Description
Supersonic gas jet nozzles are commonly used to produce under-dense targets for laser-plasma interactions, especially in laser wakefield acceleration experiments. In such experiments, it is ordinarily advantageous to have a smooth and flat density profile which is reproducible for consistent accelerator operation. For specific adaptations - including density transition injection, or betatron radiation enhancement - it can be helpful to also have stable density changes at reproducible positions within the gas flow.
We present an improvement on the classic design of these nozzles which allows for a more consistent ‘flat-top’ density profile across a wide range of backing pressures and gases. By ensuring a smooth curvature of the nozzle throat the length and angle of the nozzle can be adjusted while still producing a density profile free from unwanted variations.
We also present the introduction of a structural feature inside the nozzle - or ‘kicker’ - to allow the production of density features (additional peaks) within the flat-top plateau. This method for generating peak-and-plateau density profiles removes one source of fluctuation in laser-plasma experiments. Conventionally, such features are generated by inserting a blade into the flow, or using multiple adjacent nozzles. The former may lead to shot-to-shot variability, and the later can result in unwanted features where the flows overlap.