By Mateusz Sosin and Hélène Mainaud Durand (CERN)
The Full Remote Alignment System (FRAS) will be implemented on 68 components of the HL-LHC Project. They will be equipped with a redundant configuration of alignment sensors to continuously determine their position during the different operational phases of the machine. The components will be supported by motorised jacks or motorised platforms to perform their remote adjustment. As this will be a brand-new system, implemented in an accelerator for the first time, a complete strategic plan has been drawn up for its qualification.
The first step is validating its individual constituents; sensors, motor assemblies, and acquisition systems - on dedicated test-setups. The second step is the validation of the full chain of acquisition and control/command on one single component (being a subject of this article), before qualifying FRAS on the Inner Triplet (IT) String test stand, which will consist of 6 HL-LHC components and start operation in 2025.
The Single Component Test (SCT, figure 1) mock-up was deployed at the end of 2023. It is a sophisticated assembly consisting of a full-size magnet equipped with eight Wire Position Sensors (WPS), eight Hydrostatic Levelling Sensors (HLS), three distance measurement sensors and two inclinometers to perform the continuous position determination with the required level of redundancy. It is supported by the integration of three motorised jacks and five motorised adapters and is operated by the necessary infrastructure: acquisition systems and control/command systems. The SCT has played a pivotal role in the validation of FRAS technologies before their deployment, being a rehearsal platform for testing sensors, motorised adapters, alignment algorithms, and data acquisition and control systems. The SCT also supports the collaboration between the BE department’s CEM, GM, and ICS groups, acting as a bridge to validate the interfaces between these teams.
At the end of March 2024, thanks to the SCT, the FRAS team could validate all the installation procedures for the system supports, jacks, adapters, and network routing. Additionally, the prototype electronics and optical modules for Frequency Scanning Interferometry (FSI) and WPS acquisition systems, along with motion control systems, were successfully commissioned and tested. The motorised adapters were also validated, fulfilling the requirement to achieve an installation/dismounting duration of less than five minutes in compliance with the ALARA (As Low As Reasonably Achievable) principle.
During quarters 2 and 3 of 2024, dynamic testing has confirmed the value of the SCT. FSI HLS sensors were subjected to extreme motion conditions to evaluate the impact on the hydraulic network and on the sensors’ reliability during the transitional states, while the FSI interferometer demonstrated a consistent performance under similar conditions. The combined responses of WPS, inclinometers, and longitudinal sensors during motion tests yielded positive outcomes, confirming the micrometric adjustment resolution of motorised jacks.
Beyond hardware testing, the SCT has become an indispensable platform for software and data integration. The Logiciel Général de Compensation (LGC, General Compensation Software) software, developed by BE-GM as a real-time least-square adjustment tool, was deployed and validated with outstanding accuracy in monitoring the radial and vertical positions (~30 μm at 1σ) and roll (~35 μrad at 1σ). The SCT also facilitated the upgrade of FRAS data structures across databases such as InforEAM (the central repository for physical assets at CERN), the Survey database (the source of the theoretical positions, measurements, and computations of all components), and the Layout database (integrating and centralizing information on the whole accelerator complex), bringing them closer to readiness for IT String deployment. Thanks to this successful qualification, the procurement of FRAS equipment for the IT String could be launched.
Looking to the future, the SCT will continue to play a critical role in refining and validating FRAS software and systems. This includes finalising software blocks, enhancing data acquisition capabilities such as achieving one-second intervals for FSI interferometer data, validating complex safety layers, and addressing challenges related to cryostat deformations. The SCT will also serve as a platform for preliminary testing of IT String software ahead of its commissioning in 2025.
Furthermore, it will provide essential training for Work Package 19 (Alignment & Internal Metrology) personnel, ensuring their readiness for FRAS installation and commissioning during LS3.
Related article: validation of FRAS in 2023
Figure 2. FRAS instrumentation installed in the SCT.