RF conditioning of the ESS Drift Tube Linac under way

RF conditioning is in progress in the ESS Normal Conducting Linac. Image: Ulrika Hammarlund/ESS

RF conditioning of the ESS Drift Tube Linac (DTL) has started in the Normal Conducting Linac (NCL). This is an important step towards the next phase of beam commissioning, which will involve sending the proton beam through the first 40 metres of the ESS Accelerator.


Drift Tube Linac 2,3 and 4 in the ESS Linac.

Francesco Grespan/INFN

RF conditioning is the process of feeding cavities with slowly increasing radio-frequency (RF) power, until the nominal accelerating field gradient is reached and is sufficiently stable for beam acceleration. For the DTL cavities, the requirement is 3 MV/m at 14 Hz and 3.2 ms. Last week saw the first RF pulses sent to DTL tanks 2, 3 and 4, after several months of installation and testing as well as to tank 1 that was already tested with beam in 2022.

The now ongoing RF conditioning of DTL tanks is a crucial step in making the NCL ready for beam and will continue until April. The routine for conditioning, which also includes testing of all safety functions, the vacuum, water-cooling  and RF systems, as well as the control systems and software, was developed and tested when DTL1 was conditioned last year and will continue to be optimised in the coming weeks. 


All conditioning activities are supervised and controlled from the ESS main control room. A small celebration was held last week to mark the start of DTL RF conditioning.

Benjamin Bolling/ESS

Beam commissioning – where the proton beam is to be sent from the Ion Source up to a shielded collection vessel, a so-called Faraday Cup, placed after DTL4 - is expected to start in April and be completed this summer.


In the Klystron Gallery: RF power is produced by klystrons and fed to the accelerator cavities via waveguides.

Ulrika Hammarlund/ESS

The fifth and last DTL tank will be installed after the summer, and will be tested with beam together with the superconducting linac.

DTL inside

DTL tanks are coated with copper on all internal surfaces for good electrical conductivity.

Ulrika Hammarlund/ESS

The Drift Tube Linac is an in-kind contribution from Italian partner INFN (National Institute of Nuclear Physics). It consists of five tanks designed to accelerate the proton beam from 3.6 to 90 MeV. INFN designed and built the ESS DTL, assembled and tuned it in a designated workshop on the ESS site and are also an integral part of the installation, testing and commissioning activities, together with the ESS Linac Group and other key teams in the Accelerator Division, as well as the Operations team and numerous support functions across ESS.


Screenshot from the Public Operations Screen and an Operator Level OPI showing the RF power/field gradient in DTL tanks 1, 2, 3 and 4.

Accelerator schematic

A schematic drawing of the 600-metre-long Linear Accelerator. The area highlighted in blue is the superconducting part where the cryomodules are installed.