Can we actually harness fusion?

Reflections on fusion history, current events, and predictions for the 'fusion powered future.
Post Reply
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Can we actually harness fusion?

Post by Richard Hull »

Answering the question posed by this post's title can be tricky.

Lets look at how nature does it! (Or, more appropriately, the way we think nature does it).

As is classically imagined and hypothesized, nature does proton-proton fusion in normal stars. There are many classes of stars and we can only guess at more bizarre fusion scenarios. It is of course impossible to really fuse two protons without one of them magically becoming a neutron to form stable deuterium. It is at this point that the imagination of man enters upon the stage. We invision that there are no neutrons on the sun or in stars and that the process is totally protonic in nature. Rather than get into a diatribe over what they think versus what seems more reasonable, the upshot is that energy pours from the sun via fusion processes. This is rather uniformly agreed upon.

Is the sun hot enough to do fusion in its plasma at the surface or in the core? The answer is a resounding, NO! At least not on an efficient basis per unit volume. Most stars are a study of how a fuel supply can be kept on hand to constantly feed a grossly inefficient fusion engine!

All fusion processes, as we invision them are at the mercy of what is termed "nuclear cross sections". These are determined mostly by the type of matter under study and the velocity, kenetic energy, or temperature of same. While these seem diverse quantities, they are really related via the underlying physics of matter.

The cross section is a "make believe" size of the matter particle at a given energy level. The unit of cross section is the BARN = 10e-24cm (derived from being as big as the side of a barn - the early theorists had a sense of humor).

Do not be fooled into thinking that this relates to the real size of the particle at all. It is the mathematically EFFECTIVE size of the particle for calculating fusion and other nuclear reactions. No living being knows what really goes on at this level.

It is hard not to teach a few first principals and look at fusion realistically.

Anyway, The fusion size of hydrogen or its cross section at invisioned solar temperature ranges is extremely small.

There is a second factor in a large body like the sun. This is pressure. Pressure really relates to the number of particles per unit volume at a speciifed temperature. The more particles per unit volume in a give time period and at a given energy the more likelihood there is for fusion at any given cross section. Pressures within the sun are rather easily calculated based on a raft of assumptions which may or may not be correct.

Given the solar volume, assumed mass, assumed temperatures pressures and the cross section of hydrogen, there are pitiably few fusions per cubic kilometer for so much material.

This is good! For if it were higher the sun would not last too long. The pressure and heat energy from the limited fusions over the millions and millions of cubic kilometers of gas in the sun are in a state of balance against the force of gravity trying to compress the gas to hydrogen metal!

Thus, the energy output from the sun is an analog of its total gravitaional potential energy.

This vast outpouring of the self limited fusion process heats our tiny planet.

So, Nature uses gravity to confine quadrillions of tons of hydrogen over a 100,000 mile or larger diameter ball which heats due to this force and ultimately due to increasing temperature and pressure starts a fusion process which grows until the kinetic energy output from the fusion process equals the potential energy of the gravity attempting to compress the gas further. In short, the sun is a mass of unburned nuclear fuel kept on hand and trapped for all time right amidst the burning process!! Neat huh!

From the foregoing it is obvious nature does fusion randomly and poorly per unit volume using gravity to store massive amounts of future fuel within the burning reactor. The process needs no attention and is self perpetuating and self limiting.

What's more, as one form of fuel is consumed it creates higher atomic number matter until all of the original fuel is burned and then proceeds to burn up the higher mass numbers, on and on until we see iron as the end burning stage.

This multi-fuel cycle process of burning hydrogen, deuterium, tritium, helium, lithium, etc all goes on at the same time! That's right, but due to the limit temperatures and pressures, the fusion rates for the other fuels is really slow and grossly inefficient.

Enough of nature's fusion. We just can't do fusion that way. We need a smaller fusion system.

The natural thought is to heat and confine a plasma to pressures and temperatures far beyond the solar inefficiencies to a point where lot so fusions happen per unit volume per unit time.

Not being able to use gravity, we use magnetic confinement of the plasma. The problem is that plasma is conductive and has its own induced magnetic field. Because it is tenuous and flexible, it snakes and resists confinement at extreme energies. More troubles.

Great idea, but the physics of plasmas is such that it appears nearly impossible to do in a reasonable, confinable environment. We are forcing matter to do things that nature never intended. We are, frankly, trying to do exactly what the sun does without the volume and without gravity but at vastly improved effeciency.

This modus operandi is normal for man and some un-natural scenario will ultimately be the winning process for fusion. Nature has a lot of "backdoors".

However, if nature keeps saying no to a specific methodology, how long to we bang our heads against the wall. We are still trying to do what the sun does in miniature.
I think it is time to look for another back door.

Inertial confinement fusion still involves confinement along a pseudo-gravitaional line and heating of bulk matter not in velocity space.

IEC fusion offers an interesting twist. We are not heating bulk mattter or plasmas. We are bringing together, collisionally, in an inertial manner, matter of high cross section that is already at fusion energy!

