Time-resolved study of the extreme-ultraviolet emission and plasma dynamics of a sub-Joule, fast capillary discharge

Journal Article · Sat Aug 15 00:00:00 EDT 2015 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4927775· OSTI ID:22490087

Wyndham, E. S.; Favre, M. ^[1]

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1. Instituto de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Macul, Santiago (Chile)

In this work, we discuss experimental observations on the dynamics of a fast, low energy capillary discharge when operated in argon and its properties as an intense source of extreme-ultraviolet (EUV) radiation. The discharge pre-ionization and self-triggering were accomplished by the use of the hollow cathode effect. This allowed a compact size and low inductance discharge with multi-kA current level and a quarter-period of ∼10 ns at sub-Joule energy level. We used the novel moiré and schlieren diagnostics with a 12 ps laser to obtain the time evolution of the line electron density and to study the plasma dynamics. EUV spectroscopy and filtered diodes were also implemented to estimate the plasma temperature and density throughout the evolution of the discharge. EUV source size was measured by using a filtered slit-wire camera. We observed that EUV emission starts from a compressed plasma on axis during the second quarter-period of the current and continues until the fifth quarter-period. Ionization levels from Ar VII to X were observed. By comparing the EUV emission spectra with synthetic spectra, we found that at the onset of emission (∼7 ns), the plasma is well fitted by a single Maxwellian electron distribution function with T{sub e} ∼ 12 eV and n{sub e} ∼ 10{sup 17 }cm{sup −3}. Close to peak emission (∼13 ns), plasma temperature and density increase to ∼20 eV and n{sub e} ∼ 10{sup 18 }cm{sup −3}, respectively. However, in order to successfully match the experimental data, a two component electron distribution function was necessary. Later in time, a smaller fraction in the high energy component and higher temperature suggests homogenization of the plasma. The moiré and schlieren diagnostics showed multiple radial compression-waves merging on axis throughout the discharge; they are an important heating mechanism that leads to a period of severe turbulence at peak EUV emission. It was also observed that emission ceases when the axial maximum of the electron density collapses.

• OSTI ID: 22490087
• Journal Information: Physics of Plasmas, Vol. 22, Issue 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ARGON
CAMERAS
CAPILLARIES
DISTRIBUTION FUNCTIONS
ELECTRON DENSITY
ELECTRON TEMPERATURE
EMISSION SPECTRA
EV RANGE
EXPERIMENTAL DATA
EXTREME ULTRAVIOLET RADIATION
HEATING
ION TEMPERATURE
IONIZATION
LASERS
PLASMA
PLASMA DENSITY
SPECTROSCOPY
TIME RESOLUTION
TURBULENCE