A team of researchers from the University of Michigan has demonstrated the effects of radiation reaction by hitting electrons with an ultra-intense laser. This makes the electrons shake so violently, generating so much energy, that they actually slow down or stop. Results from the study are published in the journal Physical Review X.





Scientists believe that radiation reaction occurs around objects such as black holes and quasars. So, being able to measure this in the lab is a huge success. The way in which the researchers observed the radiation reaction was by colliding an ultra-intense laser with a high-energy beam of electrons. This was done through the use of the Gemini laser at the Science and Technology Facilities Council’s Central Laser Facility in the UK.

“We knew we had been successful in colliding the two beams when we detected very bright high energy gamma-ray radiation.,” confirmed Stuart Mangles of the Department of Physics at Imperial College London and senior author of the study. “The real result then came when we compared this detection with the energy in the electron beam after the collision. We found these successful collisions had a lower than expected electron energy, which is clear evidence of radiation reaction.”





By colliding the two beams together, the researchers create extremely strong magnetic fields. The researchers are using these areas of extremely strong fields as it enables them to better test their predictions. The way in which the team made the electron beam small enough to be able to interact with the intense laser was through a process called “laser wakefield acceleration.”

Laser wakefield acceleration involves firing a separate intense laser pulse into a gas. When this happens the gas transforms into plasma, creating a wave called the Wakefield The plasma’s electrons then surf this wake, obtaining very high energies within a very short distance.

These experiments are the start of a range of high-intensity laser projects that will delve deeper into the use of quantum theories. Moving forward the team will look to complete similar experiments but at much higher intensities or with higher energy electron beams. Keegan Behm is a is a U-M doctoral student who, working under the supervision of U-M’s Alec Thomas and Karl Krushelnick, used the gamma-ray diagnostics to confirm the presence of radiation reaction. Using a $2 million Major Research Instrumentation grant from the National Science Foundation, Thomas will be looking to carry out further, more powerful experiments.





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