Nothing to trap, no confinement period, no pressure except that generated by fusion itself.

This may prove to be another unopenable back door but at least it is not more of the same. Our loss mechanism is at least, not classically maxwellian. Whether or not we can convert our losses to recyclable energy to refeed the process is another matter.

Can we actually do fusion?

I think yes. When? Probably when we are able to fund multiple and divergent ideas and paths done "in the small". The old business as usual will result in negative results, as usual.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
guest

Re: Can we actually harness fusion?

Post by guest »

One problem is focus - most fusion prospects rely on a
hot dense area for a long time.I suspect if one can get
a nanu-fusor ( a microscopic sized one ) with small packets of atoms you would have higher chance of fusion because of better focus.
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Can we actually harness fusion?

Post by Richard Hull »

nanostrutured fusion and pulsed packet fusion are a couple of IEC options not heavily investigated up to this point.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Tom Dressel
Posts: 287
Joined: Fri Jun 22, 2001 4:44 pm
Real name:

Re: Can we actually harness fusion?

Post by Tom Dressel »

Richard:

Is proton-proton fusion impossible or just improbable compared to D-D fusion or any of the other fusiom reactions?

Tom
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Can we actually harness fusion?

Post by Richard Hull »

In answer to Tom's question, and quoting the party line.... Yes, proton-proton fusion is invisioned by the current wisdom of particle phsyics. It is rare and tough to do.

It envisions matter creation out of collisional energy and one of the protons becoming a neutron in the fusion process.

It is considered a core level process in the universe.

The embryonic solar mass is invisioned as being a mass of hydrogen gas with only protons and electrons around. NO neutrons. To modern particle physicists neutrons are not formed in stars as separate entities, but as part of the proton-proton fusion chain where one of the protons becomes a neutron.

go to

http:www.historyof the universe.com/fusion.html

Here they show a proton and proton fusing to a deuteron. This is the classic first step as I mentioned above. however, a proton magically became a neutron to balance this , a neutrino and a positron are debris particles.

So, check it out.....Two protons, immutable primary particles, wind up as a neturon and a proton. The neutron is not primary and alone ultimately decays into a proton and an electron and an anti-neutrino. To balance this creational magic, a positron and a neutrino are needed as debris from this fusion to offset the magically created nascent electron and antineutrino locked within the newly formed neutron. It all balances perfectly but makes no common sense whatsoever.

To further delve into how the powers-that-be derived the foregoing magic we are told that the quarks are what is really being balanced here ( A yet deeper mystery still.) Ultimately, flavors, charms, tops and bottoms are brands of quarks, virtual photons and messenger particles of all sorts are said to whiz within this setup as needed to keep the math straight and everything aright.

Sound complicated?.... It is. Sound stupid? You bet, but not to the deeply buried particle physicists who infer hypothesize and calculate more than they observe.

But I digress

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
guest

Re: Can we actually harness fusion?

Post by guest »

I agree with you in principle, Richard. I suspect that it will require one of the "Back doors" to get fusion up and running, and we are still trying to storm the front.

Part of the problem that needs to be resolved is overcoming the electrostatic repulsion of ions. That is a major block. Another problem is to change the effective cross section. That cross section, by the way, is only accurate for ion beams....

A couple blue-sky thoughts on how fusion might eventually play out:

1) The current Tokamaks, IEC's, etc. eventually start working....
2) Perhaps we learn to control Bose-Einstein condensates and use them as fuson targets, or even true "cold-fusion" reactions. They are new science, and eventually will produce major results. They have already been used to bring light to a stop. Of course, call it cold fusion, and you get hung, but it could be called ultra-cold or something like that.
3) Take an atom of H and force the electron temporarily into the proton. Now you have a neutron. Collide it with other atoms to acheive ultra-dense matter and at the same time create the conditions necessary to force the neutrons to decay. There is your ultra-dense, ultra-hot plasma. Any fusion will liberate neutrons, and any neutrons that don't decay will be kicked out by the heat.
4) New physics. Something we don't presently understand may pop up and be used for fusion.
5) We get matter-antimatter working first. Might happen. Then who cares about fusion?
6) Dilithium crystals. Worked for Kirk didn't it?
7) Q. He might get bored soon. He plays a mean trumpet too.
8) Create a giant IEC-like device with a high potential gradient. Get all of the politicians in the world together and blow hot air towards the center. Use candy bars to control power output.
guest

Re: Can we actually harness fusion?

Post by guest »

Clay Codner wrote:
> I agree with you in principle, Richard. I suspect that it will require one of the "Back doors" to get fusion up and running, and we are still trying to storm the front.

5) We get matter-antimatter working first. Might happen. Then who cares about fusion?
There is big money in anti-matter sales if one can figure
a efficent way to produce it. any ideas how? Can it be done at home?

9) Use the free solar fusor
DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 1:13 am
Real name:

Re: Can we actually harness fusion?

