First Strike - Cortana 6

Cortana remained calm. After considerable study of the Covenant plasma weapons system, she now understood why they glowed before discharge. The stored plasma was always hot and ready to fire, but the Covenant used an inefficient method to collect and direct the chaotic plasma into a controllable trajectory. They selected the charged plasma atoms with the proper trajec- tory necessary to hit a target and shunted them into a magnetic bubble. The bubble was then discharged; subsequent pulse charges herded the plasma on target.

 For an advanced race, the Covenant's weapons relied on crude brute force calculations and were terribly slow and wasteful.

 She booted the new system she had devised to control the plasma. It used EM pulses a priori to align the stochastic motions of the plasma atoms, herding their trajectories and eleven degrees of electronic freedom into a laser-fine columnated beam within a microsecond.

- Halo: First Strike, Chapter 18