Ports on the Wendelstein 7-X stellarator. (Credit: IPP)

An opening in a vacuum vessel in a thermonuclear fusion research device through which plasma can be monitored, fuel added, impurities removed, or adjustments made within the chamber without compromising the vacuum inside the chamber. Other devices, for example a Thomson scattering laser for plasma temperature measurement or a vacuum pump for impurities extraction, are vacuum tightly connected to the chamber at the port. The ports protrude from the chamber at locations where the presence of magnetic coils or other devices does not prevent this. Facilities that work with deuterium-tritium fusion also use ports for the entry of remotely controlled devices to adjust the chamber interior.