Oral Session 217 Point-Type Soft X-Rays Source Formed by Supersonic Gas Jet 1 O.G. Olkhovskaya , A.S. Boldarev, V.A. Gasilov, S.V. Dyachenko, E.L. Kartasheva, G.A. Bagdasarov, A.Yu. Krukovsky, V.G. Novikov*, A.D. Solomyannaya*, D.A. Kim*, I.Yu. Vichev*, V.V. Alexandrov**, G.S. Volkov**, V.I. Zaytsev**, and I.A. Barykov** Institute for Mathematical Modelling RAS, 4a, Miusskaya sq. Moscow, 125047, Russia Phone: 8(499) 972-38-55, Fax: 8(499) 972-07-23, E-mail: aann@yandex.ru *Keldysh Institute of Applied Mathematics RAS, 4, Miusskaya sq., Moscow, 125047, Russia **Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow region, 142190, Russia ______________ 1 The work was supported by RFBR (Project No. 06-08-00472-a). Abstract – We discuss the possibility of creation of soft x-rays sources with small spatial and temporal extent based on the high-current discharge in a supersonic gas jet, instead of commonly used X- pinch technique which implies the use of some wire configurations. The construction and parameters of the nozzle providing a gas density configuration similar to the wire X-pinch is proposed. The MHD modeling of the implosion of such a configuration is performed, as well as the modeling of the emitted x-ray spectra. Some experimental results are also presented. 1. Introduction In recent years, there has been renewed interest in pinches as sources of high power x-rays. By pinch creation, the different types of the loads are used, for example, multiwire liners, gas puff et al. The main differences of loads are the different initial distribution of pinch material. Gas puff method is provided more easy way for creation of the repetition source. The electrical explosion of a system of two (or more) crossing wires (X-pinch) is now a common method of obtaining the x-rays sources with very small spatial extent for various purposes in physical experiments. The substitution of the wire configura- tion by gas jet produced by a specially designed su- personic nozzle should be interesting, because it pro- vides more easy way to reconstruct the initial configuration for the next shot. For this purpose, the gas density distribution in the discharge gap must be like the density distribution in the case of the classical wire X-pinch. 2. Mathematical models Thus, the whole task of modeling of such a process is divided into two different tasks: the production of ini- tial density configuration and the modeling of its elec- trical implosion. In the first task, only the gas- dynamics processes are important. We solve the 2D axisymmetric Euler equations with use of finite vol- ume TVD approximation at unstructured meshes [1, 2]. The use of unstructured meshes helps us to dis- cretize the computational domains with comparatively complex geometry, for instance, when the computa- tional domain includes the inner cavity of the nozzle and some open space near the outlet section. For the modeling of electrical implosion of differ- ent loads, we use the MARPLE and RAZRYAD codes developed at IMM RAS. Both codes implement the two-temperature magnetohydrodynamical model with anisotropic dissipative processes and radiational heat transfer [3–5]. More recent MARPLE code also uses the unstructured meshes technique, that allows taking into account more detailed geometrical description of computational domain. When the MHD modeling is performed, we use the obtained spatial distribution of plasma parameters for more detailed modeling of emitted x-rays spectra. Full system of the level-population kinetics equa- tions including the processes induced by non- equilibrium radiation field is used for calculations with averaging over close energy levels [6]. We use the Regemorter approximation written in analytical form for dipole collisional excitations and, for simplicity, the same formula for nondipole excita- tions with adjusted oscillator strengths calculated in Born approximation. As radiative excitations, only dipole transitions were considered. For collisional ionization the Lotz formula was ap- plied and Kramers approximation was used for photoionization and photorecombination processes. The formulas for rates with accounting for effects in- duced by radiation field can be found in [7], p. 275 (see also [8, 9]). For inverse processes, similar averaging with using principle of detailed balance was made. Some inaccu- racies in such approach are not essential in our case. 3. Gas-dynamics modeling In the first stage of our investigation, our aim was to confirm the possibility in principle to create the “X- pinch-shaped” density configuration in a gas jet by means of gas-dynamical effects. Namely, we want to obtain a gas jet configuration with high density in the middle of the discharge gap near the axis, and com-