A layman's look at fusion tech

[Carlobrand]

Traveller taps the potential of hydrogen fusion to deliver us our magic goodies. Fusion becomes available at TL8 in CT - or TL7 if you're doing High Guard (with the smallest plant being 13.5 cubic meters), or TL9 for Striker vehicles (with the smallest plant being 1 cubic meter irrespective of TL despite the occurrence of fusion power packs for PGMPs/FGMPs at later tech levels), or TL9 in the MegaTraveller universe (with - at TL9 - the smallest plant being 10 cubic meters, and higher tech plants getting much smaller).

For the Scout/Courier, the High Guard power plant produces 500 megawatts output on 2 tons of hydrogen per month - or about 0.77 grams per second.

The sun relies on proton-proton fusion. This is a rather complicated scenario requiring temperatures of 10 to 14 million degrees Kelvin. Two protons collide, one of them immediately spitting out a positron and neutrino and turning into a neutron (the positron pretty much immediately runs smack into an electron and the pair annihilate to throw off a couple of gamma photons); the pair then smack into another proton to form a helium-3 (proton-proton-neutron) and another gamma photon; that helium-3 trio then smacks into another helium-3 trio and throws off a couple of protons (aka hydrogen nuclei) to form a stable helium-4. Total result is 4 hydrogens in, a helium-4, 2 hydrogens, 3 gamma photons and a neutrino out, and the release of 26.73 MeV (as the gammas, neutrino, and increased velocity in the Helium and hydrogens). Note that the neutrino's not worth much except for telling other ships where you are; it carries away about 2% of the energy, so figure 26.22 MeV available energy. To fuse atoms of hydrogen requires overcoming their natural repulsion (they're both positively charged); that takes about 0.1 MeV, so a whole lot more energy ends up getting produced than is spent to do the deed.

http://en.wikipedia.org/wiki/Proton-proton_chain_reaction

Thing is, this process is slow - incredibly slow. One site says 1 in 10^26 collisions in the sun results in a fusion event. The vast majority of proton-proton collisions at the sun's temperature result in a proton pair that just immediately flies apart back into two hydrogen nuclei. To generate 500 million joules each second, we need 1.2 x 10^20 fusion events per second minimum. A mole of hydrogen is one gram, contains 6.02214179×10^23 atoms, and we're burning 0.77 grams per second, so we need roughly one event in 4000; the only table I've found on the subject ...

http://fusedweb.llnl.gov/cpep/chart_pages/3.HowFusionWorks.html

...suggests the best we can manage is a 5-magnitude increase, so that may not be in reach. Might be able to postulate a Traveller P-P design if we speculate that more fuel is being used but the superheated waste plasma's being fed back in repeatedly to give it multiple chances at fusion, with only a trickle of new fuel being added to the mix and a corresponding trickle of exhaust being released to keep the fuel charge in the core at the desired percentage.

An alternate method is deuterium-deuterium fusion. Deuterium is an isotope of hydrogen - a proton with a neutron. D-D fusion is easier; yield is lower, 23.85 MeV per event, but the nuclei are more likely to fuse rather than shove each other away by many orders of magnitude, which is what we want. In fact, it takes us pretty much to the rates we need. However, only about 1 atom out of every 6420 hydrogen atoms is a deuterium (0.0156%).

There's two ways to look at this. If we're filling up on deuterium - or "purifying" to send deuterium to our tanks, then we can have a comfortable fusion reactor in the tens of millions of degrees turning out 500 megawatts on 0.77 grams per second, though only about 0.026% of the fuel's actually getting burned. Why don't we filter out the helium and feed the unused hydrogen back in? Don't know; maybe dumping the used plasma is an important part of dealing with the waste heat.

If we're NOT filling up on deuterium - things get confusing. We can maybe achieve the desired power output at the desired fuel consumption rate by kicking up the temperature an order of magnitude or two - higher rate of deuterium burn compensates for the lower percentage of deuterium in the fuel. The extra effort might explain why drives are more vulnerable to breakdown on unrefined fuel.

