huge failed projects that just won't admit failure for mostly political reasons. We all know about lots of them. Either it will fail directly because physics somehow prevents Tokamaks from being cost effective, or it will fail because it won't succeed by the time we need it to succeed. So far, the net result of the project is that a 6 story Tokamak can't work, due to plasma instabilities. So they're building a 10 story one.
The project itself has stupendous accomplishments. It has demonstrated almost unprecedented international scientific collaboration. The amount of money freely given to fund ITER is ridiculous. The amount of companies collaborating with academics on it is in the hundreds. It has so many governments invested in it ... It has so many committees and university boards invested in it it's hard to find a decent physics department that isn't invested in it ... but all of these are political achievements. The physics side of the project is finding physics not all that cooperative.
You should think about what ITER is trying to do as a way to apply massive force to reality until it bends to our will. It's not smart at all (of course the details of doing this are very intricate. There's a difference. Smart is finding a way to beat the calculation speed of a huge datacenter with a 1990's pentium when it comes to calculating digits of pi [1]. Intricate is building a huge datacenter. Both are great accomplishments, of course).
The problem with most of the other projects are facing is that they violate "holy cows" of physics in some way. Polywell physics require a very low-pressure non-thermalized gas, which has been demonstrated but violates thermodynamics theory. It's never going to get past more than one or two physics boards. Z-pinch is one of those tricks that's just too good to be true if it works (it does work to some extent of course). Like polywells, it's a huge risk, so getting physics professors to bet their careers on it is a non-starter. Laser fusion (and other forms of inertial confinement fusion) has similar "WTF" parts that will prevent their widespread acceptance. Because most of these things have multiple projects running, in practice this is about 12 projects.
All fusion projects, with 2 exceptions (one of which is strongly suspected to be a fraud), are happening inside America, funded by either the DoD or DoE. Each of them has a much lower chance of success than ITER, I would agree with that, but if they do succeed, the payoff will be much greater. If polywells work, for example, we should be able to build a 100 megawatt or so fusion reactor the size of a 60s TV set, that could operate in a building that needn't be bigger than a big house. You know, easily small and efficient enough to install on even medium sized ships. Hell, you could probably power planes with it. None of the projects even approach the size and inefficiency of ITER (meaning 10 stories, maximum achievable q value of 10 or lower). ITER should be shelved as "not good enough" and people should go back to the cafe napkin stage.
> Also, you can't make small scale fusion power plants. If the reactor was the size of a light bulb and produced 40w of power you would still need several feet of shielding to avoid killing anyone in the area and that shielding would vary quickly become extremely radioactive. Fission is low energy in comparison. http://en.wikipedia.org/wiki/List_of_coal_power_stations over 5+ GW of thermal power.
Google "aneutronic fusion". Granted, ITER will never support it, but that's just another reason to try other things. ITER makes everything radioactive, but aside from that being the easiest reaction there is no good reason for doing that.
As for the size of fusion reactors, go to your nearest (big) hospital. They have a football-sized one in the radiology department. The box it's in is fridge-sized. A Farnsworth-Hirsh fusor to be exact. It will be shielded, because it's using DT fusion. If you really knew what you were doing you could get it to fuse p+B11 and it would produce electrons, but it would defeat the point for the hospital, as it's neutron radiation is exactly why they have it.
Now granted this reactor has a q value of 0.02 or so. But if there were a smart way to get it to a q of 100 or so that would almost be your lightbulb example. Get it to work on p-B11 and ...
There is no such thing as neurotic fusion. Best case neutrons carry 1% of the total released energy, but if a 100w light bulb produced 1w of unshielded 2.5MeV neutrons it would quickly give everyone in a fairly large room a lethal radiation dose.
Edit: For the morbidly curious 1w / (3 x 10 -13)j/electron = 3.3e+12 electrons. 10M from the device you have a sphere with a surface area of 1256m^2.
http://miscpartsmanuals3.tpub.com/TM-55-315/TM-55-3150021.ht... 1 rem (neutrons/cm2) from 2.5 MeV neutrons = 3* 10^6 neutrons / cm^2. 100 rem received over a short time period are likely to cause acute radiation syndrome (ARS), possibly leading to death within weeks if left untreated. So, 3 * 10^6 * 100 * 100^2 * 1256 = ~4 * 10^ 15 electrons would kill ~1/2 the people standing within 30 feet in ~10 minutes. And far less time than that to start handing out cancers left and right. And at 10 feet that's ~60 seconds. (Assuming I did not mess up...)
