Швейцарская лаборатория преодолела главное препятствие для строительства будущего коллайдера CERN

A Swiss laboratory has removed what physicists had identified as a potential engineering showstopper for CERN's proposed next-generation particle collider — the inability to produce and capture positrons at the enormous scale the machine will require. On August 24, at the Paul Scherrer Institute (PSI) in Villigen, Switzerland, a proof-of-principle experiment called P³ produced its first positrons using a magnet technology that had never before been deployed inside a working particle accelerator: a 15-tesla solenoid built from high-temperature superconducting (HTS) material. The achievement is a double milestone — validating the positron source concept for the proposed Future Circular Collider (FCC) while simultaneously proving that HTS magnets can survive and perform inside a real accelerator environment. "These are the first positrons for the Future Circular Collider project, so it's an important milestone," said Paolo Craievich, the PSI physicist who co-leads the experiment. That statement carries more weight than most milestone announcements in particle physics: without a high-yield positron source, the FCC's electron-positron first stage — the precision "Higgs factory" that is the scientific heart of the FCC program — cannot reach the luminosity (collision rate) its physics goals demand. P³ was designed from the start to prove that this specific problem is solvable in practice. What Is the P³ Experiment? The PSI Positron Production experiment — P-cubed, or P³ — has been five years in the making, housed at SwissFEL, PSI's X-ray free-electron laser facility in the Swiss canton of Aargau. SwissFEL can deliver an electron beam of up to 6 GeV, precisely matching the energy range FCC requires, making it the ideal host for a test that cannot be run at most facilities in the world. The physics is straightforward; the engineering is not. Electrons from SwissFEL strike a fixed tungsten target. The collision generates a shower of particles — electrons, photons, and, crucially, positrons — flying outward in many directions. The role of the positron source is to capture as many of those positrons as possible and focus them into a tight, usable beam. Historically, a large proportion is lost at this stage because newly produced positrons have extremely high emittance: their paths and energies are widely spread, making it very difficult to gather them into a coherent beam before they escape the capture system. The P³ experiment design addressed this problem directly. "When the electrons hit the target, the positrons are produced traveling in many different directions," explained Riccardo Zennaro, Craievich's co-lead at PSI's Center for Accelerator Science and Technology. "The challenge is to collect as many of them as possible and focus them into a beam. Our initial results suggest that the new system could capture enough positrons to meet the FCC specifications." The Magnet That Changes the Equation At the heart of P³ is a capture solenoid unlike anything previously operated in a particle accelerator. The magnet reaches a field of approximately 15 tesla — more than four times the 3.5-tesla capture solenoid used at SuperKEKB in Japan, currently the world's highest-performing electron-positron collider and the existing state of the art in positron sources. That field difference is not incremental: it is what makes capturing enough positrons physically possible at FCC-ee scale. The SuperKEKB comparison figures come from the P³ experiment's own published design paper. The solenoid is built from rare-earth barium copper oxide (ReBCO), a high-temperature superconducting (HTS) material. Unlike the niobium-titanium (NbTi) and niobium-tin (Nb3Sn) superconductors used throughout most of the world's accelerator infrastructure — both of which require cooling to near absolute zero, approximately 4 Kelvin (−452°F) with liquid helium — ReBCO maintains its superconducting properties at comparatively warmer temperatures, reducing the energy and infrastructure burden of cryogenic cooling. For accelerator operators, this is not merely an efficiency gain: it is a fundamental change in what is architecturally feasible for magnets exposed to the radiation environment near a positron production target. "This is the first time in the world that high-temperature superconducting magnets have been used in a real accelerator," Craievich said. "In the future, the technology is likely to be used in accelerators in functions such as bending magnets." The magnet is built as a stack of "non-insulated" (NI) ReBCO pancake coils — an architecture that improves stability during operation. Surrounding the tungsten target and using its powerful fringe field to bundle the outgoing positron shower, the solenoid works in concert with large-aperture radiofrequency (RF) cavities downstream, which are themselves surrounded by additional superconducting solenoids that further accelerate and contain the beam. The NI HTS solenoid design specifications were published in the journal Superconductor Science and Technology. Why Positron Production Was a Potential Showstopper for FCC-ee Positrons are the antimatter counterpart of electrons — identical in mass, opposite in charge. They were predicted by Paul Dirac's relativistic quantum theory in 1928 and first confirmed experimentally by Carl Anderson in 1932. Producing them in a laboratory requires creating conditions for pair production: a high-energy photon interacting with a heavy nucleus generates an electron-positron pair from pure energy. The physics is well understood; the engineering challenge is capturing and using what emerges. The FCC-ee — the electron-positron first stage of the FCC program — requires positron beam intensities far beyond what any existing source can reliably deliver. The collider is designed to