A compact X-ray machine launches its first lights


Electron accelerator of the ThomX installation at the IJCLab laboratory of the University of Paris-Saclay. This prototype machine interacts an electron beam with a laser beam to produce X-rays. PATRICK DUMAS/IN2P3/CNRS

A few steps from the banks of the Yvette, on the Orsay campus (Essonne) of the University of Paris-Saclay, a cylindrical building topped with a thick concrete dome towers 22 meters above the neighboring laboratories. Inside the “Igloo”, as it is nicknamed, a unique machine is in operation. ThomX is the world’s brightest and most compact X-ray Source, occupying more than 100 square meters, or about a quarter of the Igloo.

The instrument looks like a model electric train, with its circular shape and its “rails” placed 1 meter above the ground. The “cars” are electrons circulating in tubes, completing a circuit of 18 meters in 60 nanoseconds, at the speed of light. The “station” is a cavity made of mirrors in which infrared light from a laser is amplified by successive bounces in order to “hit” the electrons each in turn.

“We’re playing billiards”, summarizes Nicolas Delerue, CNRS researcher, one of the project leaders since 2010, to describe the so-called “inverse Thomson” physical effect. According to this principle, when colliding with photons from the cavity, electrons, like billiard balls, are slowed down and emit X-rays, sent to a neighboring room on targets. The latter could be master paintings or sculptures, where we would like to study the origin of colors or materials, as well as people or animals for medical imaging or therapeutic treatments.

New therapeutic avenues

ThomX is mainly the result of a collaboration between the Irène-Joliot-Curie Physics of Two Infinities Laboratory (IJCLab) at Paris-Saclay University, the Soleil synchrotron in Saclay, the European Synchrotron Radiation Facility (ESRF) in Grenoble , the Center for Intense Lasers and Applications (Celia) in Bordeaux and the company Thales, for a budget of around 15 million euros, according to its project manager, Kevin Dupraz, teacher-researcher at Paris-Saclay University. The project must demonstrate the feasibility of new equipment that can be installed in museum laboratories or hospitals, as a new option compared to the two other main ways of generating X-rays.

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In medicine, the latter are obtained according to the method of their discoverer, Wilhelm Röntgen, at the end of the 19th century.e century: an electron beam accelerated by a high voltage strikes a metal sheet, which emits photons, in a wide energy range, which pass through the soft tissues.

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