Positron

A positron was a particle. It could be found in anti-matter. (TV: Planet of Evil) Positrons could be produced by particle accelerators and stored in electric and magnetic fields. (TV: The Tsuranga Conundrum)

When a positron came into contact with certain fuel materials, as in an anti-matter drive, heat would be produced, which could then be used to generate thrust. (TV: The Tsuranga Conundrum)

Photons could be produced by the recombination of an electron and a positron. (TV: Time and the Rani) An electron and a positron could also be combined to create orthopositronium. (AUDIO: The Time of the Daleks)

A fixed-atom force field created a shield of positrons which would painfully repel any intruders. (AUDIO: 1001 Nights)