achieve luminosities higher than any electron-positron machine ever built, in order to produce enormous numbers of Higgs bosons, W and Z bosons, and top quarks for precision measurements. Every one of those measurements depends on having enough positrons in the beam. If the positron source cannot meet the specifications, the luminosity targets are unachievable, and the Higgs boson coupling measurements the FCC-ee was built to perform become statistically marginal or impossible. The FCC-ee positron source requirements are detailed in the published feasibility study. Simulations and measurements at P³ suggest the new system could achieve a positron yield roughly four times higher than SuperKEKB's current state-of-the-art, normalized to the drive-beam energy — an improvement that, according to the FCC feasibility study, is necessary to meet the collider's luminosity requirements. The P³ experiment paper provides the full yield analysis. "Our initial results suggest that the new system could capture enough positrons to meet the FCC specifications," Zennaro said. Michael Benedikt, FCC Project Leader at CERN, called the results "an important step for the FCC, validating the proposed approach for the positron source and demonstrating its potential to meet the collider's demanding requirements." In a separate statement, CERN Director-General Mark Thomson added that P³'s results show "the very high positron yield demanded by the FCC injector complex is within reach." Both statements appear in the PSI official press release and Thomson's accompanying LinkedIn post. What Does This Collider Need to Be Built? The Future Circular Collider is the particle physics community's central ambition for the era after the Large Hadron Collider. In May 2026, the CERN Council unanimously endorsed FCC-ee as the top priority of the updated European Strategy for Particle Physics. The machine envisions a 91-kilometer (57-mile) tunnel — more than three times the circumference of the existing LHC — bored at an average depth of 200 meters (656 feet) beneath the Swiss-French border near Geneva. The program is structured in two stages. First would come the FCC-ee: an electron-positron collider operating as a precision Higgs factory, measuring the properties of the Higgs boson and the electroweak sector to unprecedented accuracy. This would be followed decades later by the FCC-hh: a proton-proton collider targeting collision energies around 100 teraelectronvolts — nearly seven times the LHC's current capability — to hunt for particles beyond the Standard Model. The estimated cost for the initial electron-positron stage alone is more than $20 billion, with construction projected to begin in the early 2030s and first collisions possible in the mid-2040s. A final build-or-no-build decision from CERN member governments is expected around 2028. How Does a 15-Tesla Magnet Capture an Antimatter Shower? The physics of positron capture is, at its core, a problem in beam optics. A particle traveling through a magnetic field experiences a force perpendicular to both its velocity and the field direction — the Lorentz force. A solenoid creates a magnetic field along its axis; particles spiraling around that axis are confined by the field rather than lost to the walls of the beam pipe. The capture efficiency scales strongly with field strength. At 3.5 tesla, only a fraction of the positrons emerging from the tungsten target can be redirected into the beam. At 15 tesla — the P³ solenoid's design field — a substantially larger solid angle of the positron shower is captured before it escapes. Downstream RF cavities, also enclosed by multi-tesla superconducting solenoids, then bunch and accelerate the surviving positrons, preparing them for injection into a damping ring where their emittance is further reduced before they enter the main collider complex. The full beam dynamics analysis is documented in the P³ experiment's design paper. The non-insulated ReBCO architecture used in the P³ solenoid is a deliberate engineering choice. In conventional insulated coils, a local quench (a spot where the superconductor loses its zero-resistance state) can propagate catastrophically if not managed rapidly. Non-insulated coils allow current to redistribute circumferentially through direct coil-to-coil contacts, providing an inherent current bypass that makes the magnet more stable in the radiation environment near a positron production target — precisely the environment that previous conventional superconductors could not sustain at high field. Switzerland's Contribution and the Road Ahead P³ is a central element of Switzerland's contribution to FCC development through the Swiss Accelerator Research and Technology (CHART) collaboration — a partnership drawing on PSI's deep expertise in designing, building, and operating accelerator infrastructure. That expertise has a concrete lineage: building SwissFEL required PSI to construct 120 radiofrequency structures for the facility's linear accelerator. The FCC injector would require 440. The experience accumulated at SwissFEL — in RF engineering, precision magnet manufacturing, and cryogenic systems — directly informs what PSI can offer for FCC development. Now that first positrons have been produced, researchers will increase beam intensity and optimize system performance. Collaborators from CERN, IJCLab–Université Paris-Saclay (France), and KEK (Japan) contributed to the achievement — a reminder that the FCC, even at this proof-of-principle stage, is a genuinely international project. Beyond Particle Physics: Medicine and Fusion The HTS magnet technology demonstrated at P³ has already begun propagating into adjacent domains — not as a future possibility but as an active engineering program. In medicine, the same compact high-field solenoid design is under investigation for proton therapy gantry magnets. Gantry systems rotate