Division of accelerators, cryogenics and magnetism

The ESS RFQ ("radio frequency quadrupole") is a component of the ESS linear accelerator in Sweden in which radio frequency electric fields are used to focus, group and accelerate a flow of charged particles. The five sections of the ESS RFQ were built in three years by CEA with the companies Mécachrome and AMD, then delivered, assembled in the accelerator tunnel and tested by CEA teams in late 2019.

In order to obtain an operational RFQ, it must be "conditioned". Conditioning is the process of progressively increasing the RF ("Radio Frequency") power in the RFQ to the 730 kW necessary power to reach the nominal accelerator voltage required by the proton beam.

A small amount of power (a few kW) is applied at the beginning of the conditioning process. This power generates electronic activity in the RFQ partly due to contamination of the internal copper surfaces by the ambient air. As the RF power increases, this electronic activity gradually cleans the surfaces. The induced outgassing is then collected by the vacuum system. At the same time, the RFQ cooling system ensures that the RFQ temperature is stable in order to avoid deformations of the cavity that would lead to a change in the RFQ frequency.

The CEA teams, in collaboration with the ESS teams, started the conditioning in June 2021, and on 28 July, the conditioning of the RFQ at the ESS linear accelerator in Sweden was successfully completed. After 7 weeks, the RFQ has been conditioned up to 110% of nominal operating power and has achieved 96% availability in the final stages of stable operation.

Target: 729 kW, 3.2 ms pulse, 14 Hz frequency.
Achieved: 800 kW, 3.2 ms pulse, 14 Hz frequency.

Find the previous highlights on this project here
Contact: Anne-Catherine CHAUVEAU ; Christophe Mayri ; Olivier PIQUET