Speaker
Description
Cluster-jet targets provide compelling advantages for a wide array of experimental investigations owing to their unique windowless configuration and internal design. A powerful state-of-the-art cluster target source, specifically designed and constructed for the future PANDA experiment at FAIR, has been successfully assembled and inte-grated with a dedicated target setup at COSY/Jülich [1,2]. This target system will play a decisive role in the up-coming KOALA experiment at the GSI in Darmstadt over the next years.
The target properties – including target thickness, width, cluster sizes [3], and cluster velocities – can be precisely specified and thoroughly characterized using several diagnostic tools designed for Münster-type jet targets. These diagnostic tools allow for detailed optimization of the target conditions to meet the requirements of the respective experiment, e.g., for high precision experiments in nuclear and particle physics.
Advanced shadowgraphy measurements were employed to determine both the size and velocity distributions of the clusters. A commercial laser emitting a wavelength of 450 nm with a pulse duration of 129 ns is utilized, ensuring the clusters move during laser illumination. This allows not only to resolve the cluster size but also to extract key characteristics – including cluster diameter, velocity and flight direction – from the observed shadow patterns. The measured cluster size distribution is deconvolved using data acquired from a series of static particles with known sizes. This correction process addresses the dependence of the observed size on the distance from the objective-camera system’s focal plane.
These measurements were conducted across several different target stagnation conditions and nozzle designs to explore variations in cluster characteristics.
Additional beam diagnostic tools are positioned within the cluster-jet target’s beam dump, which efficiently re-moves clusters and residual gas not interacting with an accelerator beam. To optimize the beam dump perfor-mance, a dedicated setup was designed and commissioned with a newly implemented orifice system. A compre-hensive study was then conducted investigating vacuum pressure distributions along the target beam line and clus-ter-jet thicknesses under various stagnation conditions.
This presentation highlights key findings, including detailed characterization of individual clusters and their prop-erties. Furthermore, the optimization of high target thicknesses of more than $5\cdot10^{14}$ atoms/cm² at the interaction point which is 2.25 m downstream from the jet nozzle was carried out while maintaining minimal residual back-ground pressure through careful adjustment of the orifice system within the beam dump.
[1] S. Vestrick et al., EPJ Web Conf., 285 02002 (2023).
[2] P. Brand et al., Phys. Rev. Accel. Beams 29, 023001 (2026).
[3] H. Eick et al., Nucl. Instrum. Methods Phys. Res. A, 1085, 171245 (2026).