An important event in physics. miniature particle accelerator is working

The principle of simultaneous acceleration and beam confinement in a nanophotonic structure. a, A short, approximately 5 m long section of the two-column accelerator structure (grey). A laser light strike along the viewing direction induces an optical mode inside the structure that is driven by electrons (green). Up and down. Sketches of synchronous Lorentz force components F:f and: F:x: Acting on a projective electron, i.e., an electron synchronous with the propagating near-field mode and initially located in a phase s:=60, depicted as a green disk. Before the phase jump, the electron experiences an acceleration force (F:f positive). At the same time, the transverse forces act on the electrons in a transversely decentralized manner (F:x: negative for negative electrons x: coordinates, for example, see bottom left). After a sharp phase jump =120, the electron enters the same nanophotonic mode in the next macrocell, but is now phase shifted to s:=60 (top right). Also here the electron experiences an acceleration force (positive F:f), but now the transverse forces act in a concentrated manner (bottom right, see also c:). This is repeated with each laser field period, i.e. every 6.45 fs, which is imaged for multiple laser periods as the electron (green disk) propagates through the structure. Co-occurring longitudinal bunching and bunching are discussed in the main text. bImaging the phase jump from a focusing to a defocusing macrocell =240 (effectively 120), transferring the projective electron s:= from 60 s:=60. c:,d:Zooming in on relevant regions a and: brespectively, with arrows indicating the force field at one instant in time. e, Simulated trajectories of electrons as they move through the accelerator structure while gaining energy (color indicates instantaneous energy). The orange and purple blocks above depict the corresponding macrocells acting transversely, focusing (purple) and defocusing (orange). Credit: Nature (2023). DOI: 10.1038/s41586-023-06602-7

Particle accelerators are important tools in a variety of industries, research, and the medical sector. The space required for these machines varies from a few square meters to large research centers. Using lasers to accelerate electrons in a photonic nanostructure is a microscopic alternative that can produce significantly lower costs and make devices significantly smaller.

So far, no significant energy gains have been reported. In other words, it was not shown that the electrons really increased in speed significantly. A team of laser physicists at Friedrich-Alexander-Universitt Erlangen-Nrnberg (FAU) has now succeeded in demonstrating the first nanophotonic electron accelerator simultaneously with colleagues at Stanford University. FAU researchers have now published their findings in the journal Nature.

When people hear “particle accelerator,” most likely think of the Large Hadron Collider in Geneva, the roughly 17-mile-long loop tunnel that researchers from around the world have used to study unknown elementary particles. However, such massive particle accelerators are an exception. We are more likely to encounter them elsewhere in our daily lives, such as in medical imaging procedures or radiation to treat tumors.

Even then, however, the devices are several meters in size and are still quite bulky, with room for improvement in terms of performance. To improve and reduce the size of existing devices, physicists around the world are working on dielectric laser acceleration, also known as nanophotonic accelerators. The structures they use are only 0.5 millimeters long, and the channel through which the electrons are accelerated is only about 225 nanometers wide, making these accelerators as small as a computer chip.

The particles are accelerated by ultra-short laser pulses that illuminate the nanostructures. “The dream application would be to put a particle accelerator on the endoscope so we could deliver radiotherapy directly to the affected area inside the body,” explains Dr. Tom Kluba, one of the four lead authors of the recently published paper.

This dream may still be a long way off for the FAU Department of Laser Physics team led by Prof. Dr. Peter Hommelhoff and consists of Dr. Tom Kluba, Dr. Roy Shiloh, Stephanie Krauss, Leon Bruckner, and Julian Litzel, but they have now managed to take a decisive step in the right direction by demonstrating a nanophotonic electron accelerator. “For the first time, we can really talk about a particle accelerator on a chip,” says Dr. Roy Schillo.

Guiding electrons + acceleration = particle accelerator

More than two years ago, the team made its first major breakthrough. they succeeded in using the alternating phase focusing (APF) method from the early days of acceleration theory to control the flow of electrons in a vacuum channel over long distances. This was the first serious step towards building a particle accelerator. Now, all that was needed to get a lot of power was acceleration.

“Using this technique, we have now succeeded in not only directing electrons, but also accelerating them in these nano-fabricated structures half a millimeter in length,” explains Stephanie Krauss. While this may not seem like a big achievement to many, it is a huge success in the field of accelerator physics. “We got 12 kiloelectron volts of energy. That’s a 43 percent increase in energy,” explains Leon Bruckner.

In order to accelerate particles over such large distances (when seen at the nanoscale), FAU physicists combined the APF method with specially designed columnar geometric structures.

However, this demonstration is just the beginning. The goal now is to increase the power and electron current gain enough to make the on-chip particle accelerator sufficient for medical applications. For this to be the case, the power gain must be increased by a factor of approximately 100.

“To achieve electron currents at higher energies at the output of the structure, we will have to expand the structures or place several channels next to each other,” explains Tom Chluba of the next steps of the FAU laser physicists.

Additional information:
Tom Kluba, Coherent Nanophotonic Electron Accelerator, Nature (2023). DOI: 10.1038/s41586-023-06602-7.

Provided by Friedrich-Alexander University Erlangen Nuremberg

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