Radiation reaction when a light-speed electron beam collides with a high-intensity laser

March 8, 2018, CORDIS

Electromagnetic radiation is pervasive. It comes in many forms, including radio waves, microwaves and high-energy X-rays and gamma rays. But what, precisely, is it?

Electromagnetic is the energy emitted by a charged particle such as an electron when it accelerates. When the accelerating particle releases this energy, it experiences a recoil force called a radiation . Normally, radiation reaction forces are too small to consider, but they do become significant in laser-plasma interactions and astrophysical contexts, where high-electromagnetic fields and high-electron energies come into play.

A paper published in the journal Physical Review X presents evidence of a radiation reaction occurring when a high-intensity laser pulse collides with a high-energy electron . A team of scientists supported by the EU-funded TeX-MEx and SF-QFT projects conducted this experiment using the Astra Gemini laser belonging to the Central Laser Facility in the United Kingdom.

The dual-beam Astra Gemini laser generates two synchronised laser beams, which together deliver a quadrillion (10¹⁵) watts of power. In the experiment, one laser pulse was used to produce a bunch of high-energy electrons through a process known as laser-wakefield acceleration, while the second laser was directed at the electron bunch. When the electron beam and laser pulse collided, the electrons oscillated in the second laser's electromagnetic field and scattered the laser beam's photons, which were detected as . The electrons' energy loss also resulted in a radiation reaction.

The difficulty of achieving a collision may be better appreciated if we consider the fact that laser pulses are thinner than a human hair and, with each lasting 45 quadrillionths of a second, had to hit what one of the scientists described as "micron-sized electron bullets" traveling at near-light speed. A collision was thought to be successful when high- gamma radiation was detected. Taking these infinitesimal speeds and widths into account, together with added factors such as variations from shot to shot and laser pointing and timing, it's quite clear why only a small number of collisions were successful.

The measurements obtained were used to compare quantum and classical models of radiation reaction. It was found that classical models tended to overestimate radiation reaction forces and gamma ray energies compared to quantum models. It was also concluded that the data was more consistent with a quantum electromagnetic model, but the fact remained that this only occurred slightly over 68 percent of the time and further studies were needed to properly assess different models.

The project team's main challenge going forward is to combine high- intensities, beam stability and high beam energies simultaneously in future experiments in order to gather enough data for a systematic study of quantum radiation reaction.

Explore further: Intense laser experiments provide first evidence that light can stop electrons

Related Stories

Reaching new heights in laser-accelerated ion energy

February 20, 2018

A laser-driven ion acceleration scheme, developed in research led at the University of Strathclyde, could lead to compact ion sources for established and innovative applications in science, medicine and industry.

When electrons ride a wave

September 8, 2017

Conventional electron accelerators have become an indispensable tool in modern research. The extremely bright radiation generated by synchrotrons, or free electron lasers, provides unique insights into matter at the atomic ...

FLASHForward accelerates first electron bunches

February 28, 2017

The plasma accelerator project FLASHForward achieved an important milestone in January: for the first time, the facility's high-power laser accelerated electron bunches in a plasma cell. Later in the operational phase, the ...

Recommended for you

How a particle may stand still in rotating spacetime

May 25, 2018

When a massive astrophysical object, such as a boson star or black hole, rotates, it can cause the surrounding spacetime to rotate along with it due to the effect of frame dragging. In a new paper, physicists have shown that ...

Long live the doubly charmed particle

May 25, 2018

Finding a new particle is always a nice surprise, but measuring its characteristics is another story and just as important. Less than a year after announcing the discovery of the particle going by the snappy name of Ξcc++ (Xicc++), ...

How can you tell if a quantum memory is really quantum?

May 23, 2018

Quantum memories are devices that can store quantum information for a later time, which are usually implemented by storing and re-emitting photons with certain quantum states. But often it's difficult to tell whether a memory ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.