Containment Field

A special forcefield that prevents a highly volatile power source, anti-matter engine core, enslaved magical beastie, an orb of Pure Energy, etc., from obliterating everything around it in a flash of pure white. Maintaining the Containment Field is the most important job of the starship's engineer, the wizard's acolytes, or the Barrier Maiden/Warrior. Inevitably, the Containment Field will begin to weaken, leaking dangerous radiation or reality-warping magic all over the place, and forcing the heroes to drop what they're doing and scramble to restore it (often sacrificing themselves in the process).

Should the heroes fail to restore the field, they may be forced to eject the engine core. Doing so will cripple their ship and leave them defenseless, but it beats certain death by vaporization. In the case of a beastie, it's Final Boss fighting time.

Note that engineers in Real Life prefer to design things with "inherent safety" in mind, so that if something goes wrong they shut down - or at least fail in a controlled way rather than explode spectacularly. For example, modern nuclear reactors are designed with the control rods suspended over rather than under the reactor, so that if power is lost to the electromagnets they all fall into the reactor and stop the fission process, rather than out of the reactor to cause a runaway reaction. Redundant safety systems are also encouraged if a process relies on them for safe operation. This can lead to some examples of Containment Fields (especially sci-fi ones) being a case of Artistic License Engineering but hey, Rule of Cool.

The Containment Field often consists of an energy barrier—similar to Deflector Shields, but on the inside of the ship, and facing inward—though this is not always the case.

A Containment Field is a vital part in many Summoning Rituals.

See Going Critical. Compare Superpower Meltdown.

Anime and Manga

 * In Akira, the cryogenic suspension chamber  acts as a Containment Field, and, naturally, begins to fail towards the end of the movie.
 * Worthless and harmless?.
 * The use of a magnetic field compressing the reactants is how most Gundams are able to fit a fusion reactor (which should, by all rights be the size of a small city) into a mech the size of a small building. As an added bonus, this means if said field fails we get to see Stuff Blowing Up.
 * The 'Mechs and some high-tech vehicles of BattleTech run off of small fusion engines the same way. The game rules assume that they simply shut down when damaged, instead of blowing up dramatically, but that hasn't stopped plenty of players from house-ruling that stuff in anyway, as well as some of the licensed computer games.
 * In the supplementary manga of Magical Girl Lyrical Nanoha, if the characters are training and he's around, Yuuno creates these to minimalize damage to the surrounding area. Of course, since his fields are trying to contain the attacks of some very trigger-happy Persons Of Mass Destruction, these tend to get destroyed.
 * Containment Fields are used in the first two seasons of the cartoon to contain magical beings within an area while keeping out non-magical beings who may be harmed in the battle, with Nanoha's ability to break a barrier as a significant element in second season. As the third season and beyond are set in worlds where even the innocent bystanders are magical beings who would be caught in them, these are rarely used.
 * Unique example in GaoGaiGar. Rather than make a barrier of some kind, the Dividing Driver "shoves" all materials out of its area in circular radius save for the Humongous Mecha and the Monster of the Week.
 * In Hell Teacher Nube, Tamamo's Dangerous Forbidden Technique, Megiddo, unleashes a monstrous blast of destructive magic at its foe. In order to prevent damage to the vicinities (and conveniently focus all its power on the foe,) Tamamo splits his bladed staff into four pieces around the target, generating an egg-like field of annihilation.
 * in RahXephon, Tokyo Jupiter was created by the Mulian forces by erecting a perfectly spherical field (with a swirling surface reminiscent of Jupiter's stormy atmosphere) around Tokyo, sealing it off from the rest of the world. Piercing it is a herculean task requiring tremendous energy expenditures and specialized equipment... or a godlike mecha. Whichever is easier to acquire.

Comic Books

 * Teen Titans, supposedly the only thing Kid Flash can't escape from.

Film

 * The EU technical explanation for how a lightsaber in the Star Wars movies work is that a lightsaber blade is plasma energy suspended within a containment field.
 * When a ghost is captured in the Ghostbusters films, it is then deposited into a laser containment grid. The light is green, the trap is clean.