a proton beam around a patient to deliver radiation precisely to a tumor; current gantries require large conventional magnet assemblies. HTS alternatives would be more compact and more energy-efficient, potentially reducing the cost and physical footprint of proton therapy facilities. This application is confirmed in PSI's own announcement of the P³ milestone. In fusion energy, PSI is collaborating directly with Proxima Fusion — a European company developing quasi-isodynamic stellarator fusion reactors that spun out of the Max Planck Institute for Plasma Physics in 2023 and in July 2026 raised €411 million ($468 million) to advance its technology — on HTS magnet development under the CHART program. Proxima's Stellarator Model Coil demo magnet is targeted for 2027; the PSI magnet team, led by Bernhard Auchmann, had already achieved an 18-tesla HTS solenoid in preparatory work before P³'s operation began. The PSI–Proxima framework agreement was signed in June 2024. The acceleration of HTS magnet applications across these fields is not coincidental. Each successful deployment narrows the gap between laboratory demonstration and industrial manufacturing, building the supply chains and engineering knowledge base that every subsequent application draws on. What Does 'Proof of Principle' Mean — and Why It Matters In the compressed lexicon of particle physics, the P³ result is what the field calls a proof of principle: a first demonstration that a concept works under realistic conditions, not a machine ready for deployment. The full FCC positron injector would dwarf P³ in scale and complexity. But proof-of-principle experiments in this field carry disproportionate weight. The LHC itself was built on decades of incremental demonstrations, each validating one more component of the engineering chain. The Superconducting Super Collider — the United States' proposed 87-kilometer (54-mile) accelerator canceled by Congress in 1993 — demonstrates what happens when funding commitments outrun demonstrated technical readiness. The discipline of validating each component before committing to the full machine is not caution; it is how projects of this scale get built. The first positrons produced at PSI are, in that sense, a small but genuine down payment on one of the most ambitious scientific instruments in human history — and the first concrete evidence that its most difficult remaining engineering problem has a solution. Frequently Asked Questions What is high-temperature superconductivity, and why does it matter for particle accelerators? A superconductor is a material that conducts electricity with zero resistance below a certain critical temperature. Conventional "low-temperature" superconductors like niobium-titanium (used throughout the LHC) must be cooled to approximately 4 Kelvin — around −452°F — using liquid helium, a complex and expensive cryogenic system. High-temperature superconductors, particularly rare-earth barium copper oxide (ReBCO), maintain their properties at warmer temperatures (above 77 Kelvin, or −321°F, in principle), reducing cooling costs and making it feasible to build magnets that achieve fields the older materials cannot sustain. The P³ experiment is the first time an HTS magnet has operated inside a real, working particle accelerator — proving that the technology works under the radiation and beam-loading conditions an accelerator environment imposes. Why are positrons so difficult to produce at the scale a collider like the FCC-ee requires? Positrons are produced by pair production — a high-energy photon interacting with a nucleus generates one electron and one positron. The problem is not generating positrons; it is capturing them. Freshly produced positrons emerge from a tungsten target flying in many different directions with widely spread energies — physicists describe this as high emittance. Existing capture systems (magnetic solenoids around the target) lack the field strength to bundle enough of those particles into a usable beam before they escape. The FCC-ee's luminosity targets — far above any previous electron-positron collider — demand a positron source that captures and delivers roughly four times more positrons per unit of input energy than today's best systems. The P³ experiment is designed to demonstrate that HTS magnets can achieve exactly this. How does the P³ milestone affect the 2028 FCC build-or-no-build decision? CERN member governments will make a final decision on whether to approve FCC construction around 2028. That decision depends partly on whether the FCC's most demanding technical requirements have plausible engineering solutions — and the positron source has been one of the most closely watched open questions. P³'s successful production of first positrons using HTS magnets does not guarantee approval, but it provides the kind of proof-of-principle evidence that feasibility studies depend on. The FCC feasibility study, published in spring 2025, identified the positron source as a key outcome; P³'s results validate the approach the study proposed. Will the HTS magnet technology from P³ appear in other fields beyond particle physics? Yes, and the process is already underway. PSI's HTS magnet program, centered on the same Bernhard Auchmann group that built the P³ solenoid, is simultaneously co-developing magnets for Proxima Fusion's stellarator reactor program and investigating compact HTS gantry magnets for proton therapy cancer treatment. Each application operates at different field strengths and geometric configurations, but all draw on the same fundamental materials knowledge and manufacturing capabilities developed in the accelerator context. The proof at P³ that HTS magnets can survive and perform in a real accelerator environment accelerates confidence in these adjacent applications. ⓒ 2026 TECHTIMES.com All rights reserved. Do not reproduce without permission.