Second generation of powerful X-ray laser fires for the first time
Scientists have achieved first light with an upgrade to one of the most powerful X-ray lasers the world has ever seen. The Linac Coherent Light Source (LCLS) images individual atoms and molecules by blasting them with intense X-ray bursts, and now its second phase of operations has begun.
The LCLS is what’s known as a hard X-ray free-electron laser (XFEL), an instrument that spans several kilometers in order to image the smallest objects in more detail than ever before. To do so, the machine accelerates a beam of electrons and directs them through an undulator, which is a series of magnets that makes the electrons wobble side to side. As they do, they throw off X-rays, which can then be amplified and used for a variety of experiments.
These bursts last just femtoseconds – millionths of a billionth of a second – so they can capture events that take place on incredibly fast time scales.
Since it first fired up in 2009, the LCLS has been used to image viruses, reproduce the conditions at the center of a star, trigger molecular cascading events, boil water into strange new plasma states, and create the kind of “diamond rain” that might fall on planets like Uranus and Neptune.
And now, it’s time for an upgrade. The second phase, or LCLS-II, will be able to double the power of the X-rays and produce far more pulses. The original could manage 120 X-ray pulses per second, but LCLS-II will ramp that up to a huge one million pulses per second.
Doing this requires a brand new undulator. The original has been removed and now replaced with two new systems, each made up of thousands of magnets. These will be able to distort the electron beams with the force of a few tons, without letting the surrounding structure move more than a hundredth the width of a hair.
Using these new undulator systems, scientists will be able to fine-tune the space between the magnets much more precisely than before, which will allow them to adjust the wavelengths of the X-rays produced.
The new system has now achieved first light. On July 17, the team fired a beam from the existing accelerator into the new undulator, successfully produced X-rays, and managed to finely tune the system to reach full X-ray laser performance.
This is just the first step towards LCLS-II though – the rest of the upgrade is due to be completed in the next two years. Along with the new undulators, a brand new accelerator is also being constructed. This will use cryogenic superconducting technology to get the electrons traveling at almost the speed of light.
Over the next few weeks, testing will be done on an array of optics that adjust the X-rays according to whatever experiments need to be done. After that, over 80 such experiments are due to be carried out over the next six months. And one of the first targets for study will be the SARS-CoV-2 virus.
The video below provides a closer look at the undulator.