Modern particle accelerators measure up to several kilometres in size and cost billions of euros. But thanks to a new method they could shrink to less than 10 meters and cost 10 times less in future. To this end, physicists at the Max Planck Institute of Quantum Optics in Garching accelerated electrons directly using a light wave. In the conventional procedure by contrast, particles are accelerated with microwaves. In their demonstration experiment, John Breuer and Peter Hommelhoff obtained an accelerating force that was equally as strong as the force achieved in current conventional particle accelerators. The unique feature of the Garching-based procedure is that it is modular and can be expanded into a multi-level system capable of accelerating charged particles – which could be protons or ions, as well as electrons – around 100 times faster than current systems, and therefore could be built to a much smaller scale. Developmental work is still necessary for this expansion, however.
Cost-effective, laboratory-scale particle accelerators measuring less than 10 meters would benefit the research community greatly. Many research groups regularly queue at the few linear accelerators in which a straight line of particles is accelerated almost to the speed of light. Smaller and less expensive accelerators, on the other hand, would be available in greater numbers and would lead to a growth in research and faster research results in areas such as nuclear physics, materials science and life sciences.
In order to be able to build more compact particle accelerators, the electric field driving the particles would have to be strengthened. This can be illustrated by a picture in which a car represents an electron, a street stands for the electric field and the gradient of the street corresponds to the strength of the field. A stronger electric field is then equivalent to a more steeply sloping street on which a rolling car gathers the same speed on a short stretch of road than it would on a long, flatter road. But it is almost impossible to increase the electric field with current technology. Metaphorically speaking, current accelerators are an incline with a limited gradient.
Breuer cites the easy scalability of the procedure as its most important advantage. This means that an accelerator can easily be expanded into a more high-performance system by concatenating multiple gratings. Another advantage is that the accelerated electron pulses can be controlled more precisely in terms of time. As the frequency of the driving light is significantly higher than that of microwaves, shorter electron pulses with higher frequencies can also be generated, stresses Breuer. According to the physicist, this effectively results in an extremely fast electron stroboscope which allows scientists to study rapid processes, such as changes in a crystal. "The method is also suitable for the construction of future, more cost-effective and more compact free electron lasers," adds Breuer. Such X-ray sources are also valuable research tools in materials science and biology.
However, even the accelerators or free electron lasers that are based on the new Garching method would have their limitations. They would generate a small flow of electrons and deliver a smaller beam diameter. The associated lower power of the X-ray light compared to today's conventional synchrotron sources can, however, be compensated for so that such innovative sources demonstrate better coherent properties – the light waves in their pulses vibrate more precisely in synchronisation than the waves of standard synchrotron radiation. This would enable scientists to conduct a whole range of new experiments, ranging from high-resolution tomography to the spectroscopy of atomic nuclei.