Stability of liquid-nitrogen-jet laser-plasma targets

• Microscopic jets of cryogenic substances such as liquid nitrogen are important regenerative high-density targets for high-repetition rate, high-brightness laser-plasma soft x-ray sources. When operated in vacuum such liquid jets exhibit several non-classical instabilities that negatively influence the x-ray source's spatial and temporal stability, yield, and brightness, parameters that all are important for applications such as water-window microscopy. In the present paper, we investigate liquid-nitrogen jets with a flash-illumination imaging system that allows for a quantitative stability analysis with high spatial and temporal resolution. Direct and indirect consequences of evaporation are identified as the key reasons for the observed instabilities. Operating the jets in an approximately 100 mbar ambient atmosphere counteracts the effects of evaporation and produces highly stable liquid nitrogen jets. For operation in vacuum, which is necessary for the laser plasmas, we improve the stability by introducing an external radiative heating element. The method significantly extends the distance from the nozzle that can be used for liquid-jet laser plasmas, which is of importance for high-average-power applications. Finally, we show that laser-plasma operation with the heating-element-stabilized jet shows improved short-term and long-term temporal stability in its water-window x-ray emission.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

Electric heating elements

Electron sources

Evaporation

Fighter aircraft

Image resolution

Jets

Laser beams

Laser produced plasmas

Liquid nitrogen

Liquids

Luminance

Nitrogen

Nitrogen plasma

Plasma stability

Stability

Vacuum applications

X ray apparatus

X ray optics

Ambient atmosphere

High average power

High brightness lasers

High repetition rate

Quantitative stability analysis

Radiative heating

Spatial and temporal resolutions

Temporal stability

Plasma interactions

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