However, there's a lot of handwave to that: there just aren't any on-line sources on fusing a tiny percentage of deuterium in a sea of protium (normal hydrogen), so it's speculative whether we can burn deuterium that way and what the resulting output might be. Also, if you can do that, then you can also do that to increase your power output on pure deuterium by an order of magnitude or more. It's hard to imagine a system able to "squeeze" the protium/deuterium mix harder for the desired result without also being able to squeeze deuterium for more power - unless maybe the plant simply can't handle the increased output. Increased output means increased gamma production; that alone could set an upper limit on a given plant's output capacity.

Of course, these numbers assume 100% efficiency at turning the released energy into electricity. Decrease efficiency, increase the number of fusion events per second needed, which means higher temperatures are needed - but that's fine tuning. We don't need that level of detail to understand the basic operating characteristics.

 

[whulorigan]

Thing is, this process is slow - incredibly slow. One site says 1 in 10^26 collisions in the sun results in a fusion event. The vast majority of proton-proton collisions at the sun's temperature result in a proton pair that just immediately flies apart back into two hydrogen nuclei. To generate 500 million joules each second, we need 1.2 x 10^20 fusion events per second minimum. A mole of hydrogen is one gram, contains 6.02214179×10^23 atoms, and we're burning 0.77 grams per second, so we need roughly one event in 4000; the only table I've found on the subject ...

...suggests the best we can manage is a 5-magnitude increase, so that may not be in reach. Might be able to postulate a Traveller P-P design if we speculate that more fuel is being used but the superheated waste plasma's being fed back in repeatedly to give it multiple chances at fusion, with only a trickle of new fuel being added to the mix and a corresponding trickle of exhaust being released to keep the fuel charge in the core at the desired percentage.

One thing to consider:

Traveller presupposes the existence of Nuclear Damper Technology at or above a given TL. Nuclear Damper elements (not weapons-grade, obviously, but spin-off technology) could be part of the design of future Fusion Reactor Cores to increase the reaction rate. In fact it may very well be that it is that particlular technology that puts Proton-Proton Fusion reactions within technological reach in the first place in the Traveller Universe.

 

[samuelvss]

Didn't I see a drink like that in the 7-11?

 

[Carlobrand]

One thing to consider:

Traveller presupposes the existence of Nuclear Damper Technology at or above a given TL. Nuclear Damper elements (not weapons-grade, obviously, but spin-off technology) could be part of the design of future Fusion Reactor Cores to increase the reaction rate. In fact it may very well be that it is that particlular technology that puts Proton-Proton Fusion reactions within technological reach in the first place in the Traveller Universe.

I gotta suspect there's no free lunch there. For a fusion reaction, you're enhancing the strong nuclear force to overcome Coulomb barrier. I suspect the energy you got out of the effort would be equal to or less than the energy you put into the damper to make it happen. That "no free lunch" business seems to be hardwired into the universe's laws.

 

[whulorigan]

I gotta suspect there's no free lunch there. For a fusion reaction, you're enhancing the strong nuclear force to overcome Coulomb barrier. I suspect the energy you got out of the effort would be equal to or less than the energy you put into the damper to make it happen. That "no free lunch" business seems to be hardwired into the universe's laws.

Possibly. But you could just as easily say this of the higher energies necessary to generate stronger EM-Fields to gain higher plasma-densities and temperatures w/o Damper fields.

It is not an issue of a free lunch - the energy going into the reactor is in the energy density of the nuclear fusion fuel. As long as the net energy (minus heat losses) produced is less, there is no free lunch.

You have the same basic issue in an internal combustion engine. The combustion drives the pistons, while at the same time driving the alternator to produce the electricity necessary to ignite the fuel to drive the pistons. The issue is that the energy density of the hydrocarbon fuel is high enough that as long as the fuel is being inputted, the system will continue to run. It is not a free lunch because the hydrocarbon is being used up irreplaceably.

The same is potentially (possibly) true for the Damper-Mediated Proton-Proton Reactor (as long as it is engineered efficiently enough to maximize its potential). If the energy density of the input fuel generates enough output-energy through the nuclear reaction to both power the reactor itself and have a net power surplus (after heat losses), you have a viable reactor.

(I.e. [energy input] = [usable output energy] + [energy to power reactor components] + [heat loss in system] ).

I understand that you might be thinking that you would be putting energy into the strong-nuclear force, only to get it right back out again, but that is not the issue. You only need to add a little to help overcome the coulomb-force, the rest of the energy output (much larger) is the same as for a normal fusion event.

