Antimatter annihilates as soon as it touches ordinary matter, which makes storing and moving it one of the hardest engineering problems in physics. CERN’s BASE collaboration has now demonstrated a practical way forward with a new transportable trap system called BASE-STEP.
A portable Penning trap for antiprotons
BASE-STEP (Symmetry Tests in Experiments with Portable Antiprotons) is a fully functional, transportable Penning trap designed to carry antiprotons from CERN’s Antimatter Decelerator hall to quieter labs with more stable magnetic fields.
The apparatus is mounted on an aluminium frame about 2.00 × 0.87 × 1.85 m in size and under 1,000 kg, so it can be moved with standard forklifts and cranes and fits through normal doors and corridors.
At its core are two electrode stacks inside a cryogenic vacuum chamber, sitting in the bore of a superconducting magnet:
- Catching Trap (CT) – receives antiprotons from ELENA, slows them with a degrader foil, and captures them using high‑voltage pulses. Rotatable elements let the team switch between injection, isolated storage and ejection modes, effectively acting as an “airlock” for the ultra‑high vacuum.
- Storage Trap (ST) – provides up to three months of storage at pressures below 10⁻¹⁶ mbar in the trap centre.
The electrodes are made from gold‑plated oxygen‑free copper, separated by precisely machined sapphire rings to ensure excellent thermal conductivity and low energy loss. Non‑destructive axial and cyclotron detectors with superconducting toroidal coils monitor the particles’ motional frequencies without disturbing them.
Keeping a cold magnet stable on a truck
Unlike conventional systems that are transported warm and unpowered, the BASE-STEP superconducting magnet remains cold and operating during transport. The support structure, verified with Finite Element Method simulations, can withstand accelerations of up to 2 g in any direction without exceeding material stress limits.
Maintaining ultra‑high vacuum while moving is equally critical. A differential pumping system connects the cryogenic trap chamber to an inlet region at room temperature, where the residual gas pressure is kept below 10⁻¹⁰ mbar. An inlet valve and two rotatable trap electrodes can close off the pumping channel and further block residual gases, protecting the stored antiprotons from annihilation.
One remaining challenge is cryogenics over long trips: as BASE-STEP leader Christian Smorra notes, if the journey takes too long, the system can eventually run out of liquid helium. The team is considering adding a generator to the transport vehicle to extend operating time.
Successful test with trapped protons – and what comes next
For the first full‑scale test, the collaboration used about 100 trapped protons instead of antiprotons. Protons are easier to handle but respond to electromagnetic disturbances in essentially the same way, making them ideal test particles.
The proton‑filled trap was loaded onto a truck and driven across CERN’s main site while the team monitored conditions in real time. The particles arrived with no losses, proving that the mechanical, cryogenic and vacuum design can survive real‑world transport.
BASE spokesperson Stefan Ulmer stresses why this matters: accelerator hardware in the AD hall generates magnetic‑field noise that limits precision. By moving antiprotons to calmer environments such as Heinrich Heine University Düsseldorf, the team aims for at least 100‑fold better precision in measurements of antiproton properties.
Such gains are crucial for tests of fundamental symmetries and for tackling one of physics’ biggest open questions: why the universe contains so much more matter than antimatter. The same technology could also be used to transport other exotic particles, including ultra‑highly‑charged ions, opening new options for precision experiments far from big accelerator halls.
