Researchers from Heinrich Heine University Düsseldorf and Forschungszentrum Jülich have confirmed “for the first time worldwide” that the polarization state of particles is preserved during laser-plasma acceleration.

This finding is relevant for various scientific applications, including controlled nuclear fusion. The preservation of polarization, which refers to the collective spin alignment of particles, was demonstrated for the first time using this specific acceleration method.

Conventional particle accelerators, such as those operated by CERN, are large-scale facilities that use magnets and radio-frequency cavities to accelerate particles over distances of several kilometers. Laser-plasma accelerators are emerging as a compact alternative that can be constructed at a lower cost. 

“These accelerators can achieve acceleration gradients up to around 1,000 times higher than those of conventional accelerators,” said the researchers in a press release.

Maintenance of spin alignment is significant

A research team led by Professor Markus Büscher has now shown that despite these high gradients, the spin alignment of the particles remains stable.

The maintenance of spin alignment is significant because it influences how particles interact. In the field of controlled nuclear fusion, the probability of a reaction increases when the spins of the fusing nuclei are aligned in parallel.

“Spin alignment is crucial to a range of fundamental scientific questions as it influences the interaction between particles,” explained Professor Büscher.

If the spins of the nuclei used as fuel are correctly aligned, the energy output of a fusion reactor can be increased. The confirmation that laser-plasma accelerators do not disrupt this alignment makes them a viable tool for fusion research.

“In controlled nuclear fusion, the reaction probability – and thus ultimately the energy produced in the reactor – increases significantly when the spins of the fusing nuclei, the ‘fusion fuel’ so to speak, are aligned in parallel,” added Professor Büscher.

To verify these results, the researchers conducted experiments using Helium-3, an isotope of the noble gas helium. The process required the daily generation of pre-polarized Helium-3 gas at Forschungszentrum Jülich.

Using high-power laser to accelerate ions

This gas was transported in specialized containers to the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. At this facility, the team used the PHELIX high-power laser to accelerate the ions.

They then analyzed the particles using CR-39 detector plates to confirm that the degree of polarization was maintained throughout the process.

These findings also have implications for the acceleration of protons and electrons. Scattering polarized electrons with protons and neutrons can provide detailed information regarding the structure of matter and fundamental interactions.

“They are particularly well-suited for investigating the physics beyond the Standard Model, for example to generate the possible candidates for ‘dark matter’ known as axions,” asserted Professor Büscher of possible future uses.

The study establishes that laser-plasma accelerators can preserve the polarization of particles, a result that supports the use of compact technology in high-energy physics.

“We were able to show for the first time worldwide that the polarization of 3He particles is preserved during laser–plasma acceleration. This is an important finding for use of this new acceleration technology in various fields of application,” concluded Büscher.