How do I build a particle accelerator

Kielfeld accelerator: Particle accelerator for everyone

Particle accelerators are useful in materials science, physics and chemistry, but also in biology and medicine, because they make it possible to research the smallest building blocks of life. However, they have one major disadvantage: they are enormous. In the USA, scientists have now set an energy record with the help of a novel accelerator principle: their Kielfeld accelerator is so small that it can be set up in any laboratory.

  1. QUNDIS GmbH, Mannheim
  2. Segeberg district, Hamburg

Conventional linear accelerators work in a very simple way: Charged particles are revved up by electric fields. Simply increasing the field strength does not help the engineers, because above a certain value they exceed the breakdown voltage. The higher the energy to be achieved, the longer the path of the particles must be. The SLAC accelerator of the American National Accelerator Laboratory needs around two kilometers to bring electrons from 0 to 20 GeV. The particles gain just 0.01 GeV per meter.

The particles move like surfers on a wave

The accelerator that a team of researchers is now presenting in the science magazine Nature, on the other hand, looks very different: it transmits 1.6 GeV to the electrons over a distance of just 30 centimeters. How did the physicists come up with this trick? The solution is hidden in the name of the technology. In a sense, the particles swim along in the keel of a fast-moving boat. You move like surfers on a wave.

The research community has long suspected that this principle could be used for miniature accelerators. However, there is a practical problem: unlike a surfer, physicists cannot simply wait until a wave happens to pass by, on which they let their electrons surf. You have to create this wave yourself. To do this, they test two different methods. Option 1 is a powerful laser. A high-energy laser beam crosses a plasma, i.e. a gas made up of ions and electrons. Its wake pulls the light electrons with it, while the ions stay behind. In this way, enormous electric fields build up in a very short time, which are 100 to 1000 times larger than in conventional accelerators.

How high the acceleration achieved depends, on the one hand, on the strength of the laser and, on the other hand, on the temporal accuracy with which the laser pulses arrive. In the specialist magazine Physics of Plasmas, researchers were recently able to show that the pulses do not have to come at the perfect moment. Just as a child doesn't always have to wait for the optimal moment when swinging, an incoherent laser field can also produce the necessary energy peaks. This gives the researchers the opportunity to use many weaker lasers together instead of an expensive super laser.

All surfers have to start at the same moment

In the science magazine Nature, researchers from the American National Accelerator Laboratory have now reported successes with a different technology: They let electrons surf in the field of another electron beam that is almost as fast as light. The difficulty here is that all surfers have to start practically at the same moment, because otherwise there is a very wide distribution of energy. A particle beam whose members have too different energies is of little use to research.

In this experiment, a 20 GeV electron beam from the SLAC linear accelerator served as the boat that generated the keel field. The researchers shared this in such a way that around half of the particles could swim on the wave of the other particles. These surfers received 1.6 GeV of additional energy over the minimal distance of 30 centimeters - and indeed, that is the real success, with a very narrow spectrum. It is hoped that if several of these miniature accelerators could be connected in series, energies could also be achieved with which physics could approach phenomena such as the Higgs boson (126 GeV) or dark matter.