Commissioning of the first HElmholtz LInear ACcelerators (HELIAC) cryomodule with heavy ion beam


The HElmholtz LInear ACcelerator HELIAC is a continuous-wave linear accelerator at GSI/FAIR that opens up new research opportunities with its continuous particle beam. The first superconducting module for HELIAC has been developed, assembled and tested at the Helmholtz Institute Mainz (HIM) in the past years. Following transport to the GSI/FAIR campus, it has now been successfully commissioned with a beam of helium and argon ions. In further tests, the electrical field strengths required to accelerate the heavy ion beam were significantly exceeded.

The module consists of in total four superconducting radio-frequency cavities and two high-field solenoid lenses, which are also superconducting. For the assembly, the accelerator cavities had to be combined into a complete so-called “accelerator string” in the almost complete absence of interfering particles. For this purpose, the HIM clean room with ISO class 4 (similar to the rooms in use for computer chip production) and a special production line for the insertion and extraction process was used. Afterwards this string was assembled into a complete cryomodule.

In the summer of 2023, the fully equipped module, which weights almost eight tons, was transported from Mainz to Darmstadt to the GSI/FAIR using a special truck. The assembly and integration of the cryomodule followed, as well as the connection to the local cryogenic liquid helium supply. After a successful cool-down procedure, the individual superconducting acceleration cavities were able to go into operation with the newly installed radio-frequency power supply.

In December 2023, the time had come: After five years of development, construction and commissioning, the helium beam from the GSI high charge injector was accelerated for the first time in the HELIAC-Kryomodul 1, recently with argon beam an energy of approx. 13.5 million electron volts in a stable manner and with good beam transmission has been reached. The acceleration gradients required to accelerate heavy ions are up to three times higher and are also available. Furthermore it has been shown that it is possible to vary the beam energy over a wider range with this cryomodule without losing particles. This is a considerable advantage of the particle-dynamics concept developed at the Goethe Universität Frankfurt, which is being applied in practice for the first time here.

The proposed HELIAC, in which up to four such modules are to be used, will in the future accelerate heavy ion beams to up to 10% of the speed of light. The energy required for particle acceleration will be reduced by up to 90% compared to conventional accelerators through the use of superconductivity. The newly developed cryomodules make a significant contribution to saving energy and thus to reducing CO2 emissions.

Once the HELIAC project is approved, funded and implemented, the fully assembled and tested modules will then be available to the scientists to carry out experiments in nuclear and atomic physics, nuclear chemistry and in the materials sciences with continuous wave heavy ion beams of the highest intensity.

The staff of the GSI Linear Accelerator Department and the ACID 1 section of the HIM have in particular contributed to this success, as well as further specialist departments of GSI/FAIR.

The prototype phase of the HELIAC project, reported here, is financially supported and funded by the Helmholtz Association of German Research Centers (HGF), the Federal Ministry of Education and Research (BMBF) and the European Union (European Regional Development Fund). (CP)