Literature

 * The magnetic cage/trap in Angels & Demons keeps the antimatter suspended in a vacuum, to prevent it from touching any regular matter and annihilating in a giant kersplosion of pure energy. Of course, some asshole has to go and unplug it. Luckily, it has a battery-backed UPS built-in.
 * The fusion reactors in the Honorverse work by hyper-compressing the reactor plasma in "gravitic bottles." This has the effect that if said containment bottle is lost, even though David Weber is fully aware that a breached fusion reactor stops reacting, the sudden release of pre-existing heat and pressure is more than enough to make a truly scary kaboom.
 * In the Hyperion Cantos, containment fields are EVERYWHERE, and they are powerful. For example, it is noted that while the Hawking Drive is running, containment shields must be up at all times. Should they fail for even a microsecond, especially during acceleration and deceleration, all passengers on board would be compressed into a pile of jelly. Shields range from Class 1s, which can act as a seatbelt, to Class 10s, which deflects all radiation and even nuclear explosions and asteroids.
 * In The Wheel of Time the Dark One has both the seal the Creator established around him, and then it's pierced in the attempt to tap into a new form of magic, and the resultant hole is patched. Making it a containment field on a containment field.
 * The Enchanted Forest Chronicles contains an interesting example:
 * The suspensor field in The History of the Galaxy series is an interesting case. The field doesn't do any containment by itself, as it's too weak to hold anything large. What it does is take any dust particles or grains of sand or anything else small and press them together to form a barrier. Used on spaceships to seal off hull breaches, during digs in desert areas, etc.

Live Action TV
"Grunchlk: You see the green light? That's a biological neutralizer, that is: you could have the Karatonga plague in here, wouldn't touch him. Anywhere else? Pick yer nose and he's dead"
 * The Warp Core on every Star Trek ship is encased in a Containment Field, which fails with depressing regularity.
 * Generally just becomes in danger of failing (often due to very heavy damage), since failure means a Critical Existence Failure unless it is ejected. The same goes for the antimatter storage.
 * And the ejection systems almost never work.
 * There is also the use of force fields which work on a similar principle to the Deflector Shields and are used for everything from emergency containment of hull breaches to security and isolation fields.
 * The Slipstream Core on Andromeda is very similar, but, perhaps, even more volatile.
 * The main fusion reactor of Babylon 5 is maintained by elaborate machinery which acts as a Containment Field.
 * It is never really talked about or in danger of failing. Only once did a homicidal maniac slap a bomb to it big enough to "blow through to the reactor", and in an alternate future that never happened Garibaldi "rigged" the reactor to blow. In 2280, when it is scuttled, the explosion clearly originates from the reactor. The words "Containment" and "Field" are never uttered together in either of those instances.
 * In Stargate SG-1 any Replicator held in a containment field is guaranteed to escape.
 * Given that its main characters are fugitives, Farscape didn't have too many encounters with these. However, in "Die Me Dichotomy," a visit to Diagnosan Tocot's facility reveals that the operating theatre is equipped with a shield that's designed to keep contaminants out of the area, partly for the safety of the patient, but mostly to prevent Tocot from becoming infected while working without his protective mask.

Video Games

 * The final chapter of Half Life 2 is based around this trope.
 * The first part of Episode 1 deals with re-activating a containment field on the Combine's Dark Energy reactor, which is melting down. Surprisingly, reactivating the field does not resolve the situation: the reactor is already too far gone to be salvageable, and is going to explode anyway. The field will just delay the process.
 * In the Crusader games, this trope is often inverted because of No OSHA Compliance. While most of the reactors are shielded, most of the shields seem to be one-way; so the workers can get radiation poisoning but marauding rebels can't just blow 'em up.
 * At the end of Might and Magic 6, you must cast a spell of Dark Containment around the machine you have to blow up. Otherwise you destroy the world, an epic FAIL after about 100 hours gaming.
 * The only time in the Ultima series that the story calls for casting Armageddon, the Avatar first performs the Barrier of Life ritual, to contain and focus the world-shattering power.

