Thirty years ago, theorists John Dawson and Toshiki Tajima proposed an idea for making them thousands of times smaller: surf the particles on plasma waves driven by short intense laser pulses. Since plasmas are free of the damage limits of conventional accelerators, much larger fields can be built up within such waves, enabling much smaller accelerators.
Just five years ago, experimentalists finally demonstrated that such laser-plasma accelerators could produce monoenergetic, collimated electron beams with quality comparable to conventional accelerators. The secret was for the laser to produce a "bubble" almost completely devoid of electrons in its immediate wake that captured electrons from the surrounding plasma and accelerated them in an exceptionally uniform way. Yet the precise mechanism by which the bubble captured these electrons and accelerated them with such uniformity has remained one of the outstanding mysteries of this field.
Now new theoretical work by scientists from the University of Texas and Commissariat à l'Énergie Atomique (CEA, France), to be reported at the 2009 APS Division of Plasma Physics Annual Meeting, has shed light on this mystery. Formation of the exceptional quality electron beam is attributed to the evolution of the bubble shape which, in turn, is directly associated with the nonlinear evolution of the driving laser pulse (nonlinear focusing and defocusing).
The basic premise of this work is that the size of the bubble—the cavity of electron density traveling over the positive ion background with nearly the speed of light—is determined by the spot size of the driving laser pulse. Plasma nonlinearities cause the laser to focus and defocus in the course of propagation. Once the laser diffracts, the bubble expands. Electrons that constitute a dense electron shell surrounding the bubble move with relativistic speeds and thus have high inertia. As a consequence, some of them become too heavy to follow the expanding shell; they fall inside the bubble, stay inside till the end of the plasma (i.e. get trapped) and finally gain multi-GeV energy. The trapped charge is proportional to the bubble growth rate. Once the laser becomes self-guided, and the spot size oscillations saturate, the injection process clamps. Simultaneously, longitudinal non-uniformity of the accelerating gradient equalizes the trapped electron energy. This scenario of self-injection and monoenergetic bunch formation is discovered and explored in fine detail in the 3-D particle-in-cell simulations. This is fundamentally different from the previous work which concentrated on either one-dimensional models of electron trapping or on the reduced description of transverse plasma wave breaking in planar 2-D geometry.
The discussed mechanism of electron self-injection is very robust in experiments with the high-power laser (tens of terawatts to petawatt). In addition, an appropriate modification of the plasma density (e.g. using a thin dense slab as a nonlinear lens for the laser) may cause the laser to self-focus and defocus faster, which results in a single self-injection event. This kind of laser beam manipulation may lead to the generation of a 2.5 GeV mono-energetic (~1% energy spread) electron bunch containing ~1010 electrons in a future experiment with the recently commissioned Texas Petawatt (TPW) laser – the most powerful laser in the world. Electrons with 2.5 GeV of energy are traveling at 99.999998% of the speed of light. Electron beams with such unique properties are clearly beneficial for medical applications, radiation physics, material science, and homeland security (see, e.g., talks TO4.00004 and TO4.00005, this Meeting).
Saralyn Stewart | EurekAlert!
Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1
21.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR
Taming chaos: Calculating probability in complex systems
21.03.2018 | American Institute of Physics
An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.
The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...
In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.
Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...
Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.
They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...
A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...
For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.
In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...
19.03.2018 | Event News
16.03.2018 | Event News
13.03.2018 | Event News
22.03.2018 | Trade Fair News
22.03.2018 | Earth Sciences
22.03.2018 | Earth Sciences