| The present record of laser intensity reached recently in laboratory conditions is 2 x 10 W /cm2 [1]. Due to the active work of international project Extreme Light Infrastructure (ELI) [2] this record is expected to increase by several orders of magnitude. According to theoretical estimations at intensities 10¯10 W /cm2 the QED effects of electron-positron pair production by hard photons may become important and result in massive production of QED cascades. This sort of cascades has revealed the new property of the restoration of energy and dynamical quantum parameter due to the acceleration of electrons and positrons by the field and may become a dominating feature of laser-matter interactions at ultra-high intensities [3]. It is therefore timely to study the kinetic transport equations from the numerical point of view in order to model relativistic plasma experiencing the quantum effects of high-energy radiation and pair productions. My talk comprises of two parts. The first is an introduction to the theory of QED cascades in laser plasma. An emphasis will be placed on the elementary cascade processes of hard photon emission and pair production in external field and somewhat less studied reverse processes of photon absorption and one photon pair annihilation [4]. Additionally, electron-electron, electron-photon scattering and two-photon pair creation/annihilation will be briefly addressed due to their anticipated importance for thermalization of electron-positron-photon plasma on longer then laser duration scales. The second part of presentation will be focused on numerical modeling of the whole cascade in the laser field starting from a seed particle till the saturation due to nonlinear response of arising electron-positron plasma. Both effects of hard photon radiation and electron-positron pair creation can relatively easy be incorporated into conventional plasma simulation codes by means the Monte-Carlo method [4, 5]. However, the equations describing relativistic plasma in nonlinear cascading regime may become stiff and then possibly unstable. As a cure for this severe problem we suggest to employ highly stable and accurate methods enabling adaptation of time and space resolution. The adaptivity is also a critical issue for handling of enormously growing electron-positron plasma. In fact, a number of real pairs can increase by the many order of magnitude before saturation due to plasma effects takes place. I will discuss how adaptivity in the phase space can be realized to keep computation requirements feasible for realistic cascading plasma modeling. Finally I will present the simulation results of electron-positron cascade in colliding laser pulses and discuss possible experimental implications. References [1] V. Yanovsky, et al., Opt. Express 16, 2109 (2008). [2] Extreme Light Infrastructure: Report on the Grand Challenges Meeting, edited by G. Korn and P. Antici (Paris, 2009). [3] Elkina N. V., Fedotov A. M., Kostyukov I. Yu., Legov M. V., Narozhny N. B., Nerush E. N. , and Ruhl H., QED cascades induced by circularly polarized laser fields, Phys. Rev. ST. Accel. 14, 054401 (2011). [4] A. I. Nikishov, V. I. Ritus, Sov. Phys. JETP 19, 529 (1964); 25, 1135 (1967). [5] Nerush E. N., I. Kostyukov I. Yu., Fedotov A. M., Narozhny N. B., Elkina N., and Ruhl H., Laser Field Absorption in Self-Generated Electron-Positron Pair Plasma, Phys. Rev. Lett. 106, 035001 (2011). |
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