PS: It's far safer to spread the same dose over longer periods of time. But, if your working near a useful fusion device it needs to be heavily shielded.
They are harder to initiate than the D-T reaction, which is why they're not the ones being tried first for fusion-generated electricity; but they're perfectly good fusion reactions which have been observed in experiments.
There are fusion paths that don't result in neutrons but you don't get to limit yourself to just those path's. Consider DD fusion > 50%He + 50%T but you don't get to keep the T in a thermal DD plasma so you need to also look at DT's paths.
proton-whatever also gives you some proton-proton fusion so now you have deuterium which is not so clean. Let alone p whatever the walls of your chamber are.
Still, if your going to pretend we can do anything harder harder than DT or perhaps DD your might as well go for p+p as it's fairly 'clean' and the fuel is plentiful.
p+p is a lot harder to initiate than any of the reactions listed on the Wikipedia page I linked to. The only reason it happens in stars is that gravitational confinement makes stellar cores much, much denser than plasmas we can produce on Earth. It's not going to happen in an Earthbound reactor using proton (+ something else) fuel.
You're right that there will be some fuel particles that escape confinement and react with the chamber walls; but proper confinement makes this effect very small, much smaller than the numbers you were quoting for radiation exposure, which are based on using fuels that produce neutrons as reaction products. Neutron's can't be confined in a plasma because they're uncharged, so they immediately escape and hit the chamber walls. Protons, and other fuel particles, don't have that problem since they're charged and can be confined (if they couldn't be you wouldn't be able to make the reactor work at all).
It's not just particles directly causing reactions by hitting the walls they also cause sputtering which contaminates the plasma with whatever the wall was made out of. As to PP fusion you get some in any vary high energy plasma probably not enough to be useful for power generation but enough to make some D. Not to mention your fuel is hardly going to be pure in the first place.
Which gets back to my first point you can have low nitron fusion but if your generating useful amount of power your going to be makeing significant amounts of neutrons simply because there so deadly.
> As to PP fusion you get some in any vary high energy plasma
Do you have a reference for this? As I understand it, there aren't significant amounts of protons in our current plasma experiments to begin with, and at the densities we use in those experiments, the cross section for p-p reactions is way too small for them to appear.
> if your generating useful amount of power your going to be makeing significant amounts of neutrons
For current and foreseeable reactors, I agree; but I don't think this is a valid blanket statement about every possible type of fusion reactor that could ever be built, even when our technology has advanced well beyond where it is now.
By some I mean it happens not that it's a significant reaction. PP fusion is in no way a useful approach until you run out of everything else and still want power. Still the sun is 1/10th of ITER's goal temperature so your well in the range for PP fusion based on however much contaminates the plasma.
As to the long term potential I don't think we can rule it out in the longer term, just that when people talk about fusion without neutrons they mean low levels or don't actually know what there talking about.
And I'm asking if you have seen any actual evidence that it happens. I have not, and the information I have seen, which I mentioned, leads me to believe that it should not have happened in any fusion experiments we've done to date. That's why I asked you for a reference.
> the sun is 1/10th of ITER's goal temperature so your well in the range for PP fusion
No, the ITER is not "in the range for PP fusion", because temperature is not the only requirement. You also need sufficient density. The density in the Sun's core is many orders of magnitude larger than the density of plasma in ITER or any other Earthbound fusion experiment. That has a huge effect on the PP reaction cross section.
The rate of fusion changes as the square of density but you still get fusion at vary low density's it's just less common. You might be thinking of fission?
As to PP fusion from what read. Without a large enough plasma the beta more common proton emission path >99.99% ends up costing more energy than you gain from beta-plus decay <0.01%. "The least stable is 5He, with a half-life of 7.6×10-22 seconds, although it is possible that 2He has an even shorter half-life" http://en.wikipedia.org/wiki/Isotopes_of_helium#Helium-2_.28...
The rate of fusion changes as the square of density but you still get fusion at vary low density's given sufficient energy it's just less common. You might be thinking of fission?
As to PP fusion from what read. Without a large enough plasma the beta more common proton emission path >99.99% ends up costing more energy than you gain from beta-plus decay <0.01%. "The least stable is 5He, with a half-life of 7.6×10-22 seconds, although it is possible that 2He has an even shorter half-life" http://en.wikipedia.org/wiki/Isotopes_of_helium#Helium-2_.28...
