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  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 , 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 .
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Gennadiy Bagdasarov, Pavel Sasorov, Alexey Boldarev, Olga Olkhovskaya, Vladimir Gasilov, Danila Khikhlukha, Daniele Margarone, Georg Korn, Sergey V. Bulanov, Stepan S. Bulanov, Carlo Benedetti, Anthony J. Gonsalves, and Wim P. Leemans, "Plasma formation in noncircular capillary discharges (Conference Presentation)," Proc. SPIE 10241, Research Using Extreme Light: Entering New Frontiers with Petawatt-Class Lasers III, 102411F (Presented at SPIE Optics + Optoelectronics: April 26, 2017; Published: 29 June 2017); https://doi.org/10.1117/12.2266150.5464857823001.
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