A force field was a piece of technology installed in the anti-matter Pelvanida.
After almost the entire faculty was killed from a bio-bomb, three of the survivors (James Zanasiu, Ender McThair, and Ken) installed the force field so that they could continue living in the facility without requiring chemsuits. However, they miscalculated the amount of time it would take to filter the hazardous gasses out, and so were gone longer than needed.
The force field was the one reason the away team was not instantly killed when they traveled through the Einstein-Rosen bridge. When it became time to leave, Oscar Shelton realized they were going to need the power in the force field to power the bridge. The only problem was that Pelvanida's systems were hard-wired to give complete priority to the force field. To stop the force field from shutting off the bridge's power, four members of the away team (James, Kagetora, Vic, and Seska) stayed behind to prevent the pulses from reaching the motherboard and activating the bridge shutdown. Only Kagetora was succcessful in holding his pulse the entire time. (Card of Ten)