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.
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.