Are fusion power plants feasible for widespread use?

[Kidphysics]

Imagine the following design:
· ions source,
· then the coaxial chamber filled with gas (neutralizer),
· then the separation chamber magnetically declining particles (ions) still remaining charged while neutralized particles keep stright direction
· then the long pipe called in Russian "atomoprovod" ("atom conductor")
· then reaction chamber (vacuum chamber)
Atom conductor is equipped with deposited surface gas adsorbers keeping vacuum at acceptable level for certain (not long) time. As you can see that the chamber filled with gas is connected directly with vacuum chamber. Adsorbers are cooled to cryogenic temperatures.
And after each shot experimentators are forced to desorb those adsorbers by heating.
Such a design is acceptable at experimental level but impractical for real fusion reactors.
And as far as I know there is not any different NBI design.

For sure JET has them and so does ITER...

 

[Joseph Chikva]

For sure JET has them and so does ITER...

As far as I know all neutral beam injection (NBI) have described above design. And I am claiming that such design is impractical and less useful for commercial reactors.

From another side NBI is the most effective heating way at temperatures exceeding 1 keV.
The second application of NBI is to drive current (the so called "beam driving current") that converts TOKAMAK into "advanced" or "H-mode" or "high confinement mode", without which it is impossible to achieve minutes order confinement times already achieved in TOKAMAKs.

So, as you can see TOKAMAKs today also are not ready for commercialization.

I have one idea how to avoid nessecity of NBI in TOKAMAKs.
I think that at first we using TOKAMAK field configuration (the combination of poloidal and toroidal fields) can easily create in-situ in the reaction chamber the halo-layer of high energetic (several MeV) particles.

For this we have to performed consistently the following procedures (corresponding hardware should be included in toroidal fusion reactor):
• orthogonally to equatorial plane of toroidal vacuum chamber to create generally the time-dependent magnetic field (bending field) penetrating only its curvilinear segments,
• to apply axial (toroidal) magnetic field only in the regions located remotely from injection points,
• along the axis of toroidal vacuum chamber to inject 3 different kinds of pulse high current particle beams (two ions’ – reacting components and one – electron’s) with such a parity of particles’ kinetic energies allowing them the capability of moving in a given bending magnetic field on a common equilibrium orbit (gyro-radiuses (rg=p/qB) of all 3 spices are equal) in such a manner that faster ion beam passes through the moving at the same direction slower ion beam with sufficient for nuclear fusion collision energy and the relativistic electron beam moving oppositely to ions thus allowing to combined beam the self-focusing capability,
• to apply axial (toroidal) accelerating electric field compensating the occurring together with fusion two effects: tendency of alignment of velocities of reacting particles and also electrons’ energy losses via Bremsstrahlung.
(G.I. Budker says that number density up to 10^24 m^-3 and even higher is achievable in combined beam and as result of fusion the high energetic fusion products are produced, from which neutrons escape reactor while charged particles form halo-layer.)

Then once as result of fusion we create the halo-layer only then to create the plasma.

For this we have to do the following:
• from the walls with the help of corresponding valves to puff into the vacuum chamber the gas consisting the fuel components. And already being there halo-layer ionizes that gas and then generates the current similarly to that how current is driven by beam/beams of neutrals in modern TOKAMAKs.
• in regions being free from axial magnetic field to apply such a field at once after the end of injection.

And I am sure that this idea would make TOKAMAKs viable for commercial application right now.
As despite all other approaches the theory of TOKAMAKs is really well developed.

 

[JimmyTrow]

Lawrenceville Plasma Physics

Noticeably absent in these discussions are the efforts of the people at LPP. By some measures they are the leaders in the attempts to commercial fusion. To date they have made the most progress with the least resources and are largely ignored. They publish semimonthly updates on their progress and are interesting to follow. Their approach is somewhat different. Their reactor is a pulsed affair and relies on the very instabilities which plague other approaches to achieve a strong electromagnetic pinch. Which (in theory) should arrive at sufficient density to achieve ignition. They already have sufficiently high temperatures, and adequate confinement time.

