We have reported the first observation of large soft-x-ray amplification in a discharge-created plasma. A gain coefficient of 0.6 cm " at 46.9 nrn was measured in a Ar-H 2 mixture, while higher laser intensities were reported in pure argon. It was later realized that the fraction of H 2 in the gas mixture experiments was, due to incomplete mixing of the gases, smaller than the 1:2 ratio reported, and amounted to less than 10%. Subsequent experiments have confirmed that larger amplification occurs in pure argon discharges, resulting in gain coefficients of up to 1.1 em -1.

No abstract

We present an analytical model for the Rayleigh-Taylor instability that allows for an approximate but still very accurate and appealing description of the instability physics in the linear regime. The model is based on the second law of Newton and it has been developed with the aim of dealing with the instability of accelerated elastic solids. It yields the asymptotic instability growth rate but also describes the initial transient phase determined by the initial conditions. We have applied the model to solid/solid and solid/fluid interfaces with arbitrary Atwood numbers. The results are in excellent agreement with previous models that yield exact solutions but which are of more limited validity. Our model allows for including more complex physics. In particular, the present approach is expected to lead to a more general theory of the instability that would allow for describing the transition to the plastic regime.

A new approach to the Rayleigh-Taylor instability is presented that yields exact solutions for the simplest cases and provides approximate but still very accurate analytical expressions for important and more complex cases involving nonideal fluids. The approach is based on Newton’s second law and allows for an intuitive and physically appealing explanation of the mechanisms underlying the instability.

We have reported the first observation of large soft-x-ray amplification in a discharge-created plasma. A gain coefficient of 0.6 cm " at 46.9 nrn was measured in a Ar-H 2 mixture, while higher laser intensities were reported in pure argon. It was later realized that the fraction of H 2 in the gas mixture experiments was, due to incomplete mixing of the gases, smaller than the 1:2 ratio reported, and amounted to less than 10%. Subsequent experiments have confirmed that larger amplification occurs in pure argon discharges, resulting in gain coefficients of up to 1.1 em -1.

High-temperature iT, > 150 e'V), small-diameter (--200 J..lm) plasma columns have been efficiently generated by very fast (13 ns rise time, 28 ns full width at half maximum) pulsed discharge excitation of capillary channels filled with preionized gas. Discharges in argon-filled capillaries at currents between 20 and 60 kA produced plasmas with Ar x-Ar XIV line emission, in which the degree of ionization was controlled by the magnitude of the current pulse. The characteristics of these plasmas differ from those created by vacuum discharges in the same capillaries and approach those necessary for soft-x-ray amplification in low-Z elements. PACS numberts): 52.80. -s, 42.55.Vc

We have reported the first observation of large soft-x-ray amplification in a discharge-created plasma. A gain coefficient of 0.6 cm " at 46.9 nrn was measured in a Ar-H 2 mixture, while higher laser intensities were reported in pure argon. It was later realized that the fraction of H 2 in the gas mixture experiments was, due to incomplete mixing of the gases, smaller than the 1:2 ratio reported, and amounted to less than 10%. Subsequent experiments have confirmed that larger amplification occurs in pure argon discharges, resulting in gain coefficients of up to 1.1 em -1.

The existence of various spatial distributions of hydrogen plasma in a pulsed 2.45 GHz microwave discharge is demonstrated. The data has been obtained through optical emission diagnostics utilizing an ultra-fast CCD camera system with multi-channel plate (MCP) intensifiers, and a wavelength-filtered photodiode recording temporal light emission signals of hydrogen atoms and molecules. It has been observed that the magnetic field topology and strength are determining the transitions between different plasma patterns and spectral saturation times while neutral gas pressure and microwave power show a weaker influence on the profiles but affect the emitted light intensity.