 

[whulorigan]

Muon-catalyzed fusion

Alternatively, Damper-Mediation might be used to help create sustainable Muon-catalyzed fusion.

http://en.wikipedia.org/wiki/Muon-catalyzed_fusion

Temporary Muon-catalyzed fusion has already been achieved in the laboratory over 25 years ago. One of the problems of this approach is that the muons decay, and therefore in order to sustain the reaction a constant new source of muons is necessary. Utilization of damper-technology might aid in creating a "stable" muon environment, thus allowing the muons to continue to catalyze fusion events long term.

 

[mike wightman]

There is an elegance to using the breakthrough in nuclear damper tech to explain the improvement of power plant efficiency at TL12, it's standard for MTU now.

I explain the improvement at TL9 as being due to using artificial gravity to compress the fusion mix with the same force as a star in a very localised volume.

 

[Carlobrand]

I dunno; my knowledge of the physics is layman level - ergo the post title. The damper's supposed to fiddle with the strong nuclear force. Fission and fusion derive their energetic nature from nuclear binding energy - the energy needed to hold the nucleus together. When a large atom fissions, the two products need less binding energy collectively and the unneeded portion expresses itself as released energy; when two small atoms fuse, the resulting nucleus needs less binding energy than the original pair needed, and that expresses itself as released energy (some gamma and increased speed on the part of the nucleus).

I'd thought that binding energy was an expression of the strong nuclear force; i.e. the device creates a field that increases or decreases nuclear binding energy within the nuclei. If so, then adding more binding energy in means you just get that energy back. If I'm not understanding it right, then I'm completely off base with that.

 

[mike wightman]

A nuclear damper can be used to increase or decrease the strong force - it says so

They can be used to make fission reactions more probable by weakening the strong force hence reducing the binding energy, or they can be used to prevent fission by making the strong force stronger i.e. increasing the binding energy.

The same thing in reverse for fusion reactions. Increase the strong force so there is more chance of the nucleons sticking together thus making fusion more likely, or decrease the strong force making fusion less likely.

In the TNE adventure Guilded Lily a ship is prevented powering up its reactor by means of a starport nuclear damper.

 

[whulorigan]

The damper's supposed to fiddle with the strong nuclear force. Fission and fusion derive their energetic nature from nuclear binding energy - the energy needed to hold the nucleus together. When a large atom fissions, the two products need less binding energy collectively and the unneeded portion expresses itself as released energy; when two small atoms fuse, the resulting nucleus needs less binding energy than the original pair needed, and that expresses itself as released energy (some gamma and increased speed on the part of the nucleus).

I'd thought that binding energy was an expression of the strong nuclear force; i.e. the device creates a field that increases or decreases nuclear binding energy within the nuclei. If so, then adding more binding energy in means you just get that energy back. If I'm not understanding it right, then I'm completely off base with that.

Actually, Damper technology as a whole includes manipulation of both the Stong and Weak Nuclear force (Weak Nuclear Force manipulation is the property exploited in Meson Screens, for example).

The Strong Nuclear Force is the force that binds quarks together to form Baryons (such as the Nucleons: Protons & Neutrons) and Mesons. It is about 100 times as strong as the electromagnetic force, but operates only over very short distances (whereas electromagnetism operates to infinite distance via an inverse-square relationship). The Strong Force is "confined" in the sense that as you attempt to separate two or more quarks of unlike charge within a nucleon, the attractive force actually increases drastically, meaning that you cannot directly observe the quarks that make up protons and neutrons.

In the nucleus of an atom (i.e. between nucleons), what you are actually dealing with in terms of nuclear binding energy is residual strong nuclear force, which is mediated between nucleons by the exchange of mesons. The residual force only operates to a disatnce of about 2.5 fm (becuase the mesons have short half-lives and typically have decayed beyond this range). Thus, to get two protons (which have like electric charges and thus repel one another) to be drawn together by the Nuclear force and fuse, one must get the temperature (and thus speed) of the protons high enough so that they manage to get within range of the stronger (and attractive) residual nuclear force.

http://en.wikipedia.org/wiki/Strong_nuclear_force
http://en.wikipedia.org/wiki/Nuclear_force

Your understanding of binding energy is essentially correct, but the issue has to do with how I am suggesting we implement the technology.