 

[Joseph Chikva]

Noticeably absent in these discussions are the efforts of the people at LPP. By some measures they are the leaders in the attempts to commercial fusion.

Nobody today is close to the desired goal. Including "people at LPP". And first problem is in lack of interest of decision making people.
As at least initially fusion will not have economical advantage against fission. From another side fission is already well developed, while fusion needs many billions for its development.

 

[JimmyTrow]

I'm sure you are right on all accounts. You must be following them far more closely then I am. Still, the fact that they are getting about 1/3 joule fusion per shot shows some progress.

 

[the_wolfman]

I'd be very careful. I suspect that the fraction of a Joule of fusion energy that LPP is reporting is probably not net energy gain, but rather the total amount of energy release by fusion. It is still a promising result for dense plasma focus devices. However, it is fairly easy to create fusion. The difficulty is creating more energy out than energy in.
For comparison in 1997 the Joint European Tokamak (JET) generated 22 MJ of fusion power.
About 60 million times more energy than reported for the DPF device.

 

[JimmyTrow]

Noted Wolfman. They need 66 kJoules net fusion for this to work. I do think they have the best chance of any approach I've read about since I started following fusion in 1965. That's per shot.

 

[Toast]

Roadmaps to achieving commercial fusion have been published. The plan in Europe is to build a large Demonstration power plant (DEMO) device extrapolated from ITER https://www.euro-fusion.org/wpcms/wp-content/uploads/2013/01/JG12.356-web.pdf

Other ideas include smaller more compact spheromaks which would be quicker and cheaper to build but require more advanced plasma physics

 

[Freemann]

PS #2: Are you sure that first commercial fusion power plants will produce cheaper energy than for example fission plants? If to recall that fuel cycle’s cost share in total production cost of 1 kW*h is not so significant for fast neutrons plants. Are you waiting revolution and total happiness at once after achievement of break-even in any fusion approach?

Although a "competitive cost of electricity" is not a mandatory requirement for the step beyond ITER, i.e. DEMO, I guess no one will be interested do design and build a demonstration reactor that is not giving a couple of hundres of MW with a reasonable availability and reliability for a price that will not be similarly to the current fission reactors.

A decade ago studies (e.g. PPCS) stated to run DEMO at an electricity cost similar to wind power. Too optimistic to my taste, but by the own definition of the project, DEMO shall demonstrate the economic feasibility of fusion, contrarily to ITER that shall demonstrate "only" the technical feasibility.

 

[sciencegeek777]

Fusion and Fission are complementary processes that take place in the sun. It is Fission that produces energy in the form of heat and light that we see. To create energy from fusion you must have fission, else you are never going to get more energy out than you put in. The sun is also very massive thus the reason why it can produce so much energy for such a long time. Mass is slowly released by the sun into space in the form of heat energy, thus there is a limit to how much energy you can create E=MC^2.

 

[PeterDonis]

Fusion and Fission are complementary processes that take place in the sun. It is Fission that produces energy in the form of heat and light that we see. To create energy from fusion you must have fission, else you are never going to get more energy out than you put in.

I have no idea where you are getting this from, but none of it is correct.

 

[anorlunda]

I have no idea where you are getting this from, but none of it is correct.

It sounds like he is trying to take the design of a thermonuclear warhead and applying that to a star. As you say, none of it is correct.

 

[Astronuc]

The sun is also very massive thus the reason why it can produce so much energy for such a long time.

Actually, this part is correct. The rest is nonsense. Fission (of heavy metal like Th, U, Pu) is not part of the process in the sun.

See articles on proton-proton fusion and CNO cycle.

http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/procyc.html#c1 - predominant in the sun.

http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/carbcyc.html#c1 (CNO cycle)

While this process is not a significant part of the sun's fuel cycle, a star like Sirius A with somewhat more than twice the mass of the sun derives almost all of its power from the carbon cycle. The carbon cycle yields 26.72 MeV per helium nucleus.

The processes used in the sun cannot be used on Earth, since the pressures are too great. Instead, we deploy d+d or d+t, or possibly d+³He or d+¹¹B, each of which are easier than the solar processes, but nevertheless difficult to achieve.

