Laser-driven particle acceleration is based on the interaction of ultra-intense ultrashort laser pulses with matter and therefore requires rapidly renewable, high-purity target systems capable of stable operation at kHz repetition rates [1]. Among currently available solutions, liquid jets represent a suitable approach due to their unique combination of fast target refreshment and excellent shot-to-shot reproducibility [2]. In particular, cryogenic liquid jets provide a continuous and debris-free source of accelerated particles and radiation, which is essential for maintaining secondary beam quality and compatibility with sensitive optical components [3]. Their high purity also makes these targets highly advantageous for numerical simulations.
 
The cryogenic target platform developed at the ELI Beamlines Cryogenic Laboratory is intended to support kHz laser operation. It is based on a helium-free closed-cycle cryocooler combined with a custom-designed condensation cell capable of reaching temperatures as low as 4 K. A cold head placed inside a helium exchange gas volume ensures low-vibration and efficient thermal coupling to a cold plate, which in turn supports a brass or cooper condensation cell. The cell features an exchangeable nozzle with apertures from 5 to 25 μm, determining the liquid jet diameter. This configuration enables long-term and stable extrusion of high-purity reproducible cryoliquid flow.
 
Cryojets of nitrogen, argon, and krypton have already been obtained. Current efforts focus on optimizing the target performance. For instance, the stable 10 μm nitrogen column jet with adjustable velocity of 5–20 m/s was achieved at 70 K and 0.5 - 7 bar, while a chamber pressure 10??–10?³ mbar remains suitable for laser driven ion acceleration. Ongoing work focuses on expanding the range of liquefied gases [4] and minimizing jet spatial fluctuations.
 
[1] Ionescu SC, Phung VLJ, Gheorghiu C, et al. Short overview of solid, gas, cryogenic, and liquid targets fabrication for single beam high power laser experiments. High Power Laser Science and Engineering. Published online 2026:1-20. doi:10.1017/hpl.2026.10132
[2] Nina Gamaiunova, Maksym Tryus, Filip Grepl, Andriy Velyhan, Stanislav Stancek, Vasiliki Kantarelou, G. A. Pablo Cirrone, Daniele Margarone, Lorenzo Giuffrida, Timofej Chagovets, "Liquid jet target system for laser-plasma interactions at kHz repetition rate," Proc. SPIE 12579, Laser Acceleration of Electrons, Protons, and Ions VII, 1257908 (8 June 2023); https://doi.org/10.1117/12.2665607
[3] Chagovets T, Viswanathan J, Tryus M, Grepl F, Velyhan A, Stancek S, Giuffrida L, Schillaci F, Cupal J, Koubikova L, Garcia D, Manzagol J, Bonnay P, Souris F, Chatain D, Girard A and Margarone D (2022) A Cryogenic Hydrogen Ribbon for Laser Driven Proton Acceleration at Hz-Level Repetition Rate. Front. Phys. 9:754423. doi: 10.3389/fphy.2021.754423
[4] Timofej Chagovets; Hydrogen targetry in laser-plasma physics. Low Temp. Phys. 1 August 2022; 48 (8): 645–650. https://doi.org/10.1063/10.0012652

Keywords
Cryogenic targetry|Cryoliquid microjet