Post by DaveC »

Lots of fun trying to imagine the "unimaginable..." or something....

Seriously, if the present fusors are actually doing what it is commonly thought they are... i.e. : producing neutrons as a result of fusing D atoms to He, then the issue is not "doing" fusion since it is being done. The issue is getting the energy out of the fusor and ultimately getting more out than we put in.

Now collecting neutrons in an absorber so that the absorber gets hot.. is at least one very mundane way to extract the energy.... as low temperature heat.

For all on this net, low temperature should be synonymous with "LOW EFFICIENCY ". Recall, Carnot effiency, ....that ultimate thermodynamic limit, which you can't exceed and struggle to even get close to..... is defined as simply: n = (Tmax - T min)/Tmax
where temperatures Tmx and Tmin are in Kelvins.

Using whatever neutron absorber and operating the Fusor below the melting temperature of the container (!!) gives the capability of reasonably good thermal efficiencies. Assuming Tmax for the chamber 1000 C or 1273 K , say 1300K for ease of math, and Tmin is ambient temperature, say 300K , then the Carnot efficiency n = (1300 - 300)/1300 = 1000/1300 = , at 76.9% , not too bad at first glance. But this is just heat. To get work at these temperatures, requires another heat engine, of a more pedestrian sort, which will likely have an efficiency of 25% - 50%. So the overall efficiency is probably around (0.769 *0.5 ) or around 38% max. Since this efficiency would result in either electricity to drive the fusor and/or mechanical work to run the vacuum system, the fusor has to produce about three times the input power, from mass to energy conversions, just to break even. Most conventional power plants have overall thermal efficiencies of about 30 to 40%, but ancillary power requirements are not more than 5% of the power produced. (i.e a 1000 MW plant would require less than 50 MW of power to run the pumps, fans and etc.).

So, as I see it, the challenge is at least two fold:
First is how to scale upwards to produce mass -energy conversions at useful output levels ( one 2 MEV neutron has about 0.32 picojoules of kinetic energy. 1 joule is a watt second or 1/3600 th of a watt hr. ). So, to get 1 w-hr of energy as moving neutrons, you need, 1.125 x 10^16 neutrons. To get 1 watt of energy output, you need 1.125x10^16 neutrons/second.

Thus, we see the basis, once again, for Richard Hull's oft repeated caution about getting too excited about 10^5 neurons per second. We are at the few picowatt levels, and we need watts to megawatts before it gets significant as a power source.

Secondly, to achieve a breakeven condition, and to extract the energy in such a way that fusor shell temps are not excessive, most likely will require a different fusion scheme.

The encouraging part of this is that gravity while effective on all mass, and indifferent to charge polarity, is much much weaker than coulombic forces at anything other than intranuclear distances. This gives the electrostatic method some plausibility as gross containment process. Further electrostatic forces are exerted independently of velocity, meaning that particles do not have to be moving (as in the Tokamaks and other magnetic containment devices) to experience the forces. This is also suggestive of static equilbrium states. But the myriad of other practical issues needed to be solved to even get to the one watt output level, means that IEC methods are as yet, not much farther along than the other methods of doing fusion.

So while these experiments can be done for relatively little money, by the likes of us, we are still in need of more than a few very bright ideas to scale upward.

Dave Cooper
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Can we actually harness fusion?

Post by Richard Hull »

Dave's post is sage advice for the wide eyed among us.

This hard reality has kept the big boys with the tokomaks and mirror machines from so much as turning a 50 cent radio shack toy motor with the billions spent on fusion thus far.

Market realities, engineering problems, etc are all for later, but need to be done and figured on before anyone goes running into the street with the fusion EUREKA!

I will tell a story on the young Bob Hirsch. Once while running a fusor in the cave, they were getting really good numbers never seen before and the elation was there and pleasing to all. As they powered down and killed the HV supply, They noted that the current meters and voltmeters to the fusor did not fall at power off! Instead, they slowly fell with the neutron count which was still there too! After a couple of re-power ups and shut downs repeated the performance, Bob leaped up and said something like; 'we have done it gentlemen... We are near self sustaining action'!!

He ran and called ITT headquarters in New York and the Admiral to announce a landmark event.

While gone, the techs held a conclave and one asked Gene Meeks what the bleeder values were in the shiney, new, giant Universal Voltronics power supply what were and the values of the filter bank. A moments calculation of the RC time constant for the supply and all broke into laughter and ran to stop Bob, but too late........

With egg on his face, he never made that mistake again.

This is told to give everyone a sense of caution and pause when working across multi-disciplinary lines as especially is the case with we "lone-wolf" workers.

Unfortunately, we still boil water or throw it over a cliff to produce all of our "real" energy on this planet and Carot efficiency is important to understand. Woe-betide anyone who thinks they will "end run" this steam engineer's maxim.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Post Reply

Return to “Fusion --- Past, Present, and Future”