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Parameter study of a pulsed capillary discharge waveguide

Slow pulsed capillary discharges are currently under investigation for use as plasma channel waveguides in laser-wakefield acceleration and XUV generation. In this work, a parameter study is performed on this device using a combination of two models, namely a non-local thermal equilibrium (non-LTE) plasma model and a wall temperature model that is coupled to it. This model has been validated against experiments. In the present study, two parameters are varied, the initial density and the channel radius. These parameters have a strong influence on the guiding properties. The results of this parameter study can be summarized in a single, empiric formula describing the matched spot size as a function of the initial density and the channel radius. This formula is expected to give a good prediction of the matched spot size, provided that no wall ablation occurs, diffusion is limited and that the current pulse is sufficient in amplitude and duration for formation of a well-ionized, stable plasma. This has been verified for the parameter range studied here.