Dynamics of a microcapillary discharge plasma using a soft x-ray laser backlighter

Relativistic warm plasma theory of nonlinear laser-driven electron plasma waves

A relativistic, warm fluid model of a nonequilibrium, collisionless plasma is developed and applied to examine nonlinear Langmuir waves excited by relativistically intense, short-pulse lasers. Closure of the covariant fluid theory is obtained via an asymptotic expansion assuming a nonrelativistic plasma temperature. The momentum spread is calculated in the presence of an intense laser field and shown to be intrinsically anisotropic. Coupling between the transverse and longitudinal momentum variances is enabled by the laser field. A generalized dispersion relation is derived for Langmuir waves in a thermal plasma in the presence of an intense laser field. Including thermal fluctuations in three-velocity-space dimensions, the properties of the nonlinear electron plasma wave, such as the plasma temperature evolution and nonlinear wavelength, are examined and the maximum amplitude of the nonlinear oscillation is derived. The presence of a relativistically intense laser pulse is shown to strongly influence the maximum plasma wave amplitude for nonrelativistic phase velocities owing to the coupling between the longitudinal and transverse momentum variances.

Capillary discharge-driven metal vapor plasma waveguides

We report the generation of dense plasma waveguides containing a large concentration of silver ions by means of a fast (approximately 55 ns first half-cycle) microcapillary discharge. Concave plasma density profiles with axial electron density > 1 x 10(19) cm(-3) were measured from discharge ablation of 330 or 440 microm diameter Ag2S capillaries with 3-5 kA peak amplitude current pulses. The dynamic of this plasma waveguide was studied with interferometry, absorption measurements, and hydrodynamic model simulations. The results are relevant to the development of efficient longitudinally pumped metal vapor soft x-ray lasers, in particular those employing transient excitation of Ni-like ions. An approach to the design of a gain saturated wave-guided 13.9 nm laser in Ni-like Ag is discussed.

Nonlocal-thermal-equilibrium model of a pulsed capillary discharge waveguide

Slow pulsed capillary discharges are under investigation for use as plasma channel waveguides in laser-wakefield acceleration. In this study, we present a non-local thermal equilibrium (non-LTE) plasma model with a model for the wall temperature coupled to it. This model is used to describe an example of a slow pulsed capillary discharge, and the results are compared with experimental results. The agreement is satisfactory, indicating suitability of our model. Significant deviations from LTE are found during the formation of the plasma channel. The model is also used to study the influence of the discharge current on the guiding properties. It was found that this influence is small over most of the current range that was investigated.

Hamiltonian description of low-temperature relativistic plasmas

We develop a low-temperature fluidlike plasma model without recourse to a collisional closure. The equations are closed by treating the momentum spread asymptotically. This model inherits the Hamiltonian structure, including Casimir invariants of the Vlasov-Maxwell theory. We study temperature evolution in the wake of an intense laser pulse propagating in a plasma. We show that the momentum spread is intrinsically anisotropic and that, for conditions corresponding to recent experiments, modest heating occurs.

High-power-density capillary discharge plasma columns for shorter wavelength discharge-pumped soft-x-ray lasers

We report the generation of plasma columns in gas-filled capillary channels using discharge excitation powers that exceed those of previous studies by one to two orders of magnitude. Current pulses up to 200 kA and 10-90 % rise time of about 10 ns (current increase rate equivalent to 1.5 x 10(13) A/s) were utilized to excite plasmas in 3.3 and 4 mm diameter channels. Time resolved soft-x-ray spectra and pinhole images of the plasma were obtained. The experimental data and its comparison with model computations suggest that dense argon plasma columns 300 mum in diameter with electron temperatures >250 eV have been obtained. These characteristics make these plasmas of interest for extending discharge-pumped lasers to shorter wavelengths.

Simulations of a hydrogen-filled capillary discharge waveguide

A one-dimensional dissipative magnetohydrodynamics code is used to investigate the discharge dynamics of a waveguide for high-intensity laser pulses: the gas-filled capillary discharge waveguide. Simulations are performed for the conditions of a recent experimental measurement of the electron density profile in hydrogen-filled capillaries [D. J. Spence et al., Phys. Rev. E 63, 015401 (R) (2001)], and are found to be in good agreement with those results. The evolution of the discharge in this device is found to be substantially different to that found in Z-pinch capillary discharges, owing to the fact that the plasma pressure is always much higher than the magnetic pressure. Three stages of the capillary discharge are identified. During the last of these the distribution of plasma inside the capillary is determined by the balance between ohmic heating, and cooling due to electron heat conduction. A simple analytical model of the discharge during the final stage is presented, and shown to be in good agreement with the magnetohydrodynamic simulations.