High-temperature plasma of Ge generated by the PHELIX laser * M. M. Basko 1,2,3 , J. Maruhn 1,2 , An. Tauschwitz 1,2 , A. Grushin 3 , V. G. Novikov 3 , A. Frank 4 , V. Bagnoud 5 , and F. Hannachi 6 1 EMMI-GSI, Darmstadt, Germany; 2 University of Frankfurt, Germany; 3 KIAM, Moscow, Russia ; 4 Helmholtz-Institut Jena, Germany; 5 GSI, Darmstadt, Germany; 6 CENBG, France Certain nuclear transitions, accompanied by release of large amounts of energy, can be induced by appropriate atomic resonances. One potential candidate is an iso- meric state of 84 Rb, whose γ -decay could be initiated by resonant ns → 2s transitions in strongly (z ion > 27) ionized Rb atoms [1]. The required degree of ioniza- tion could be achieved by heating the medium, where the 84 Rb isomers are created, with the PHELIX laser at GSI. Since the Rb isomers are expected to be created in the 76 Ge(12C,p3n) 84 Rb reaction, i.e. by irradiating Ge with a carbon beam, it is the Ge plasma where one should demon- strate the ability to achieve the necessary temperatures un- der laser irradiation. Here we present the results of RALEF-2D [2] simula- tions of a 4 μm thick Ge foil, irradiated normally by a λ = 532 nm laser pulse of 150 J over a focal spot of ra- dius r f = 100 μm; the 1.4-ns long pulse was ramped with 0.2-ns linear rise and fall intervals. As a preliminary step, spectral opacities and the equation of state of Ge in the approximation of local thermodynamic equilibrium (LTE) were generated with the THERMOS code [3]. The RALEF runs were performed in the newly developed axial rz mode of the radiation transport, which was treated with 22 spec- tral groups and the S 12 angular quadrature. laser beam Figure 1: 2D color contour plot of Ge-plasma temperature (in keV) at t =0.8 ns. The calculated 2D temperature distribution in the Ge plasma shortly after the middle of the laser pulse (t = 0.8 ns) is displayed in Fig. 1. The corresponding 1D pro- files along the laser-beam axis are shown in Fig. 2. The laser heated plasma consists of two distinct zones: a low- density hot corona behind the critical surface, whose tem- perature reaches T max ≈ 1.3 keV, and a radiation-driven * The project is a collaboration between CENBG, CEA DAM, GSI, University of Frankfurt and KIAM and is supported by the Extreme Matter Institute EMMI. heat wave before the critical surface with a relatively high density of ρ ≈ 0.1–0.2 g/cc, where the matter and radia- tion temperatures are practically equal and lie in the range T ≈ T r ≈ 100–150 eV. The whole structure is dominated by x-ray energy transport: our simulation indicates that about 70% of the absorbed laser energy escapes the target in the form of keV-range x-rays. The calculated time- and space-integrated emission spectrum (in the direction oppo- site to the laser beam) is shown in Fig. 3. -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 5 10 15 20 25 30 35 40 ionization degree z ion z (mm) z ion z ion ρ 0.01 0.1 1 temperature (keV), density (g/cc) density T matter T radiation Figure 2: Profiles along the laser-beam axis at t =0.8 ns. 0.5 1.0 1.5 2.0 2.5 3.0 3.5 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 E ν [10 4 J/(ster keV)] hν (keV) Figure 3: Time- and space-integrated emission spectrum. Of principal interest for studying the nuclear transitions in Rb would be a narrow ablation front, where the mat- ter temperature jumps from T < ∼ 0.2 keV to T> 1 keV. It is within this layer that, similar to Ge, the admixture Rb atoms should undergo sharp increase in their ionization degree from z ion ≈ 15–20 up to a helium-like state with z ion = 35 assuming LTE. References [1] F. Gobet et al., Nucl.Instr. and Meth. A 653 (2011) 80. [2] M. M. Basko et al., GSI Report 2010-1 , p. 410. [3] A.F. Nikiforov, V.G. Novikov, V.B. Uvarov, Quantum- statistical models of hot dense matter: methods for compu- tation of opacity and equation of state, Birkh¨ auser, 2005. PNI-IONS-THEORY-08 GSI SCIENTIFIC REPORT 2012 354 FAIR@GSI brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by GSI Repository