Fission of a nucleus of U-235 produces ~205 MeV (less than 1 MeV per nucleon). Fusion of a deuteron (H-2 nucleus) and triton (H-3 nucleus) produces 17.6 MeV or about 3.52 MeV per nucleon. One of the most energetic fusion reactions, D + Li-6 -> He 4, releases 22.4 MeV (per reaction), but that is only 2.8 MeV per nucleon.
In fission and fusion, the much of the energy released in the reaction is transformed into kinetic energy of the products - which means high temperature. This 'thermal' energy can then be transformed by a machine, e.g. turbine into mechanical energy to drive an electrical generator, which in turn produces a variable magnetic field, which in turn produces 'electricity'. The process thermal to mechanical energy conversion, usually involving the Rankine steam cycle, is quite inefficient. A Brayton cycle might achieve slightly higher efficiency depending upon the temperature difference between hot reservoir and cold reservoir.
Anyway, as for anti-matter, to create an antiproton, one needs to input an energy of at least 938.272 MeV, the rest mass of a proton/anti-proton, so that is 938.272 MeV per nucleon. Now the creation of an anti-particle must observe certain conservation laws, so by the typical method of anti-proton production (viz proton-proton collision), a proton is also created, so the initial colliding pair of protons must have in input of kinetic energy of at least 1.876 GeV or still 938.3 MeV/proton. However, collisions of protons are very difficult, and they rarely line up just right for a head on collision, and most of the time, the protons just scatter without a reaction, so one has to put more energy into the colliding protons to increase the probability that a glancing collision will exceed the threshold for the reaction which produces a proton/anti-proton pair. IIRC, one typically inputs 4-6 GeV per colliding pair of protons, and even then if one would get one anti-proton for 1000 proton-proton collisions, that is 4-6 TeV spent for one anti-proton. Then one can calulate how much energy it would take to create a gram of anti-protons. (Don't forget the positron production)
Fusion suffers from a similar problem in that the nuclei must have sufficient kinetic energy to overcome the Coulombic repulsion, and even then the nuclei are more likely to scatter than react. The kinetic energy, usually several keV to 200 keV means high temperature (1 ev = 11605 K, or 1 keV = 11605000 K), which means the atoms (light atoms) are ionized. A consequence of the ionization means that the electrons are also heated, and when the plasma is isolated/confined by a magnetic field, the electrons radiate a lot of energy as cyclotron and brehmsstrahlung radiation. Another consequence of the high temperature is high pressure, which is a function of particle density and temperature. Since there are practical limits on magnetic field strength and material strength (limits on human technology), there are practical limits on plasma densities (e.g. ~1014 particles/cc as compared to a typical gas at STP, ~1019 atoms or molecules/cc, and solids ~1022 atoms/cc) which we can create on earth. Stars are not so encumbered.
In a star, the intense EM fields, well beyond what we create on earth, with the possible exception of the few microseconds following the initiation of a fission (nuclear) or fusion (thermonuclear) bomb, can create very high energies in the multi-GeV range, and so anti-matter production is possible, but the anti-protons would not survive very long. High energy protons in the solar wind or galactic cosmic radiation cause the prodcution of antiparticles in the upper atmosphere. That is the source of pions and muons (pion decay) that scientists like Wilson detected back in the early 1900's.
Bottom line - anti-matter is difficult and very expensive for humans to produce.
