Cleaning up after a helium leak in the world's largest particle accelerator could cost upwards of SFr35 million ($29 million), its operator has warned.

The European Organisation for Nuclear Research (Cern), which built the Large Hadron Collider (LHC), said repairs on the SFr10 billion machine would cost SFr15 million and spare parts another SFr10-20 million.

"We will not be going to our member states asking for more money, we will deal with it within the current Cern budget," spokesman James Gillies said.

Scientists started up the collider with great fanfare in September, firing beams of proton particles around its 27-kilometre underground tunnel.

But nine days later they were forced to shut it down when an electrical fault caused a helium leak.

Gillies said the helium leak caused "quite considerable mechanical damage to the accelerator." Cern expects the machine, buried under the Swiss-French border near Geneva, to be powered up again for tests by June.

"We don't have a precise date for it yet," Gillies added. Cern had originally said the LHC would be restarted in the spring.

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