Web Comics

 * The Gates in Order of the Stick keep the local god-killing abomination at bay by patching up tears in the fabric of reality, which serves as its prison.
 * Gate? What gate?
 * In Schlock Mercenary, power reactors use gravitic fields to keep neutronium compressed at, well, neutron star density. When the fields fail, or are undone in a wrong way, there's a distinctive SKOOM noise as it nukes its way through the exotic alloy of the a great big hole in the world.
 * Also, small hostile forces can be "tractor-bubbled", as well as other dangerous things, like aggressive nanobots or patients on the way to quarantine. Explosions are contained the same way, but if it's tens of megatons, even a gigantic battleplate's gravitics can't smother it, only redirect wherever it will do less damage.

Web Original

 * Magmatter in Orion's Arm needs to be kept in place by magnetic fields, since the stuff tends to destabilize atomic nuclei. It is a primary structural reinforcement for megascale structures, but it doesn't usually react with matter, instead passing through 99.9% harmlessly. It's very complicated, though a dozen or so pages detailing its behavior can be found on the site.

Western Animation

 * Coop accidentally traps Megas in a containment field in an episode of Megas XLR; he had meant to put up his Deflector Shields, but messed with the settings beforehand.
 * The Real Ghostbusters (and the source movies) has its Ghost Traps and it's Containment Unit, which is just this trope specialized for ghosts. Bad Things happen if you shut off the containment unit. Or if you try to contain something very powerful. Or if Ray sneezes near it. Or...

Real Life

 * Modern particle accelerators are actually capable of concentrating destructive amounts of energy in their beams. A failure of the magnetic fields which steer the beam is a very real eventuality, and accelerator designers implement complex machine protection systems that rapidly react to those events in order to avoid damage to the expensive equipment. Simulations show that one beam from the European LHC, at full power, could punch through forty meters of solid copper. Similarly, the Relativistic Heavy-Ion Collider (or RHIC) at Brookhaven National Lab in New York contains redundant magnetic containment for its high-energy ion beams; it also needs gigantic thicknesses of solid marble and heavy metal (lead, iron etc) to 'catch' the beam safely when it's dumped out of the accelerator ring. Both RHIC and the LHC also employ complex electronic and mechanical systems that essentially act as a mechanical 'containment field', a la Babylon 5
 * Lead and other heavy metals don't work for a beam at the energies the LHC produces. They use a 10-ton rod of graphite and move the beam around so it doesn't melt it.
 * Fusion occurs at such high temperatures that to contain the (generally isotopes of) hydrogen that is undergoing fusion you use a magnetic field to keep that superheated fuel away from the walls of the reactor. Fusion reactors have been built and have been run but the energy required to create, sustain, and contain the reaction has so far been greater than the energy it has been possible to generate.
 * Even smaller devices like fusors found in many colleges, which usually can not produce net energy, require a massive amount of shielding. In these cases, it's less a matter of the released plasma or superheated fuel being an issue, though, as it is a concern about releasing hard X-rays and fast neutrons bouncing around should the lead glass break.
 * However, said magnetic fields not only contain the reaction, they also create the high pressure environment needed for the reaction to occur. Unlike fission, which left to its own will cascade and must be controlled with, yes, control rods, fusion requires a precise environment in term of pressure and temperature. Should the fields fail, then the fusion reaction will simply cease. In other words, if you lose containment, you don't get a boom: the reactor shuts down. Radioactive byproducts of the reaction may still leak out though, depending on how the reactor is engineered.
 * Inertial Containment Fusion uses lasers to initiate and contain a fusion reaction. The largest and most powerful lasers in the world, big as football fields, some of them rated in the Terawatt range, are required. Like Magnetic Containment Fusion, failure of the lasers just causes a failure of the fusion reaction, and the reactor shuts down rather than blow up spectacularly.