On 19 February, as planned, the beam stoppers just downstream of the Linac4 ion source were opened, allowing the first H- beam of 2025 to travel into the Linac4 accelerator. This marked the official start of its beam commissioning, which is a meticulous process of carefully guiding the beam through the linear accelerator while fine-tuning all its parameters. To do this, the Linac4 team adjusts the voltages and phases of the high-frequency power waves that travel through the accelerating structures. These waves gradually increase the energy of the H- ions, ensuring that, by the time they reach the end of Linac4, they have been successfully accelerated to an energy of 160 MeV.
As I write, the hardware re-commissioning of the PS Booster (PSB), which began on 13 February, is progressing well and remains on schedule – the injection of the first 2025 proton beam into the PSB is planned for 27 February. From that point onward, Linac4 should be fully operational, providing beams to the PSB in a stable and reliable way, ready for an efficient PSB beam commissioning.
Meanwhile, on 22 February, the hardware re-commissioning of both the Proton Synchrotron (PS) and the Super Proton Synchrotron (SPS) also began. The two accelerators are on track to receive their first proton beams and begin beam commissioning on 5 March and 14 March, respectively.
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From H- ions in Linac4 to protons in the PS Booster When charged particles pass through a magnetic field, their direction of motion depends on their charge. Negatively charged particles, such as the H- ions produced in the Linac4 source, bend in the opposite direction to positively charged particles, such as the protons used in our downstream accelerators. Linac4 accelerates H- ions to 160 MeV before steering them toward the PS Booster (PSB) injection region using magnets. At this point, the H- ions pass through a thin carbon foil, which strips away their two electrons. This process, known as charge exchange injection, leaves behind only protons, which are then guided into the PSB ring using additional magnets. As these protons complete their first orbit inside the PSB, Linac4 continues to deliver fresh H- ions. Since H- ions and protons bend in opposite directions in the same magnetic field, they naturally mix just before reaching the carbon foil. This means that both the protons already circulating in the PSB and the incoming H- ions pass through the foil, where the H- ions lose their electrons and turn into protons, becoming part of the already circulating beam. This process is repeated multiple times until enough protons have been accumulated in the PSB. At this point, the PSB switches off the magnetic fields guiding protons through the foil, ensuring that no extra particles pass through unnecessarily. The accumulated protons are then accelerated and sent further downstream in the accelerator chain. This method of injection allows for efficient multiturn accumulation, leading to higher beam intensities and higher beam densities, which will ultimately provide a large number of collisions in the LHC. |