For a Damper-Mediated Proton-Proton Reactor (DM-PPR), I am suggesting that the protium plasma be magnetically constricted to subcritical density/pressure/temperature in an injector apparatus. Inject this sub-critical plasma through the center of a "toroidal" Nuclear Damper ring-apparatus that uses one (or both) of the two following approaches:

1) The Strong Nuclear Damper increases the Nuclear force just enough to "help" the protons over the coulomb barrier and then let the native Residual Nuclear Force of the protons take over after it has passed beyond the torus into the reaction chamber proper. You are only adding a little Nuclear Force, much less than what is released in the reaction. An analogy can be made to dynamite, for example. You add a little bit of fire/heat to detonate the dynamite (i.e. to push it over the ignition temperature), which releases a lot more heat/energy in an explosion as a result.

2) Use a Damper-Field that manipulates the Weak Nuclear Force to stabilize the mesons that mediate the Residual Strong Force so that the mesons have a greater half-life (and thus greater range), thus allowing the protons to "feel" the Residual Strong Force at a greater range, requiring less thermal energy/pressure to initiate a fusion reaction as a result.

​

 

[whulorigan]

Tauon-catalyzed fusion

Also, concerning Muon-catalyzed fusion that I mentioned upthread:

One could employ the exact same approach using Tauons (super-heavy electrons) instead of Muons, which are almost 3500 times the mass of the electron (and thus would draw nuclei closer than even Muons, which are only a little over 200 times the electron mass).

Perhaps the Tauon approach would be necessary to achieve Proton-Proton Fusion. Such tauons are actually almost twice as massive as protons, so they actually may form an exotic atom with the tauon in the center and the proton orbiting about in a "proton cloud", that would form a diatomic covalent "proton-bond" with other similar exotic atoms.

 

[Carlobrand]

...Your understanding of binding energy is essentially correct, but the issue has to do with how I am suggesting we implement the technology.

For a Damper-Mediated Proton-Proton Reactor (DM-PPR), I am suggesting that the protium plasma be magnetically constricted to subcritical density/pressure/temperature in an injector apparatus. Inject this sub-critical plasma through the center of a "toroidal" Nuclear Damper ring-apparatus that uses one (or both) of the two following approaches:

1) The Strong Nuclear Damper increases the Nuclear force just enough to "help" the protons over the coulomb barrier and then let the native Residual Nuclear Force of the protons take over after it has passed beyond the torus into the reaction chamber proper. You are only adding a little Nuclear Force, much less than what is released in the reaction. An analogy can be made to dynamite, for example. You add a little bit of fire/heat to detonate the dynamite (i.e. to push it over the ignition temperature), which releases a lot more heat/energy in an explosion as a result.

2) Use a Damper-Field that manipulates the Weak Nuclear Force to stabilize the mesons that mediate the Residual Strong Force so that the mesons have a greater half-life (and thus greater range), thus allowing the protons to "feel" the Residual Strong Force at a greater range, requiring less thermal energy/pressure to initiate a fusion reaction as a result.

​

So, you add energy to get back energy, but because many more reactions are occurring than would otherwise occur, you get more energy for your investment than what you put in.

 

[mike wightman]

That's why nuclear dampers are Traveller magic tech

TL12 is a very long way off - unless we run into a TL11 culture with TL12 secrets hidden away in their databases...

In a way it almost like being able to control nuclear reactions rates the way we can control chemical reaction rates now.

Handwave room temperature superconductors, sub-atomic particle spin manipulation and Higgs field interaction and you'll get away with it

Anyway, Traveller technological breakthroughs allow for grav field manipulation of the fusion plasma and nuclear damper catalysis.

 

[whulorigan]

So, you add energy to get back energy, but because many more reactions are occurring than would otherwise occur, you get more energy for your investment than what you put in.

You add energy to get the reaction started. The energy you are releasing is already stored in the Hydrogen Fuel as potential energy, just as the energy in an exothermic chemical reaction is already stored as chemical potential energy in the chemical reactants.

You have to remember that the potential energy stored in the hydrogen fuel is greater than the energy consumed by the power plant (including the dampers) and the useable output energy produced (the difference is lost to the system as waste heat/increased entropy overall). Otherwise, you do not have a self-sustaining reactor dependent only upon fuel-input.