 

[Alex A]

@sciencegeek777 ,

Fission and fusion are the compliments of each other. Where one releases energy, the reverse process must consume it. The piece of the puzzle you are missing is called "The curve of binding energy". To make power you don't try to fission and fusion from the same end. Iron-56 is the most stable nucleus, and other nuclei rearranging to produce something closer to Iron-56 has the potential to release energy.

So light elements fusing releases energy. Very heavy elements fissioning release energy.

Binding energy is also a much tighter limit for energy production. MC^2 works if you also have antimatter.

 

[cmb]

I have no idea where you are getting this from, but none of it is correct.

Well, technically there is some truth to it, but it's wrong in the generality depending on how the word 'fission' is used.

Deuterium and tritium fusion, for example, consists of fusing those two isotopes to helium 5, which then fissions to a neutron and helium 4.

'Fission' is a plain english word meaning to break into parts. However, in nuclear physics, 'Fission' may be a title reserved for the fission of heavy element actinides.

There are non-fissioning fusions which are mediated by a different force. Where fusions result in a prompt fission of an unstable intermediate, these are mediated by the strong-nuclear force. On Earth we can only aim to perform fusion for energy via strong-force mediated fusion, because this produces fission fragments that are 'hot' (have kinetic energy).

There are fission reactions mediated by the electromagnetic force (for example carbon 12 and a proton, a step in the CNO cycle produces only a 1.95MeV gamma photon and the resultant nitrogen 13 does NOT fission). This is useless on Earth because the gammas cannot be captured by any efficient means. The Sun can do it because it's so big, the photons get to heat up the solar mass on their 100,000's mile journey outwards.

There are fission reactions mediated by the weak force, this is the case for the proton-proton fusion, in which two protons momentarily fuse then (ordinarily) just separate (difficult to know if there is actually a helium 2 formed or not, might just be a 'scattering' event) but every so often very very rarely in statistical terms, one of the protons decays to a neutron just at the moment of the fusion and leaves behind deuterium. The emission of the positron and electron neutrino from this fusion event is not regarded as a 'fission' which is usually confined to where multiple massive nucleonic products emerge form the nucleus, carrying away the excess energy as kinetic energy (which can then 'heat something up'). We can't do this on Earth because the reaction rate for weak mediated reactions is so poor it is literally impossible here, one needs a super dense and massive stellar core to do it, there is no other way, and like electromagnetically mediated fusion it still would not produce any thermal products.

Curiously, the very first ever 'controlled' fusion was the proton-lithium 7 fusion (14 Apr 1932 at Cavendish Laboratory by Rutherford/Cockroft/Walton), which results in the unstable beryllium 8 that fissions into two alpha particles. At the time this p-7Li fusion was, and still is often, reported and referred to as 'splitting the atom' rather than 'fusing atoms'.

So actually 'fission', in the technical sense (it is a proper word in its own right, fission means to break into parts), is a part of strong-force mediated fusion and is what we have to do on Earth for usable power here (if it is possible at all).

However, this is a subject of disambiguation because more often than not, in some circles, 'fission' is used as a title (rather than the english meaning) which is then reserved exclusively for the fissioning of heavy elements of the actinide series, in which a larger nucleus will break into two other substantial fractions of the nucleus, plus an assortment of 'debris', including neutrons (which can then cause the fission of more of the heavy nucleii).

Back to the point the contributor made, actually, oddly enough, of all the many nuclear fusion reaction types in the Sun, there are only a very few fusions that results in the fission of an intermediate, and these are all part of the CNO cycles, such as p+15N->12C+4He. One might argue that CNO is not even 'essential', as our Sun is mainly a pp fusion reactor, but it does happen.

The dominant cycle, the pp cycle, contains no strong-force mediated fusions (i.e. no fissioning intermediaries).

One curious feature I am interested in is that no solar fusion processes produce any neutrons, not even as intermediaries. I am unclear why that is, whether it 'just is like that' or if there is some actual reason and rational explanation.

