Full power to the first Linac4 module

Since last week the first of a total of 23 accelerating structures for Linac4 has been undergoing high-power tests. Although still a prototype, this structure is destined to be the first of the 12 PIMS cavities to be installed in the Linac4 tunnel and it has been completely designed, developed and constructed at CERN.


The PIMS prototype.

The new Linac4 has 4 different types of accelerating structures. The PI-Mode Structures (PIMS) are the last stage and are designed to accelerate protons up to 160 MeV. “PIMS have never before been used to accelerate protons”, explains Frank Gerigk, the project engineer responsible for the Linac4 accelerating structures. “In LEP, they were used to accelerate electrons, and now we have modified them and improved several design features to make them suitable for protons”.

The first prototype was entirely manufactured in the CERN workshop. Due to the size of the pieces it was difficult to achieve and preserve the required tolerances during the high-precision turning and milling operations. The final assembly of the pieces was done on the electron-beam welding machine and a long series of tests was needed to develop a suitable welding procedure. "At present a lot of the workshop capacity is being used for Linac4", says Gilles Favre, who coordinates the workshop production. "We are not only working on the PIMS but are also constructing the RFQ, and we are developing prototypes for the other structures and a lot of ancillary equipment used for the cavities".

Last week, the high-power conditioning of the first PIMS module allowed its behaviour to start to be measured under nominal Linac4 operating conditions, that is, 1 MW peak power, pulsed at a repetition frequency of 2 Hz. “So far, the cavity is behaving as expected, which is a big success for the numerous groups at CERN that were involved in the design and construction”, says Frank Gerigk. The tests are the final verification of the design concept before the construction of the other 12 modules, which will start at the beginning of next year and will be carried out in the framework of a collaboration with the Soltan Institute of Nuclear Phyiscs in Swierk (Poland) and the Forschungszentrum Jülich in Germany.

The PIMS module is more than just a prototype, as it will indeed be installed in the Linac4 tunnel. The other modules will be delivered to CERN within the coming two years. Before being installed in their final position, they will undergo high-power tests in the SM18 building, where a dedicated test area is currently under preparation.


by Francesco Poppi