Energy Conservation is not being violated. The key is in the engineering design details.

 

[SanDragon]

http://traveller.mu.org/house/fusion.html

I CNO fusion!

 

[whulorigan]

http://traveller.mu.org/house/fusion.html

I CNO fusion!

CNO Fusion tends to dominate in stellar cores above 1.3 Solar Masses, becuase it requires higher ignition temperatures.

Proton-Proton reactions begin at around 4.0-5.0 x 10⁶ K, whereas CNO begins around 15.0 x10⁶ K.

http://en.wikipedia.org/wiki/CNO_cycle

While the CNO Cycle would be useful in higher TL power plants due to its higher energy output potential, the technical ability to initiate the p-p chain would need to be achieved first before one could hope to achieve CNO-level energies.

But it is an interesting thought for higher TL power-plants.

 

[whulorigan]

Fusor (IEC - Inertial Electrostatic/Electrodynamic Fusion)

Also, just to throw it out there for consideration sake, the Fusor (Inertial Electrostatic/Electrodynamic Fusion - IEC) is a commercially available Fusion Reactor (caveat: NOT a Power Plant - it is externally powered) that is used in industry as a Neutron Source.

http://en.wikipedia.org/wiki/Fusor
http://www.nsd-fusion.com/

They can be cheaply built for between $500 and $3000, and in fact have been built by high school students for science fairs. There are one or two companies that produce them commercially. (Plus they look really cool).

They are currently not considered viable as a power source (not producing enough energy to self-power the reactor and produce surplus power), but with the application of some of Traveller's other technologies to the problem, perhaps that will change.

Also, just for fun (designed by Robert Bussard):
http://www.ibiblio.org/lunar/school/InterStellar/Explorer_Class/Bussard_Fusion_systems.HTML

 

[HG_B]

IMTU advances in applied quantum physics has enabled the manufacture of P-P fusion plants by inducing quantum tunneling. This basically means "cold fusion".

The seemingly excessive use of H2 is because most of it is used as a coolant. The plants use alpha, beta & gamma voltaics. In addition to capturing the neutrons to create/harness the indirect ionizing radiation which is converted. Lastly, thermocouples with the L-hyd on the "cold side" wring out the last bit of useable energy. In short, they use everything except the squeal to produce power. Almost no moving parts.

n.b. If you have an external coolant source while planet side your fuel lasts a VERY long time.

 

[whulorigan]

IMTU advances in applied quantum physics has enabled the manufacture of P-P fusion plants by inducing quantum tunneling. This basically means "cold fusion".

Not a bad idea.

The seemingly excessive use of H₂ is because most of it is used as a coolant.

Could the H₂-coolant be recycled closed-cycle (utilizing hull radiators), or is it vented or utilized in a chemical-cryogenic process for cooling?

The plants use alpha, beta & gamma voltaics. In addition to capturing the neutrons to create/harness the indirect ionizing radiation which is converted.

For others reading this thread:
Radioisotope Generators: http://en.wikipedia.org/wiki/Atomic_battery

The Gamma Voltaics and Neutron-capture are fine ideas to wring additional power from the reaction, but I would suggest that the output high-energy plasma stream of alpha & beta particles from the reactor might produce more power directly from the magnetic fields generated by the high-energy moving charged particles.

 

[HG_B]

Could the H₂-coolant be recycled closed-cycle (utilizing hull radiators), or is it vented or utilized in a chemical-cryogenic process for cooling?

It could be closed loop but, that would require massive radiators and, would not be in keeping with the amount of PP fuel used in the rules. I did it this way to account for fuel usage rules. Plus, the cooling use (expelling the heated H₂) allows for thermocouples is a more realistic way.

The Gamma Voltaics and Neutron-capture are fine ideas to wring additional power from the reaction, but I would suggest that the output high-energy plasma stream of alpha & beta particles from the reactor might produce more power directly from the magnetic fields generated by the high-energy moving charged particles.

That could work as well I think. Just depends on how efficient the voltaics become. Maybe, TL 9-11 use the Plasma stream while 12-15 use voltaics. Could be a nice bit of fluff to differentiate PP's at various TL's.