So if we wanted to really do what the Sun does, we'd use electromagnetically mediated fusions and capture gamma rays for heat, but we can't so we use other reactions that the Sun doesn't do, and produce neutrons instead.

In answer to the original ancient OP question from 2013, there might be a simpler answer to it; maybe controlled fusion power is simply not feasible, hence that is the problem. It's an experiment running for over 70 years now, which must be the longest running science experiment ever (and might always be) that people haven't yet formed a negative conclusion on. Edward Teller famously (or infamously) said at a meeting at the Princeton Gun Club Feb 27, 1958, that magnetic confinement fusion was impossible because it required concave magnetic fields in all directions away from a confined plasma, which is impossible. His hypothesis (on magnetic confinement fusion) has yet to be disproven.

 

[PeterDonis]

technically there is some truth to it

Where? I see nothing whatever in what I quoted from your post that is correct. Fission does not take place in the Sun, and fission is not required to get net energy from fusion.

Deuterium and tritium fusion

Is not what happens in the Sun. Nor is it the only possible fusion reaction.

consists of fusing those two isotopes to helium 5, which then fissions to a neutron and helium 4.

Please give a reference for this statement. (Even if it is true, it does not show that any fusion reaction must involve fission, which is what you claimed.)

There are non-fissioning fusions which are mediated by a different force. Where fusions result in a prompt fission of an unstable intermediate, these are mediated by the strong-nuclear force. On Earth we can only aim to perform fusion for energy via strong-force mediated fusion, because this produces fission fragments that are 'hot' (have kinetic energy).

Do you have a reference for any of this, or is it just your personal theory about how fusion works? (Please note that personal theories are off limits for discussion here at PF.)

There are fission reactions mediated by the electromagnetic force

What are you talking about? The strong force is involved in any fusion reaction.

There are fission reactions mediated by the weak force

Same question here.

I don't see the point of commenting further on the rest of your post unless and until you respond to the above.

 

[cmb]

Do you have a reference for any of this, or is it just your personal theory about how fusion works? (Please note that personal theories are off limits for discussion here at PF.)

Yes, of course, this is given in standard texts, I will find a reference.

I think you might have misread some of what I wrote, or I was unclear in some way.

 

[PeterDonis]

I think you might have misread some of what I wrote

Possibly I have. If you can give a reference to a standard text that will help to ground the discussion.

 

[cmb]

Possibly I have. If you can give a reference to a standard text that will help to ground the discussion.

I have a chapter from an electronic book from a degree course but the attribution isn't on the document, I'd copy the whole thing but forum rules prohibit copying, for educational purposes I think this snippet should be acceptably reproduced on educational ground. This is discussing the astrophysical factor (the value that goes into an equation to describe fusion cross-sections) of different fusion reactions.

"
The reaction characteristics R contains essentially all the nuclear
physics of the specific reaction. It takes substantially different values
depending on the nature of the interaction characterizing the reaction. It
is largest for reactions due to strong nuclear interactions; it is smaller by
several orders of magnitude for electromagnetic nuclear interactions; it is
still smaller by as many as 20 orders of magnitude for weak interactions.
For most reactions, the variation of R() is small compared to the strong
variation due to the Gamow factor.
"

I think it is inside older texts I have regarding stellar processes (rather than the texts you'll find on 'fusion energy' and plasma), and I will have to dig them out of a dusty location because it is not a field I am in at all these days. Others here might have better access, but when I studied astronomy (some decades back) it was part of one of the courses. I assumed it was widely understood, or maybe is and you are not aware of this, I'm just not close to this any more. I'll look when I am next where my books are, someone else might have better access to relevant references.

