Linac4 Drift Tube Linac under assembly

After years of design, prototyping and manufacturing, the Linac4 Drift Tube Linac is being assembled at CERN


Linac4 Drift Tube Linac under assembly

One of the Linac4 DTL tanks being assembled at CERN (Image: Maximilien Brice/CERN)

After seven years of design, prototyping and manufacturing, the Linac4 Drift Tube Linac (DTL) is being assembled at CERN, with the first tank undergoing final tests before installation in the Linac4 tunnel.

The Linac4 DTL is designed to take the new linear accelerator's negative hydrogen ions beams from 3 to 50 MeV. It is composed of three tanks containing a total of 108 drift tubes in vacuum. Each tank is a highly complex machine.

Constructing the DTLs has been a considerable challenge for the Linac4 team. “A precision of ±0.1 mm is required when positioning drift tubes in the 7.3 m long vacuum vessels […] and such expertise [is rare],” says Suitbert Ramberger, project engineer for the Linac4 DTL. “We turned to the Los Alamos team responsible for the Spallation Neutron Source DTL, who provided extremely helpful advice on how to proceed.”

 “We wanted to reduce the complexity of the design and make it reliable for 30 years of operation,” says Maurizio Vretenar, project leader of the Linac4 project. “While traditionally DTLs are equipped with screws in order to adjust the drift tube position after the assembly, we concluded that manufacturing techniques had improved to the point where DTLs could be built with fewer means of adjustment. This way we could make do without bellows or double sealing.” 

Some of the most challenging pieces to manufacture were the girders that hold the drift tubes in place. With parts measured in terms of a few tens of microns, the team tested the limits of traditional manufacturing. A new design for supporting drift tubes is pending patent.

The Linac4 DTL team are now a resource to others looking to build drift tube linacs. "The DTL in Bilbao's planned 50 MeV light ion facility of the ESS-Bilbao is an exact replica of the Linac4 DTL," says Vretenar, “as is the mechanical design of the DTL for the European Spallation Source currently under development at the INFN, Legnaro. Both institutes contributed to Linac4's DTL development, and now their teams are following the work of our team very closely." 

"The beauty of the Linac4 DTL design is its puzzle-like simplicity," says Ramberger. "Each complex piece was designed to slot into place for straight-forward assembly... with no extra welding required. It's been a speedy assembly process and soon all the tanks will be ready to go!"