Dense Electron-Positron Plasmas and Ultraintenseγrays from Laser-Irradiated Solids

Abstract

In simulations of a 10PW laser striking a solid we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10 26 m −3 can be achieved, seven orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of gamma-rays of intensity 10 22 Wcm −2 , potentially the most intense gammaray source available in the laboratory. This absorption results in a strong feedback between both pair and γ-ray production and classical plasma physics in the new 'QED-plasma' regime.Electron-positron (e − e + ) plasmas are a prominent feature of the winds from pulsars and black holes [1,2]. They result from the presence of electromagnetic fields strong enough to cause non-linear quantum electrodynamics (QED) reactions [3] in these environments leading to a cascade of e − e + pair production [4]. These fields can be much lower than the Schwinger field for vacuum breakdown [5] if they interact with highly relativistic electrons (γ >> 1) [3]. Non-linear QED has been probed experimentally with lasers in two complementary ways:(1) with a particle accelerator accelerating electrons to the necessary γ and a laser supplying the fields [6-8]; or (2) with a laser accelerating the electrons and goldnuclei supplying the fields [9][10][11]. An alternative configuration, using next-generation high-intensity lasers to provide both the acceleration and the fields [12], has the potential to generate dense e − e + plasmas. Analytical calculations and simulations exploring this configuration have shown that an overdense e − e + plasma can be generated from a single electron by counter-propagating 100PW lasers [12][13][14][15]. Here we will show that such a plasma can be generated with an order of magnitude less laser power by firing the laser at a solid target, putting such experiments in reach of next-generation 10PW lasers [16].The dominant non-linear QED effects in 10PW laserplasma interactions are: synchrotron gamma-ray photon (γ h ) emission from electrons in the laser's electromagnetic fields; and pair-production by the multiphoton Breit-Wheeler process, γ h + nγ l → e − + e + , where γ l is a laser photon [3,17,18]. Each reaction is a strongly multiphoton process, the former process being non-linear Compton scattering, e − + mγ l → e − + γ h [19,20], in the limit m → ∞. Therefore, these reactions only become important at the ultra-high intensities reached in 10PW laser-plasma interactions. The importance of synchrotron emission is determined by the parameter η. This depends on the ratio of the electric and magnetic fields in the plasma to the Schwinger field [5] (E s = 1.3 × 10 18 Vm −1 ). For ultra-relativistic particles 17,18]. γ is the Lorentz factor of the emitting electron or positron, β is the corresponding velocity normalised to c and E ⊥ is the electric field perpendicular to its motion. As η approaches unity each emitted photon takes a ...

Charged particle dynamics in multiple colliding electromagnetic waves. Survey of random walk, Lévy flights, limit circles, attractors and structurally determinate patterns

“…Computer simulations presented in Gonoskov et al (2016), Gong et al (2017), Vranic et al (2017) show that the MCLP concept can be beneficial for realizing such important laser-matter interaction regimes as, for example, the electron-positron pair production via the Breit-Wheeler process (see Vranic et al 2017) and the high efficiency γ -ray flash generation due Charged particle dynamics in colliding electromagnetic waves 3 to nonlinear Thomson or multi-photon Compton scattering, as shown in Gonoskov et al (2016), Gong et al (2017). Another configuration for the generation of a γ -ray flash is a single laser pulse irradiating an overdense plasma target (see Nakamura et al 2012;Ridgers et al 2012;Corvan, Zepf & Sarri 2016;Levy et al 2016). The applications of the laser based γ -ray sources are reviewed in Gales et al (2016).…”

Synchrotron radiation, pair production, and longitudinal electron motion during 10-100 PW laser solid interactions

“…Emission of short wavelength radiation by non-linear Compton scattering from highly relativistic electrons starts to become important and the requirement that this emission be modeled in a quantum electrodynamically correct way leads to this new regime sometimes being called the QED-plasma regime. Some possible applications of lasers in this intensity regime take advantage of these processes to either act as a high brightness gamma-ray source 4 or even as a positronium factory 3 . At an intensity of 10 23 W/cm 2 the relativistic gamma factor of an electron quivering in the field of a 1.06 micron laser can be as high as 200 leading to a relativistically corrected critical density of 2 × 10 23 cm −3 .…”

Numerical investigation and potential tunability scheme on and stimulated pair creation from vacuum using high intensity laser beams

“…[54,55]. These processes include recollision of the generated e + − e − pairs with the high energy photons, radiation reaction effects, photon-photon interaction of the multiphoton Breit-Wheeler mechanism, for which extensive investigations have been reported elsewhere [54][55][56][57][58] , and are beyond the scope of the present work.…”