Optical and electrical diagnostic of underwater Zn-wire explosion

Summary form only given. Study of hot dense plasma is very attractive from a few reasons. E.g. it is a source of EUV/soft X-ray radiation. Moreover, if one dimension of this plasma is significantly larger than the other two, and if this shape is quasi-stable, it can even amplify its spontaneous emission, which may result in EUV/soft X-ray lasing. Such elongated plasma can be easily (but expensively) generated by powerful linearly-focused visible/infrared lasers. In comparison with that discharge plasma sources are much cheaper, but they deliver the required energy into plasma during longer time and, therefore, have very often problems with “stability”. That´s why pinching discharges are usually closed in capillaries and this “proximity-wall stabilization” turns to be very efficient. However, for amplification of shorter wavelengths (below 25 nm) the discharge has to burn in metal vapors, which are difficult to feed into a capillary. As a solution we have suggested wire explosion in liquid, at which a capillary with liquid wall is created. The underwater Zn-wire explosion is currently performed in our laboratory in WEX (Wire EXplosion) device, consisting of power source (Marx-generator-fed co-axial pulse-forming line with closely-coupled spark gap (U_max ~ 500 kV, rise time τ~ 100 ns). To the spark gap it is attached a water-filled experimental chamber with exploding wire; this arrangement enables visible spectroscopy in radial direction. At the grounded end of exploding wire a special isolating part is placed, which creates interface between water-filled experimental chamber and evacuated diagnostic part, making possible not only visible spectroscopy, but also EUV/soft X ray measurement by PIN-diode, by EUV spectrograph, ...). A Rogowski coil is used for monitoring of the current waveform. Physical processes connected with wire explosion (current density and thermal diffusion from wire periphery to the wire axis, w- re melting, evaporation, and boiling, plasma channel formation, ...) are mathematically modeled and compared with experimental results.