The world’s largest cryopump successfully cooled down to nominal temperatures, marking a major achievement for fusion research and the Neutral Beam Test Facility. It has reached its nominal operating temperatures, validating for the first time the integrated operation of the MITICA cryogenic system. This marks an important milestone for fusion research and for the Neutral Beam Test Facility project.
In October 2025, the MITICA Cryopumps, the largest ever built, reached its nominal operating temperatures in Padua, thanks to a close collaboration between the RFX team , F4E and Air Liquide Advanced Technologies (ALAT) . This milestone represents a key step for the Neutral Beam Test Facility and Europe’s contribution to ITER.
The journey began on 16 September 2025, when stakeholders gave the green light to start preparatory activities for the ambitious integrated campaign. Rising the challenge, the RFX Team managed to install the two cryopumps inside MITICA vacuum vessel one month ahead of schedule, creating the crucial time window needed for the October cooldown operations.
The primary goal of the campaign was to bring the MITICA cryopump to nominal operating temperatures: 4.6 K (few degrees above the absolute zero) for the cryopanels and 80 K for the Thermal Radiation Shields, inject Hydrogen gas to test its pumping performances, and conclude with a regeneration phase at 100 K of the charcoal, the pumping material that absorbs the gas as a sponge once cooled down close to absolute zero.
Before starting the cooldown sequence, several technical and administrative tasks were completed first, starting with finalizing maintenance contracts with Air Liquide Advanced Technologies and updating safety procedures. An extensive requalification of pressure release valves was carried out and once reinstalled and tested the MITICA cryogenic system was ready to restart. Maintenance work also took place on the Warm Compression Station and the Oil Removal System, including the replacement of coalescing filters and verification of other key components. The vacuum levels in the cryolines and the two cold boxes of the plant were restored, paving the way for the cooldown sequence finally to begin.
During the cooldown, the team faced several technical challenges. After meticulous investigation, the team composed of RFX personnel supported by F4E colleagues and ALAT technicians successfully solved them. The system finally achieved flawless cooldown: the cryopanels reached 4.6 K, and the thermal radiation shields stabilized at 80 K, validating for the first time the integrated operation of MITICA Cryosystem.
With the first milestone achieved, attention turned to testing the cryopump’s operational performance. Controlled gas injection was performed inside MITICA’s vacuum vessel exploiting the already available Gas, Vacuum & Injection System (GVS), introducing hydrogen at flow rates between 23 and 47 Pa·m³/s over two separate sessions on 27th and 28th of October. The tests provided essential data on the cryopump’s behaviour and its capability to capture and retain gas under realistic operating conditions. The charcoal layer within the cryopump reached full saturation, allowing researchers to study gas release dynamics and system limitations.
Although time constraints prevented the execution of the regeneration test at 100 K, the campaign concluded with a successful warm-up of the MITICA cryogenic system back to room temperature. The data collected are already offering valuable insights into the integrated system’s behaviour and identifying points for optimization in future operations.
The successful cooldown demonstrates the reliability of MITICA’s cryogenic infrastructure and highlights the technical expertise of everyone involved. The successful cooldown and gas injection tests mark a major step forward for the Neutral Beam Test Facility and contribute significantly to ITER’s mission to demonstrate fusion energy as a clean and sustainable power source.
Further tests will be required to fully validate and optimize the integrated MITICA Cryosystem, ensuring its readiness for future operational campaigns. For now, however, we can proudly celebrates this remarkable achievement, a key milestone that confirms the effectiveness of the team work and the strength of the collaboration driving Europe’s contribution to fusion energy.