Release the beams! - Linac4 ready to hit the 50 MeV mark

The Linac4 accelerator is now prepared to reach 50 MeV. This milestone energy - expected in the coming weeks - will allow the machine to act as a replacement for the ageing Linac2, four years before it takes over at the head of the accelerator chain in 2020.

Inside the Linac4 tunnel, the final DTL cavities will guide beams to 50 MeV. (Image: Stephan Russenschuck.)

The Linac4 accelerator will bring H- ion beams (hydrogen atoms with an extra electron) up to 160 MeV for injection into the PS Booster. As a key part of the LHC injector upgrade programme, Linac4 will allow the PS Booster to double its beam brightness, which will contribute to increasing the LHC’s luminosity.

Linac4 will soon bring beams up to 50 MeV - the current energy delivered by the Linac2 accelerator. This milestone follows on from another recent accomplishment: the installation and commissioning of the final Drift Tube Linac (DTL) tank. Using an innovative (and patented!) design, three DTL tanks, now fully commissioned, will take the beam from 3 MeV to 50 MeV. “This achievement was eight years in the making,” says Maurizio Vretenar, the Linac4 project leader. “We saw these tanks through from the drawing board to the test bench, and now to the accelerator chain itself; we couldn’t be happier with their performance so far.”

Once the DTL tanks were completed in the workshops, getting them into Linac4 wasn’t just a matter of plug-and-play. “When we speak about commissioning and installation, there’s a lot more to it than just moving the tanks into the tunnel,” says Suitbert Ramberger, project engineer for the Linac4 DTL. “We had to connect the waveguides, check if the water cooling system was working, connect the radio frequency (RF) probes, perform RF ‘cleaning’ to ensure the integrity of the vacuum - it was a long checklist.”

Ensuring faultless connections between the disparate accelerator components was a key part of the commissioning process. The DTL cavities were aligned with ±0.1 mm precision to each other and to the rest of the Linac4 line, including the preceding Radio Frequency Quadrupole (RFQ) and beam chopper, which take the beam from 45 keV to 3 MeV.

“The first step will be to accelerate the beam through the first tank of the DTL, to find the correct settings of the low energy part,” says Alessandra Lombardi, who is in charge of the commissioning phase of Linac4. We will then accelerate progressively through the second and the third tank to the energy of 50 MeV.”

As soon as the beam has been fully commissioned up to 50 MeV, the Linac4 team will move on to the next item on the schedule: the Cell-Coupled DTLs (CCDTL). The remaining cavities are set to be installed and commissioned by the end of 2015, bringing Linac4 up to a staggering 100 MeV.

Read about Linac4's commissioning with 12 MeV beams in: “First beam in Linac4 DTL”.

The Linac4 design

Linac4 accelerator is home to 4 types of RF structures: the Radio Frequency Quadrupole (RFQ), accelerating the beam from 45 keV to 3 MeV; the Drift Tube Linacs (DTL), from 3 MeV to 50 MeV; the Cell-Coupled DTLs (CCDTL), from 50 MeV to 100 MeV; and, finally, PI-Mode Structures (PIMS), taking it up to 160 MeV.

by Katarina Anthony