The Large Hadron Collider (LHC) near Geneva will be out of action until the spring while engineers investigate a fault, it was announced.
A large amount of helium leaked into the tunnel on Friday, forcing the £3.6 billion particle accelerator to be shut down, less than 10 days after the start of the project which scientists hope will unravel the secrets of the first moments of the universe.
The European Organisation for Nuclear Research (Cern), which is running the experiment, said an initial investigation suggested a faulty electrical connection between two of the accelerator's magnets could be to blame.
The collider requires temperatures just above absolute zero (-273.15 degrees C) to allow particles to be steered around the circuit.
But as a result of the fault, the temperature of the magnets rose by about 100C.
The affected area of the 27km (16.8 mile) tunnel must be brought up to room temperature to allow engineers to inspect the magnets, and this process will take three or four weeks.
Robert Aymar, director general of Cern, said: "Coming immediately after the very successful start of LHC operation on September 10, this is undoubtedly a psychological blow.
"Nevertheless, the success of the LHC's first operation with beam is testimony to years of painstaking preparation and the skill of the teams involved in building and running Cern's accelerator complex.
"I have no doubt that we will overcome this setback with the same degree of rigour and application."
Cern said the time needed to repair the fault meant there was no chance the accelerator would start up again before the scheduled winter maintenance period, meaning the LHC would not be activated until spring 2009.