> The rate of fusion changes as the square of density but you still get fusion at vary low density's given sufficient energy it's just less common
How much less common? Again, have you seen any actual evidence that P-P fusion events actually happen in actual Earth-bound plasmas? Because the numbers I've seen indicate that at Earth-bound plasma densities, such events are so unlikely that we should not expect to have observed any.
http://www.sns.ias.edu/~jnb/Papers/Preprints/Solarfusion/pap... "the rate for the fundamental p1p?2 D1e11ne reaction is too small to be measured in the laboratory. Instead, the cross section for the p-p reaction must be calculated from standard weak-interaction theory." Considering the solar density's are ~10^11 times as high as steady state fusion experiments on earth we are looking at ~1/10^22 as many reactions so you might be right that beta-plus decay of deuterium may not have happened in the lab but PP fusion into deuterium is far more common.
PS: And thanks for this, it's good to be called out on something like this. I tossed out the PP comment without thinking though simple contamination is a far larger source of high energy neutrons.
> beta-plus decay of deuterium may not have happened in the lab but PP fusion into deuterium is far more common
It looks to me like the comment about the rate being too small to measure in the lab applies to the PP fusion into deuterium; that's the reaction referred to in the statement you quote. The positron that's produced is not a "beta-plus decay of deuterium"; it's a product of the PP fusion into deuterium, part of the same overall reaction.
Frankly, if ITER has the scaling laws of Tokamaks right, there won't ever be a working Tokamak smaller than a 10 story building, or producing less than about 1.5 GW. And q values can go up to maybe 10, not counting generator losses. To be honest : we don't want that.
Getting this refunded basically means that more money is going to various other fusion ideas, and that's much better than having all our eggs in one hugely expensive, massively unwieldy and "just 10 more years" project (just 10 more years for about 40 years now).
Frankly, ITER is one of those huge failed projects that just won't admit failure for mostly political reasons. We all know about lots of them. Either it will fail directly because physics somehow prevents Tokamaks from being cost effective, or it will fail because it won't succeed by the time we need it to succeed. So far, the net result of the project is that a 6 story Tokamak can't work, due to plasma instabilities. So they're building a 10 story one.
The project itself has stupendous accomplishments. It has demonstrated almost unprecedented international scientific collaboration. The amount of money freely given to fund ITER is ridiculous. The amount of companies collaborating with academics on it is in the hundreds. It has so many governments invested in it ... It has so many committees and university boards invested in it it's hard to find a decent physics department that isn't invested in it ... but all of these are political achievements. The physics side of the project is finding physics not all that cooperative.
You should think about what ITER is trying to do as a way to apply massive force to reality until it bends to our will. It's not smart at all (of course the details of doing this are very intricate. There's a difference. Smart is finding a way to beat the calculation speed of a huge datacenter with a 1990's pentium when it comes to calculating digits of pi [1]. Intricate is building a huge datacenter. Both are great accomplishments, of course).
The problem with most of the other projects are facing is that they violate "holy cows" of physics in some way. Polywell physics require a very low-pressure non-thermalized gas, which has been demonstrated but violates thermodynamics theory. It's never going to get past more than one or two physics boards. Z-pinch is one of those tricks that's just too good to be true if it works (it does work to some extent of course). Like polywells, it's a huge risk, so getting physics professors to bet their careers on it is a non-starter. Laser fusion (and other forms of inertial confinement fusion) has similar "WTF" parts that will prevent their widespread acceptance. Because most of these things have multiple projects running, in practice this is about 12 projects.
All fusion projects, with 2 exceptions (one of which is strongly suspected to be a fraud), are happening inside America, funded by either the DoD or DoE. Each of them has a much lower chance of success than ITER, I would agree with that, but if they do succeed, the payoff will be much greater. If polywells work, for example, we should be able to build a 100 megawatt or so fusion reactor the size of a 60s TV set, that could operate in a building that needn't be bigger than a big house. You know, easily small and efficient enough to install on even medium sized ships. Hell, you could probably power planes with it. None of the projects even approach the size and inefficiency of ITER (meaning 10 stories, maximum achievable q value of 10 or lower). ITER should be shelved as "not good enough" and people should go back to the cafe napkin stage.
[1] http://bellard.org/pi/
reply