Olga G. Olkhovskaya

Plasma formation in noncircular capillary discharges (Conference Presentation)

For several decades the capillary discharges have been under intensive investigations due to various promising applications, e.g. for the laser electron accelerators as well as for the X-ray lasers [1,2]. A major portion of the experiments were done with circular cross-section capillaries. An appropriate theoretical and numerical study of circular capillaries can be greatly simplified to a 1D model [3] assuming rotational and axial symmetries of the plasma flow in a long thin channel. On the other hand, studying capillaries with non-circular cross-section [4], which have been attracting substantially less attention, requires more complicated 2D models. Such capillaries, for example, square one, possess several advantages related to their fabrication as well as for plasma diagnostics The aim of our work is to compare the plasma density and temperature distributions formed at the quasistationary stage of the discharge. We present the results of MHD simulations of hydrogen-filled capillary discharges with circular and rectangular cross-sections under almost the same conditions characterizing the initial configurations and the external electric circuit. The simulation parameters are choosen to correspond to the capillary discharge based waveguide for the laser wakefield accelerator [5]. Bibliography [1] Leemans W. P. et al 2014 Phys. Rev. Lett. 113 245002 [2] Benware B. R. et al 1998 Phys. Rev. Lett. 81 5804 [3] Bobrova N. A. et al 2001 Phys. Rev. E 65 016407 [4] Gonsalves A. J. et al 2007 Phys. Rev. Lett. 98 025002 [5] Esarey E. et al 2009 Rev. Mod. Phys. 81 1229

MHD Simulation of Various Cross-Section Capillary Discharges

Our paper concerns with simulation of plasma dynamics in hydrogen-filled capillary discharge with circular and square cross sections under the same conditions. External domain with moderate size which is formed by a passive insulator was taken into account to perform these simulations. The general dynamics of plasma inside these capillaries are found to be quite similar to each other.

3D MHD simulation of capillary discharge for the BELLA project

Summary form only given. The project BELLA (LBNL, USA) is aimed to create an experimental facility for further advancing the development of laser-driven electron acceleration1. BELLAs unique attribute is the ability to use laser light to accelerate an electron beam up to 10 GeV level in a comparatively short distance of approximately one meter. The acceleration takes place during the propagation of a high power femtosecond laser pulse in the plasma formed in a capillary discharge. This capillary plasma forms a plasma channel able to guide the laser pulse, which in its turn forms a plasma wake wave that accelerates the injected electrons.To achieve a good coupling of a laser pulse with the capillary wave guide it is necessary to have a tool for the simulation of a 3D electron distribution inside the capillary, near the open ends of the capillary as well as near the channels supplying neutral hydrogen into the capillary. We use the MARPLE3D code2 to perform such simulations. MARPLE3D is an Eulerian numerical tool designed for simulations of radiative magnetohydrodynamic (MHD) problems related to experiments with magnetically driven high energy density plasmas. The simulations were performed at the supercomputer NERSK (LBNL, USA). Our main result that will be presented at the conference will concern 2D electron density distributions close to the open ends of the capillary.

3D MHD simulation of wire-array Z-pinch implosion under the action of high current pulse

The 3D radiative-magnetohydrodynamic code MARPLE (KIAM RAS) was applied to simulations of wire-array Z-pinch experiments on ANGARA-5-1 pulsed power facility (TRINITI, Russia). Different configurations of wire arrays accelerated by the current up to 3.5 MA (pulse rise time 100 ns) were investigated as soft X-ray sources.

Experimental and numerical study of a wire-explosion POS plasma dynamics

We study possibility to design fast current switch using wire explosion. It was carried out series of experiments on explosion of single wire connecting two coaxial cylindrical electrodes. Current with the amplitude value of 80 kA and rise time of 7 μs flow through the 4-μm tungsten wire. The outer magnetic field (up to 30 kG) was directed along the electrodes. Setup design allow to us to change the amplitude of current flowing between the electrodes and to measure the total resistance of interelectrode space. So we can study POS plasma dynamics with different currents (current amplitude is changed in range of 10-80 kA, current rise rate is changed in range of 109-1010 A/s) and magnetic field. We compare experimental data with results of simulations carried out by means of the 3D radiative magnetohydro dynamic code MARPLE 3D (KIAM RAS). We simulate (i) a stage of a wire explosion and plasma stirring in the inter-electrode gap, and (ii) a stage of a plasma switch performance. Numerical simulations allow to estimate a time we need to fill the volume between the coaxial electrodes with the plasma generated from the wire and switch inhomogeneity, and to study the switch dynamics dependence on the hydromagnetic instability as well as the Hall effect. The calculated switch evolution correlates with experimental data.