Fully characterised and online monitored beamline for high-dose-rate laser-proton irradiation experiments at Draco PW

Laser-driven proton pulse provide unique properties in terms of pulse structure (ns) and instantaneous dose rate (10^9 Gy/s) but - inherently broadband and highly divergent - pose a challenge to established beamline concepts on the path to application-adapted irradiation field formation, particularly for three-dimensional cases. We present the successful implementation and characterisation of a highly efficient and tuneable dual pulsed solenoid beamline at the Draco PW facility[1] to generate volumetric dose distribution tailored to specific applications[2]. The vast experimental scope and already successfully performed studies range from systematic volumetric in-vivo tumour irradiations in a dedicated mouse model (with a stable mean dose delivery of ±10 % and a spatial dose homogeneity of ±5 % over a cylindrical volume of 5 mm diameter and height) to high-dose-rate irradiations in the FLASH regime (using proton peak dose rates of up to 10^9 Gy/s with about 20 Gy/shot homogeneously over a cylindrical sample volume of 4.5 mm diameter and 3 mm height) as well as particle diagnostics commissioning (with a multitude of spatial and spectral dose distributions). The beamline setup is complemented by a complex beam monitoring and dosimetry detector suite adapted to the ultra-high dose rate pulses and is in its unique synergy and redundancy capable of %-level precision dose delivery to samples as required for systematic irradiation studies. In addition to established radiochromic film dosimetry, the detector suite includes saturation-corrected (transmission) ionisation chambers [3] as well as screen and bulk scintillator setups, partly with tomographic reconstruction capabilities for 3D dose distribution retrieval. Moreover, non-invasive, single-shot-capable online time-of-flight-based spectral characterisation of filtered proton pulses has proven a powerful tool for beam monitoring as well as dosimetric purposes. In this presentation the complex and versatile dose delivery system of laser-driven protons at the Draco PW using pulsed solenoids will be discussed. Its characterisation, technological development and improvement as well as the dosimetry suite as a vital part of the precise dose delivery will be addressed, while the presentation by U. Schramm covers recent experimental activities in detail. [1] T. Ziegler, et al., Proton beam quality enhancement by spectral phase control of a PW-class laser system, https://arxiv.org/abs/2007.11499 (2020) [2] Brack, et al., Spectral and spatial shaping of laser-driven proton beams using a pulsed high-field magnet beamline, SciRep, 10:9118, (2020) [3] Gotz M, et al., A new model for volume recombination in plane‐parallel chambers in pulsed fields of high dose‐per‐pulse. Phys Med Biol., 62: 8634, (2017)