 

[cmb]

and if I am allowed to reproduce this from the same text which I think has some relevance, but delete if it exceeds some sort of rule on the amount of re-quoting allowed;

1.3.3 p–p cycle
Reactions involved in the p–p cycle, the main source of energy in the Sun,
are of fundamental importance in astrophysics. The first two reactions of
the cycle, the pp reaction and the pD reaction have the lowest Gamow
energy G of all fusion reactions, but their cross sections are much smaller
than those of the previous reactions. Indeed, the pp reaction involves a low
probability beta-decay, resulting in a value of S about 25 orders of magnitude smaller than that of the DT reaction. The pD reaction involves an
electromagnetic transition, which is much more probable than pp, but still
much less probable than reactions 1.39–1.43 based on strong interaction.
1.3.4 CNO cycle
Next, Table 1.1 considers the reactions of the CNO cycle, the other main
cycle responsible for energy production and hydrogen burning in stars.
Here the S factors are not very small, but the Gamow energy takes values
close to 40 MeV, thus resulting in cross sections smaller than those of
the p–p cycle at relatively low temperatures. Indeed the p–p chain dominates in the Sun, which has central temperature of 1.3 keV (see Bahcall
et al. 2001). The CNO cycle, instead, prevails over the p–p cycle at
temperatures larger than about 1.5 keV.
1.3.5 CC reactions
Finally, Table 1.1 lists data for the reactions between 12C nuclei. Such
nuclei are the main constituents of some white dwarfs. It is seen that the
S factor is very large, but even at an energy of 100 keV the cross section is
below 10-100 cm2, due to the extremely high Coulomb barrier. We shall
see in Section 1.5.3 that CC reaction

 

[PeterDonis]

I have a chapter from an electronic book

What book?

 

[PeterDonis]

This is discussing the astrophysical factor (the value that goes into an equation to describe fusion cross-sections) of different fusion reactions.

My concern is not the cross sections or equations but the basis for terms like "electromagnetic nuclear interactions", which to me seems like an oxymoron. Any nuclear reaction is going to involve the strong interaction, and given the respective interaction strengths I would expect the strong interaction to dominate the energy change involved. It's been a long time since I studied nuclear physics in college, but I don't recall any classification of nuclear reactions as "mediated by the electromagnetic interaction" or "mediated by the weak interaction" (except for the case of radioactive beta decay, which was typically described as a conversion of one type of quark to another mediated by the weak interaction).

 

[cmb]

What book?

"from a degree course but the attribution isn't on the document", I just said I don't know and I will go looking.

What's your problem here?

I'm explaining these things and saying I'll find it for you, but independent of any referencee, it's frankly flat-out plainly obvious there are 3 distinct types of fusion reaction, independent of any 'book'. It doesn't need someone to actually put their name to it, the physics is obvious;

A) fusion where stuff ends up as kinetically energetic nuclear parts only
B) fusion where only one nuclear part remains and has no energy, but
(i) releases the excess energy as photons, and/or
(ii) releases the excess energy as electrons or positrons, and nutrinos.

The cross-section for all 'A' type reactions are orders of magnitude higher than B(i), which are further orders of magnitude higher than B(ii). Whether you decide that is my own categorisation or not, the physics is a fact.

 

[cmb]

My concern is not the cross sections or equations but the basis for terms like "electromagnetic nuclear interactions", which to me seems like an oxymoron. Any nuclear reaction is going to involve the strong interaction, and given the respective interaction strengths I would expect the strong interaction to dominate the energy change involved. It's been a long time since I studied nuclear physics in college, but I don't recall any classification of nuclear reactions as "mediated by the electromagnetic interaction" or "mediated by the weak interaction" (except for the case of radioactive beta decay, which was typically described as a conversion of one type of quark to another mediated by the weak interaction).

Well, if in the course of a few decades I have fallen into an imprecise and poorly remembered definition of classifications which has diverged from what is accepted now, I stand guilty of a gross misdemeanour and apologise. But give me a chance to find the texts first before passing sentence.

Meanwhile, the physics of the three distinct categories of fusion reactions remains clear, and therefore is not in any way 'a pet theory'. It is physics fact.

 

[PeterDonis]

it's frankly flat-out plainly obvious there are 3 distinct types of fusion reaction, independent of any 'book'. It doesn't need someone to actually put their name to it, the physics is obvious;

A) fusion where stuff ends up as kinetically energetic nuclear parts only
B) fusion where only one nuclear part remains and has no energy, but
(i) releases the excess energy as photons, and/or
(ii) releases the excess energy as electrons or positrons, and nutrinos.

