Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to ultraviolet (UV) and X-rays. The development of increasingly powerful radiation sources for high-energy photons of this type has been very successful over the last two decades.
Fig. 1: Illustration of the efficient Gamma-ray emission (blue) from an ultra-relativistic high-density electron beam (green) which splits into filaments while passing through a thin metal foil.
Synchrotrons and free-electron lasers produce high-intensity UV and X-rays for basic research or for a variety of applications. For the interaction with atomic nuclei, which are ten to a hundred thousand times smaller than atoms, it needs the even shorter-wave and higher-energy gamma radiation. To date, there are no efficient gamma-ray sources. However, these are of great interest for researchers because they would offer completely new, unprecedented opportunities: from the study of nuclear structure and exotic processes in nuclei to nuclear and medical applications.
Various methods have been proposed to generate intense gamma-rays with photon energies of several million electron volts (eV). For comparison, the energy of a photon of visible light is about 2 eV. All proposals are based on acceleration of electrons with an extremely powerful laser and subsequent conversion of the electron energy into gamma-rays.
One method of this type has been projected recently at the "Extreme Light Infrastructure" (ELI) in Romania: here, optical photons of a laser beam colliding with relativistic electrons are scattered up to gamma energies (Compton effect). However, the energy transfer efficiency is (like all other mechanisms discussed so far) low: only approximately 10% using a laser of the 10-petawatt class (1 petawatt = 10¹⁵ watt).
Physicists around team leader Matteo Tamburini of the department “Theoretical Quantum Dynamics and Quantum Electrodynamics” headed by Christoph Keitel at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg have proposed a novel mechanism: their model calculations show that up to 60% conversion efficiency can be achieved if a high-energy (2 billion eV) well-focused high-density electron beam is shot at a thin (0.5 mm) electrically conductive solid plate as a target.
Under "normal" circumstances, the electrons would produce the well-known "bremsstrahlung", as in an X-ray tube. Here, deflection and deceleration of the electrons at the atomic nuclei - as an accelerated movement of charged particles - leads to radiation emission according to the laws of electrodynamics. The energy of the emitted photons covers a broad spectrum up to the (maximum convertible) kinetic energy of the electrons as an upper limit.
At very high electron densities in the electron beam (comparable to the density of molecules in air), the target material starts to act back on the electron beam itself. As the main feedback, the free electrons the conductor form a counterpropagating current which compensates the penetrating electron beam. Both overlapping currents create strong electromagnetic fields and instabilities, causing the incident electron beam to break up into individual filaments (see the illustration in Figure 1). This, in turn, reinforces the self-generated fields, which cause violent accelerations of the ultra-relativistic electrons, ultimately leading to a gigantic emission of synchrotron radiation. This exceeds the usual bremsstrahlung by up to a factor of 1000 in "brilliance". This is a measure of the number of photons per time, area, energy interval and solid angle. The latter describes the bundling of the radiation in the forward direction.
Figure 2 shows the spectral brilliance as a function of the photon energy for the most efficient synchrotron sources (red), energy conversion via the Compton effect (yellow ELI) and for the new method (blue). Compared with ELI, more than two orders of magnitude both in brilliance and in gamma-ray energies could be expected. Another disadvantage of the Compton scattering is the difficulty of overlapping and synchronizing the laser and electron beams. Furthermore, the new method is very efficient - up to 60% of the energy of the electrons could be converted into gamma-rays. The duration of the ultrashort gamma-ray flashes – determined by the length of the electron bunches - could be shorter than 30 femtoseconds (1 femtosecond = 10⁻¹⁵ s).
The electron density required for the self-amplification of electromagnetic fields is a technical challenge. Conventional 200 terawatt lasers (1 terawatt = 10¹² watt) with a 1 to 10 hertz repetition rate (a few flashes per second) are routinely available for generating and accelerating ultra-relativistic electron beams, and the new method could operate even with 100-1000 times higher repetition rate. However, the electron density achieved so far in experiments is still a factor of 10 to 100 too low. The total electron flow would be sufficient, but a stronger focusing of the beam onto the target would be required for efficient production of gamma-rays. A typical target would be metal foil of about 0.5 mm thickness. Strontium was investigated in the simulation, but the type of metal is not critical - conventional aluminum should also be a suitable target material.
Giant collimated gamma-ray flashes
Alberto Benedetti, Matteo Tamburini, and Christoph H. Keitel
Nature Photonics (2018), doi:10.1038/s41566-018-0139-y
Dr. Matteo Tamburini
Division Hon.-Prof. Dr. Christoph H. Keitel
Max Planck Institute for Nuclear Physics
Phone: +49 6221-516-163
Dr. Bernold Feuerstein | Max-Planck-Institut für Kernphysik
APEX takes a glimpse into the heart of darkness
25.05.2018 | Max-Planck-Institut für Radioastronomie
First chip-scale broadband optical system that can sense molecules in the mid-IR
24.05.2018 | Columbia University School of Engineering and Applied Science
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences