The box, called "LHC Vlead Tester", will be used to test power converters which supply current to superconducting magnets.
Because superconducting magnets are cooled to cryogenic temperatures there is a device called "current lead" that enables the connection of room-temperature conductors to cryogenic conductors. These current leads are critical devices, therefore the voltage across them is monitored by the power converter which will shut down if a certain voltage threshold is reached.
The Vlead tester just emulates a current lead voltage and with the press of a button, a fault can be triggered.