Contact

Porträt Prof. Dr. Cowan, Thomas; FWK

Prof. Dr. Thomas Cowan
Director Institute of Radiation Physics
Head High Energy Density
t.cowan@hzdr.de
Phone: +49 351 260 - 2270
Fax: +49 351 260 - 3700

Particle-in-Cell Simulations

During short pulse high power laser solid matter interactions, a significant fraction of laser pulse energy is absorbed to generate an intense beam of fast electrons with relativistic kinetic energies near the critical density surface. The transport of the intense fast beam into the solid target is of fundamental importance to many complex dynamics such as plasma oscillation, heating, ionization, instability, electric field and magnetic field generation, photon emission and so on. Here we focus on numerically investigating the ultrafast plasma dynamics for ion heating in buried layer targets [1], bulk electron heating [2], collisional ionization [2,3], transport instability and quasi-static magnetic generation from PIC simulations. In order to connect the complex plasma dynamics seen in PIC simulations with experiments, we further study the role of in-situ synthetic diagnostics that mimic experimental diagnostics. As one key example we propose to use X-Ray Free Electron Lasers for probing the density modulations and ionization dynamics in the bulk target by small angle X-ray scattering which allows for femtosecond and nanometer resolution of transient plasma processes. We also investigate the feasibility to probe self-generated MegaGauss magnetic fields associated with the transport instability of the laser accelerated hot electrons using Faraday rotation method and so on. Developing Faraday rotation diagnostic technique can also be used to detect the vacuum birefringence and thus is attractive for both high energy density community and quantum electrodynamics community. With these techniques, probing fundamental plasma properties will allow for direct comparison to simulations, challenging state of the art theoretical modeling of collisions, ionizations.

[1] L. G. Huang, M. Bussmann, T. Kluge, A. L. Lei, W. Yu, and T. E. Cowan, Phys. Plasmas 20, 093109 (2013).
[2] L. G. Huang, T. Kluge, and T. E. Cowan, Phys. Plasmas 23, 063112 (2016).
[3] T. Kluge, M. Bussmann, H.-K. Chung, C. Gutt, L. G. Huang, M. Zacharias, U. Schramm, and T. E. Cowan, Phys. Plasmas 23, 033103 (2016).  

 

Heating and Ionization


Non-Equilibrium Warm Dense Matter

We perform first principle quantum simulations for equilibrium warm dense matter to obtain quantities like the equation of state, opacity, conductivity, dielectric functions, (dynamic) structure of electrons and ions, ionization potential depression, and temperature relaxation times. We use real time Green's functions for the description of non-equilibrium warm dense matter states, in particular their time dependent structure and relaxation processes. Using these results, we build effective models that allow a simulation of x-ray spectra of warm dense matter as obtained in experiments allowing excellent and accurate comparison with measured
quantities.  

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Detector Development

Laser-matter interactions generate a very large amount of high-energetic particles. In a typical highintensity short-pulse experiment, about 10^10 bremsstrahlung photons with energy up to tens of MeV are generated in a single shot. The spectrum of these photons is directly related to the electron temperature in the plasma. We are developing an active, single-shot, high-repetition rate calorimeter to measure this spectrum. Additionally, the high number of photons presents a challenge for the detectors used to diagnose the interaction. Our groups is developing new techniques based on Silicon Photomultipliers with a fast power switching that allows the detector to be switched on immediately after the main MeV-photon pulse has passed avoid saturation. This will open the field to current standard nuclear experiment techniques.

  


Contact

Prof. Dr. Thomas Cowan
Director Institute of Radiation Physics
Head High Energy Density
t.cowan@hzdr.de
Phone: +49 351 260 - 2270
Fax: +49 351 260 - 3700