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New generation of X-Ray lasers and particle colliders to be produced by Trojan Horse technique

Researchers have developed “super microscopes” to study nature on its primary level which can solve atomic and sub-atomic mysteries. They can investigate the smallest dimensions of matter with electron rays although it won’t work with visible light. It can be done either by directly using them in particle colliders or converting their energy to bright X-rays in X-ray lasers. Particle accelerators first produce electrons at source, then excite them through accelerator cavities.

Scientists from the SLAC National Accelerator Laboratory together with an international group of researchers have shown potentially much brighter plasma-based electron source suitable for use in powerful accelerators. Trojan horse technique is the process of releasing a beam of electrons from neutral atoms inside the plasma.

Bernhard Hidding from the University of Strathclyde in Glasgow, Scotland, the principal investigator of the study said that the Trojan horse method is experimentally proven and can be used for future electron sources. The research has been published in Nature Physics.

Currently, electrons are produced by shining laser light onto a metallic photocathode which pulls electrons out of the metal. Then the electrons are accelerated inside metal cavities where more energy is withdrawn from radiofrequency field resulting in a high-power electron beam. The ray results in the generation of very bright X-ray light in X-ray lasers such as Linac Coherent Light Source (LCLS) of SLAC.

Accelerators for high-energy beams become very large and costlier because the metal cavities can sustain only a specific energy gain over a certain distance before it collapses. Researchers at SLAC tried to make compact accelerators as they experimented substituting metal cavities with plasma which decreases the length of accelerators by 100 to 1000 times along with higher acceleration gradients.

Co-author Mark Hogan from SLAC mentioned that plasma acceleration can be very powerful but enhanced beams suitable for future use have not been produced yet which makes improving beam quality a top priority along with developing new forms of electron sources. The Trojan horse method could make electron beams 100 to 10,000 times brighter than the most powerful beams currently according to past estimation by researchers.

James Rosenzweig, co-author and principal investigator for Trojan horse project at the University of California, Los Angeles said that it is possible to build X-ray lasers with same power over few meters rather than a kilometer by uniting high acceleration and beam creation in plasma. The scientists conducted their experiment at Facility for Advanced Accelerator Experimental Tests (FACET) facility that produces high energetic electron pulses for research on future accelerator technologies, including plasma acceleration.

The researchers beamed laser light having enough energy to remove electrons off hydrogen into a mixture of hydrogen and helium gas turning neutral hydrogen into plasma which was not possible with helium where electrons stayed inside plasma being neutral. Researchers produced a plasma wake by sending one of FACET’s electron beam through the plasma similar to a motorboat generates a stir when gliding through the water, where the trailing electrons gain a high amount of energy. A lot of research needs to be done for making compact X-Ray lasers a reality with a need to improve their quality and quantity.

Vitaly Yakimenko, director of SLAC’s FACET Division said that these advancements can be done after FACET upgradation and FACET-II completion as it will be the only place in the world to generate beams with enormous intensity and energy because the experiment depends on the ability to use a powerful electron beam to produce the plasma stir.

Researchers destroyed the helium when the trailing electrons passed by, with a focused laser flash. Electrons after being pulled out of the helium atoms by a light pulse having enough energy were then accelerated in the stir. UCLA’s Aihua Deng, one of the lead authors said that it is important as well as challenging for the synchronization between the electron beam and laser flash running through the plasma with the speed of light to last merely a few millionths of a billionth second.

The generated electron will trouble the formation of plasma stir if the flash comes too early and plasma would have moved on and the electrons would not get accelerated if it comes too late. Oliver Karger, the other lead author said that the electrons knocked from helium gets quickly accelerated in the forward direction keeping the beam tightly packaged making this method transformative.

Research Paper: https://www.nature.com/articles/s41567-019-0610-9