Dilithium crystals when exposed to a magnetic field change the quantum state of antimatter so it can co-exist with matter as matter/antimatter molecules . First the crystals are exposed to a high frequency electromagnetic field. Then the antimatter stream is passed through the crystals and pick up energy from the crystal that changes the quantum state. A flow of normal matter with the same mass flows below the crystals as the antimatter passes through the crystals into the matter stream they form molecules made of matter and antimatter called warp plasma. This is stored in the warp core and used in the warp coils and power cells.On at least one story line there was an imbalance in the fuel mixture this is a kind of warp chemistry started in our time. Warp Plasma does not have to be one kind of matter/antimatter molecule.
The reason I think this is correct is because on the star trek web site it shows this and in one of the shows dilithium crystals deposits on a planet had a formation where the crystals where resonating from geological heat. This was producing quantum vibrations that where destroying the planet. Also dipositronium is made by firing a beam of positrons at ordinary silica and it picks up energy from the reaction and produces the “ortho” state needed to form dipositronium a form of warp matter we can make today.