As far as what's left after the reaction and where the kinetic energy ends up, I have no problem with that. But I don't see how any of this maps to terms like "mediated by the electromagnetic interaction" or "mediated by the weak interaction". If those terms are supposed to refer to your B(i) and B(ii), then they don't seem to me to be describing what "mediates" the reaction, but just what carries away the kinetic energy.

 

[PeterDonis]

if in the course of a few decades I have fallen into an imprecise and poorly remembered definition of classifications which has diverged from what is accepted now

I'm not very current in terminology or classification of nuclear reactions, so I don't know what is accepted now. As I have remarked, I don't recall being taught the classification you're describing when I studied nuclear physics in college (which was in the mid 1980s).

 

[cmb]

As far as what's left after the reaction and where the kinetic energy ends up, I have no problem with that. But I don't see how any of this maps to terms like "mediated by the electromagnetic interaction" or "mediated by the weak interaction". If those terms are supposed to refer to your B(i) and B(ii), then they don't seem to me to be describing what "mediates" the reaction, but just what carries away the kinetic energy.

As said, if my descriptions of those three forms of reactions is at odds with someone else's then they can have a problem with it if they really want to make it a problem. But the physics stands so I don't see really what the issue is.

 

[PeterDonis]

the physics stands so I don't see really what the issue is.

The issue before you described the physics in post #93 was that I had no idea what physics the terms you were using referred to. As I said in my response in post #95, I'm not sure the terms "mediated by the electromagnetic interaction" and "mediated by the weak interaction" are very good terms, but the physics you described in post #93 is clear and, as I said in post #95, I have no problem with it.

 

[cmb]

The issue before you described the physics in post #93 was that I had no idea what physics the terms you were using referred to.

That's fine, we can figure out any lack of clarity on terminology no problem, but we understand it's not a pet theory just because I use a different/the wrong terms, right?

Within a nucleus there are still electromagnetic and weak forces, the nature of the fusion result is 'mediated' according to which force within the nucleus does the work on the resultant particles.

It HAS to be an electromagnetic force to create an energetic photon, and as there are no nucleons released then the strong nuclear force does no work on any such energy outputs.

Likewise for weak force.

In answer to your question about a reference for the fission of an intermediate helium 5 from DT fusion, well, if you don't get helium 5 from the 'fusion' of DT, then what does 'fusion' mean? I believe the common view is simply that there is a helium 5 that forms and spontaneously fissions, if you have a different explanation for the formation of helium 4 and a neutron, please provide a reference.

 

[artis]

In answer to your question about a reference for the fission of an intermediate helium 5 from DT fusion, well, if you don't get helium 5 from the 'fusion' of DT, then what does 'fusion' mean? I believe the common view is simply that there is a helium 5 that forms and spontaneously fissions

I think you might be right that indeed in DT fusion for example the free neutron isn't produced before the reaction of D+T is finished and the nucleus of He 5 is assembled which then decays to He 4 + a free neutron.
Wikipedia says the lifetime of He 5 is

The least stable is 5 He, with a half-life of 7.6×10−22 s, although it is possible that 2 He
has an even shorter half-life.

I think the extremely short half life of 5 He is what makes people just disregard it as an intermediary step and write the reaction in it's simple form.

Hopefully @Astronuc or anyone else for that matter can correct this question here , but I do think that not all fusion reaction that are below Fe56 release energy (EM or particle KE) due to the process of the decay of the created daughter nucleus after fusion of two lighter parent ones?
Also it is said that fusion of nuclei lighter than Fe56 is exothermic but if we take the example of DT then the fusion itself is actually endothermic and only becomes exothermic after the daughter nucleus of He 5 undergoes it's fast decay releasing one neutron while the remaining He 4 or Alpha particle gains it's kinetic energy from the original KE's of D and T ?
So in theory if He 5 was stable then D+T would actually consume energy not release energy?

