Kielfeld accelerator

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An electron beam creates a keel field in a lithium plasma

A wake field accelerator ( Wakefield Accelerator ; wake is the wake of a ship ) is a particle accelerator that uses a laser or electron or proton beam to generate a charged wave in a plasma path . Kielfeld accelerators are the subject of current research, so far (2017) they have not been used permanently in accelerator facilities. The possibility of this is to be investigated in the next few years by the FACET project at SLAC , the LAOLA project at the Deutsches Electron Synchrotron (DESY), JuSPARK at the Jülich Research Center and the AWAKE project at CERN . They could be made much more compact than other linear accelerators and could complement them in industry and medicine. Use in particle physics is also being investigated.

Comparison with other types of accelerators

In conventional particle accelerators, the electric field strength and thus the acceleration is limited by the dielectric strength . In order to achieve high energies, the acceleration sections must therefore be used multiple times, as in ring accelerators , or be very numerous in linear accelerators . A Kielfeld accelerator circumvents this limitation: It uses a plasma in which a laser or a particle beam excites a plasma wave in which high electrical field strengths prevail. This wave travels through the plasma at almost the speed of light . A correspondingly faster particle beam can therefore ride this wave like a surfer and is continuously accelerated. In experiments, the energy of particles can be increased by 1 GeV over a distance of 1 cm and by 50 GeV over a distance of 1 m. Other accelerator types require distances of 30 meters and more for 1 GeV. In addition to the maximum energy, it is also important that the energy of the accelerated particles is as uniform as possible and that the beam is easy to focus.

Working principle

If you shoot a very short electron beam into a plasma, these negatively charged electrons repel the electrons of the plasma and attract the positively charged ions. This creates a positively charged area behind the beam, which attracts the electrons that were previously repelled. They condense again so that the area is negatively charged and therefore repel each other again. This process happens several times with decreasing intensity, so that a wave of areas of positive and negative charge spreads through the plasma. There is a strong electric field between the areas in which the particles to be accelerated are accelerated.

With a proton beam, a wave is created in the same way, here the electrons are first attracted instead of repelled. Since the energy transfer to the beam to be accelerated depends on the energy of the wave-generating beam and protons can be brought to high energies more easily than electrons, electrons can possibly be accelerated to very high energies in this way. A corresponding experiment ("AWAKE") is currently being planned at CERN and will be set up by 2016. Due to their higher mass, protons can be brought to high energies more easily, since they emit less synchrotron radiation in synchrotrons . This high energy is then to be transferred to electrons using a Kielfeld accelerator.

A beam of photons from a laser can also be used. This primarily drives the electrons apart, so it works similar to an electron beam.

In order for the accelerated beam to remain permanently in the range of the optimal acceleration, its speed must be close to the speed of the shaft and must not change too much during the passage. Therefore, protons can only be accelerated with a Kielfeld accelerator if they already have a high energy and their speed is therefore close to the speed of light. Due to their low mass, electrons reach the required speed much faster and can therefore also be obtained from the plasma itself.

Development successes

The acceleration of electrons to the energy of 4.2 GeV with this technique was successful in 2014 at the Lawrence Berkeley National Laboratory . Similar success was achieved at the Stanford Linear Accelerator Center . In 2018, the electron energy in Berkeley was increased to 7.8 GeV. Two laser pulses were used for this, one to heat the plasma and a second pulse to accelerate it.

In 2016, a research group in France succeeded in using a relatively compact apparatus to generate electron beam pulses with an energy of 5 MeV based on this principle. The pulse duration is only about 1 femtosecond with a repetition frequency in the kilohertz range.

In 2018, researchers at AWAKE reported on the first electrons accelerated with a proton beam. With a gradient of 200 MV / m, an electron energy of 2 GeV was achieved.

literature

F. Hinterberger: Physics of Particle Accelerators and Ion Optics . 2nd edition, Springer, 2008, ISBN 978-3-540-75281-3 , p. 79

swell

Web links

Individual evidence

  1. ↑ Wakefield accelerator: surfing in the particle accelerator. In: www.spektrum.de. Retrieved December 5, 2015 .
  2. ↑ Pro-Physik.de: Compact electron slingshot
  3. ^ WP Leemans et al .: Multi-GeV Electron Beams from Capillary-Discharge-Guided Subpetawatt Laser Pulses in the Self-Trapping Regime . Phys. Rev. Lett. 113, 245002, Dec. 2014
  4. ↑ weltderphysik.de: Kielfeld acceleration success 2014 at SLAC ( Memento of the original from December 8, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed December 3, 2015 @1@ 2Template: Webachiv / IABot / www.weltderphysik.de
  5. ↑ Laser 'Drill' Sets a New World Record in Laser-Driven Electron Acceleration. February 25, 2019, accessed February 26, 2019 .
  6. ↑ D. Guénot et al .: Relativistic electron beams driven by kHz single-cycle light pulses. Nature Photonics , April 2017, [1] , [2]
  7. ↑ AWAKE successfully accelerates electrons. August 29, 2018, accessed February 24, 2019 .