Electron-positron pair plasmas represent a unique state of matter, whereby there exists an intrinsic and complete symmetry between negatively charged (matter) and positively charged (antimatter) ...particles. These plasmas play a fundamental role in the dynamics of ultra-massive astrophysical objects and are believed to be associated with the emission of ultra-bright gamma-ray bursts. Despite extensive theoretical modelling, our knowledge of this state of matter is still speculative, owing to the extreme difficulty in recreating neutral matter-antimatter plasmas in the laboratory. Here we show that, by using a compact laser-driven setup, ion-free electron-positron plasmas with unique characteristics can be produced. Their charge neutrality (same amount of matter and antimatter), high-density and small divergence finally open up the possibility of studying electron-positron plasmas in controlled laboratory experiments.
An important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to ...decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%.
Ionization injection is a simple and efficient method to trap an electron beam in a laser plasma accelerator. Yet, because of a long injection length, this injection technique leads generally to the ...production of large energy spread electron beams. Here, we propose to use a shock front transition to localize the injection. Experimental results show that the energy spread can be reduced down to 10 MeV and that the beam energy can be tuned by varying the position of the shock. This simple technique leads to very stable and reliable injection even for modest laser energy. It should therefore become a unique tool for the development of laser-plasma accelerators.
Making pions with laser light Schumaker, W; Liang, T; Clarke, R ...
New journal of physics,
07/2018, Letnik:
20, Številka:
7
Journal Article
Recenzirano
Odprti dostop
The interaction of high intensity short pulse laser beams with plasmas can accelerate electrons to energies in excess of a GeV. These electron beams can subsequently be used to generate short-lived ...particles such as positrons, muons, and pions. In recent experiments, we have made the first measurements of pion production using 'all optical' methods. In particular, we have demonstrated that the interaction of bremsstrahlung generated by laser driven electron beams with aluminum atoms can produce the long lived isotope of magnesium (27Mg) which is a signature for pion (π+) production and subsequent muon decay. Using a 300 TW laser pulse, we have measured the generation of 150 50 pions per shot. We also show that the energetic electron beam is a source of an intense, highly directional neutron beam resulting from (γ, n) reactions which contributes to the 27Mg measurement as background via the (n, p) process.
Plasma discharge in the capillary is used to develop x-ray lasers, waveguides for high power laser pulses, and as active plasma lenses to focus high energy charged particle beams. Capillary ...discharges in the high repetition rate regime are of interest for applications that require large average values, such as luminosity and/or electric current of laser accelerated particles. In the present paper, we study the capillary discharge in the high repetition rate regime in connection with the ultrashort laser pulse guiding for laser electron acceleration. Using magnetohydrodynamic computer simulations and theoretical scaling, we investigate the filling of the capillary with the gas, the electric discharge development leading to outflow of the plasma from the capillary, and the recovery of gas distribution after the discharge end. In the next cycle, these processes are repeated. As a result, we found the characteristic cycle time, which determines the upper limit on the repetition rate allowed by the capillary parameters. In the case of the capillary discharges used for acceleration of sub-GeV electron beams, e.g., needed for compact free electron lasers, an upper limit on the repetition rate is approximately equal to 10 kHz.
Using an analytical model and computer simulation, we show that the wakefield driven by an ultrashort laser pulse in high-density plasma periodically reverses its polarity due to the carrier-envelope ...phase shift of the driver. The wakefield polarity reversal occurs on spatial scales shorter than the typical length considered for electron acceleration with the laser-wakefield mechanism. Consequently, the energies of accelerated electrons are significantly affected. The results obtained are important for the laser-wakefield acceleration under the conditions relevant to present-day high-repetition-rate laser systems.
In this paper we analyze the properties of the electron bunches produced in a laser-plasma acceleration experiment using a 10mm helium gas-jet with a longitudinal density profile characterized by a ...double peak structure. Data were taken at three different gas-jet backing pressures of 5, 8 and 15 bars, corresponding to plasma densities of 1.2–3.6×1019cm−3 in the peaks and 3.5–10×1018cm−3 in the central plateau. The highest energy peak is recorded at more than 450MeV, with average energies between 80 and 180MeV. Bunch divergence and pointing stability have been measured and are found to be very sensitive to the density. Fully 3D PIC numerical simulations confirm that laser intensity and plasma density of our set up are in the range where electron acceleration takes place by self-injection in a bubble-like structure. Analysis shows that after the first density peak, accelerated electrons propagate through the plateau and the second density peak without the driver, undergoing non-linear interaction with the background plasma.
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