As for fusion on Earth , even if we could catch the gammas the limiting factor is we can't reach the temperatures required for PP or CNO cycle and sustain them in any long term, not to mention the low fusion output for PP for example.
As for particles I think we would actually benefit greatly if DT for example produced no neutrons but just alpha's because our goal is to maximize plasma self heating and the neutron carries away lots of energy while Alpha's would be trapped even in our "thin" plasmas.

 

[cmb]

I think you might be right that indeed in DT fusion for example the free neutron isn't produced before the reaction of D+T is finished and the nucleus of He 5 is assembled which then decays to He 4 + a free neutron.
Wikipedia says the lifetime of He 5 is
I think the extremely short half life of 5 He is what makes people just disregard it as an intermediary step and write the reaction in it's simple form.

Hopefully @Astronuc or anyone else for that matter can correct this question here , but I do think that not all fusion reaction that are below Fe56 release energy (EM or particle KE)

For sure there are a multitude of fusion reactions that are endothermic, in fact probably most of all 'possible' fusion reactions are endothermic.

One which is regularly used is the proton lithium (p,n) reaction which consumes 1.8MeV (or so, I am recalling from memory) and produces a neutron. This endothermic fusion is being used for neutron therapeutics as the neutron source for neutron boron capture therapy, and is also a reaction used in the 'Unicorn' test facility in France (I don't recall the French name) it actually fires lithium ions into the hydrogen gas (rather than protons into lithium) which enhances the directionality of the output neutrons. These reactions aim for collision energies above 2MeV, which provides the energy to excite the resultant fused nucleus into splitting (fissioning) with a neutron output. The neutron is accelerated by the strong nuclear force, the energy for which comes from the excitation state of that fused product.

 

[artis]

One which is regularly used is the proton lithium (p,n) reaction which consumes 1.8MeV (or so, I am recalling from memory) and produces a neutron. This endothermic fusion is being used for neutron therapeutics as the neutron source for neutron boron capture therapy

I do think that for BNCT they use Beryllium as the target due to Beryllium being more chemically stable and safer to work with than Lithium, which among other things burns in contact with water a far as I'm aware.

 

[cmb]

I do think that for BNCT they use Beryllium as the target due to Beryllium being more chemically stable and safer to work with than Lithium, which among other things burns in contact with water a far as I'm aware.

There are different means to create the neutrons for BNCT. Here is a company doing (p,n);
http://www.neutrontherapeutics.com/technology/

Here is the French neutron source;
https://www.researchgate.net/publication/273421998_LICORNE_A_new_and_unique_facility_for_producing_intense_kinematically_focused_neutron_beams_at_the_IPN_Orsay

"LICORNE is a new neutron source recently installed at the tandem accelerator of the Institut de Physique Nucleaire d'Orsay, where a Li7-beam is used to bombard a hydrogen-containing target to produce an intense forward-directed neutron beam."Here is an academic paper;
Appl Radiat Isot
. 2004 Nov;61(5):817-21.
doi: 10.1016/j.apradiso.2004.05.032.

Lithium neutron producing target for BINP accelerator-based neutron source​

B Bayanov 1, V Belov, V Kindyuk, E Oparin, S Taskaev
Affiliations expand

• PMID: 15308150
• DOI: 10.1016/j.apradiso.2004.05.032

Abstract​

Pilot innovative accelerator-based neutron source for neutron capture therapy is under construction now at the Budker Institute of Nuclear Physics, Novosibirsk, Russia. One of the main elements of the facility is lithium target, that produces neutrons via threshold (7)Li(p,n)(7)Be reaction at 25 kW proton beam with energies 1.915 or 2.5 MeV.These are utilising the endothermic neutron producing proton-lithium fusion route.

 

[Alex A]

No reasonable person would call (p,n) fusion.

 

[Astronuc]

I do think that for BNCT they use Beryllium as the target due to Beryllium being more chemically stable and safer to work with than Lithium, which among other things burns in contact with water a far as I'm aware.

⁹Be is used as a target for gamma rays that induce a photon,neutron reaction, since the energy threshold is about the lowest. Be is highly toxic to life forms, so has to used with care. The photoneutron threshold for ⁶Li and ⁷Li is considerably greater.