On the behavior of micro-spheres in a hydrogen pellet target

Abstract

A pellet target produces micro-spheres of different materials, which are used as an internal target for nuclear and particle physics studies. We will describe the pellet hydrogen behavior by means of fluid dynamics and thermodynamics. In particular one aim is to theoretically understand the cooling effect in order to find an effective method to optimize the working conditions of a pellet target. During the droplet formation the evaporative cooling is best described by a multi-droplet diffusioncontrolled model, while in vacuum, the evaporation follows the (revised) HertzKnudsen formula. Experimental observations compared with calculations clearly indicated the presence of supercooling, the effect of which is discussed as well.

Compact cryogenic source of periodic hydrogen and argon droplet beams for relativistic laser-plasma generation

“…The increase of δr with increasing z (Fig. 3) results from the interaction of the droplets with the coexpanding gas prior to vacuum injection 23 , as evidenced in our case by the steeper increase of δr for the hydrogen droplets than for the much heavier argon droplets. This is further confirmed by the observation of spatially more stable hydrogen droplets produced without external gas atmosphere, as shown by the open symbols in Fig.…”

“…1(b)). This feature thus allows significantly reducing the interaction time of the droplets with the co-flowing gas, which is held responsible for the degradation of the droplet spatial stability observed in previous studies 23 . The compact size of our source would greatly facilitate the droplet beam opera- tion in a vacuum environment characterized by the presence of many delicate optical components as typically encountered in laser-plasma generation experiments.…”

“…The expanding liquid filament thus rapidly cools below its normal melting point and freezes well before Rayleigh breakup can take place 6,22 . The jet freezing can be circumvented by expanding the liquid into an atmosphere of the respective gas before injecting the resulting droplet stream into vacuum, a that has enabled the production of hydrogen droplet beams for applications in nuclear physics research in a storage ring 23,24 . However, the droplet sources employed in these studies are characterized by extended dimensions and a substantial loss of the spatial synchronization of the triggered droplet beam on the vacuum side 23 , crucial features that preclude their use in experiments in which pulses from a high-power laser are focused to a micro-scale spot.…”

Dynamics of Cryogenic Jets: Non-Rayleigh Breakup and Onset of Nonaxisymmetric Motions

“…Even the simple case of jets emanating from a vibrating nozzle leads to a broad spectrum of drop sizes, and the existence of satellite drops [7]. However, for technologies like ink-jet printing [8], for laser-plasma UV sources [9], for compact laser-based particle accelerators [10], accelerator experiments [11], or for space operations [12], the drop sizes and rates must be highly homogeneous.…”

Probing near-solid density plasmas using soft x-ray scattering

“…The controlled production of microscopic streams of a material is an ongoing effort in several fields. Besides providing scattering targets for particle accelerators [28,29], similar sources using xenon, water or liquid metal jets were investigated for generation of plasma EUV radiation [30]. Generally, the principle of operation is to press a fluid through a small orifice into the vacuum in a way that a continuous liquid filament is formed.…”