Electromagnetic pulse

Electromagnetic Pulse, or EMP is the electromagnetic radiation from an explosion (especially a nuclear explosion) or an intensely fluctuating magnetic field caused by Compton-recoil electrons and photoelectrons from photons scattered in the materials of the electronic or explosive device or in a surrounding medium. While organic tissue is unaffected, the resulting electric and magnetic fields may couple with electrical/electronic systems to produce damaging current and voltage surges. The effects are usually not noticeable beyond the blast radius unless the device is nuclear or specifically designed to produce an electromagnetic shockwave. An alternate definition is: a broadband, high-intensity, short-duration burst of electromagnetic energy.

The worst of an electromagnetic pulse generally only lasts for a second, but any unprotected electrical equipment will be affected by the pulse.

Appearances
EMP is mentioned several times in the Halo Universe:


 * In the level Two Betrayals in Halo: Combat Evolved, Cortana diverts John's energy shields into an EMP to disable Halo's Phase Pulse Generators.
 * The detonation of Shiva-class Nuclear Warheads are almost always followed by a massive electromagnetic pulse.
 * The Deep-Space Artifact let out an enormous electromagnetic pulse that briefly canceled out all communications in the Sol System. It later let out another pulse upon deactivation.
 * In Halo: First Strike, John-117 used a Plasma Grenade's EMP charge to disable the electronics of a locked door on Ascendant Justice. This allowed him to open the door.
 * The in-atmosphere jumping of the Prophet of Regret's Assault Carrier to Slipspace above New Mombasa creates a massive electromagnetic pulse that damaged electrical systems in the city, and fried the navigational and safety systems of nearly five dozen SOEIV pods unfortunate enough to drop into the city at that exact moment, plunging them and the Orbital Drop Shock Troopers inside free-falling to certain death.
 * In the aftermath of Operation: UPPERCUT, both SPARTAN-B312 and an unidentified satellite witnessed a purple-tinted cloud emanate from the wreckage of the Long Night of Solace after the improvised slipspace bomb was activated. While this cloud disabled electronics within its vicinity, it is unknown if the cloud itself was an EMP or a sort of pressure wave caused by the sudden disappearance of over half of the ship into slipspace.

Gameplay
EMP is also an in-game effect in the Halo games, that disables energy shields and vehicles. It is produced by certain weapons and equipment.


 * In Halo 2, the Sentinels sometimes emit an EMP when destroyed. This effect disables shields, but vehicles are unaffected.
 * In Halo 3, the Power Drain uses EMP to disable shields, vehicles and other power sources.
 * A charged Plasma Pistol blast will temporarily disable vehicles and energy shields much like the power drain.
 * In Halo: Reach the M319 Individual Grenade Launcher has a secondary function that acts like an EMP. It awards a player an EMP Medal when it kills an enemy, being the only other weapon in the game that awards the medal.
 * In Halo: Reach, Armor Lock can trigger an EMP after use, which can take out a Spartan's shields. Combined with a quick and accurate melee, this can result in an almost instant kill.
 * In Halo Wars, Professor Anders' vehicle, the Gremlin, uses EMP as main armament to disable enemy non-infantry units.
 * In Halo Wars, the Vampire's Stasis Drain Cannon uses EMP as well to drain power from enemy aircraft.

Trivia

 * If you disable a vehicle using an EMP, it will show an animation of some sparks flying around but if you disable it again before it is drivable then the animation will stop and the vehicle will not work.
 * Some vehicles disabled by an EMP will still have full functionality of its weapons if it has any. For example, if a Warthog is disabled by an EMP, the turret will still be able to turn around and shoot.