The fast ignition concept has been conceived as an alternative to other approaches for nuclear fusion energy. In the fast ignitor scenario a high-energy particle beam, driven by an ultrashort pulse laser, is deposited into a pre-compressed deuterium-tritium (DT) fuel capsule and creates a 'hot spot' with temperature and density parameters suitable for ignition, approximately 10 kiloelectron volts (keV).
Initially, the easiest path for ignition was taken using electrons, but it was soon recognized that numerous problems such as instabilities exists. The next logical step was to use ions, more specifically, protons. Subsequent experiments demonstrated that protons could be accelerated to relevant energies with conversion efficiencies of 5 to 10 percent and they were proposed as an alternative to relativistic electrons. However, the number of protons required for fast ignition is in order of magnitude two times greater than that of light ions that have a conversion efficiency of laser energy into ions of up to 25 percent.
"Presently, all efforts in the direction of fast ignition focus entirely on protons, but this continues to be plagued by problems," said Dr. Jack Davis. "Our research strongly indicates that the use of light ions, heavier than protons, in the lithium to aluminum range is a path in the right direction for ignition."
For ions of the appropriate range, the beam energy can be deposited directly in the fuel, with high efficiency. In general, ion beams offer the advantage of more localized energy deposition, improved beam focusing, straight line trajectory while traversing the DT fuel, maximum energy deposition at the end of their range and suppression of the various kinds of instabilities.
The Ion stopping power — the gradual energy loss of fast particles as they pass through matter — results in a quadratic increase in the required ion kinetic energy relative to atomic number, but a decreasing number of these ions is needed to deliver the fast ignition hot spot energy, translating into a decreased irradiated spot size on the coupling target. The ionization density (number of ions per unit of path length) produced by a fast charged particle along its track increases as the particle slows down. It eventually reaches a maximum called the Bragg peak close to the end of its trajectory. After that, the ionization density dwindles quickly to insignificance.
Other considerations such as tailoring the ion energy and angular distribution, which are responsible for ion beam focusing and energy density deposition in time and space, may turn out to be more important for the practical realization of the fast ignition.
Daniel Parry | EurekAlert!
What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin
Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
19.07.2018 | Materials Sciences
19.07.2018 | Earth Sciences
19.07.2018 | Life Sciences