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ITER plasmas may undergo a violent termination known as a disruption if the plasma becomes unstable. A system will be employed on ITER to rapidly dissipate the plasma energy during a disruption event in order to minimize JxB forces and thermal impulse damage to the plasma facing components. The disruption mitigation system, which is not yet designed, will likely use gas jets or solid pellets to inject a large quantity of gas into the plasma in a few milliseconds. An amount of gas on the order of 1025 atoms will be needed to prevent runaway electron formation during the disruption that could result in holes being formed in vacuum vessel components. A neutral particle load of this size will increase the vacuum vessel pressure significantly if the pumping system is unable to respond during the relatively short duration of the gas injection. The amount and type of gas to be employed and its expected effect on the ITER vacuum system cryopumps, forepumps, and neutral beam injectors will be presented. |