Radiation protection modelling for 2.5 Petawatt-laser production of ultrashort x-ray, proton and ion bunches: Monte Carlo model of the Munich CALA facility

Franz S Englbrecht,Peter G Thirolf,Andreas Döpp,Florian H Lindner,Jens Hartmann,Jörg Schreiber,Martin L Groß,Hans-F Wirth,George Dedes,Katia Parodi,Stefan Karsch

doi:10.1088/1361-6498/aba8e4

Abstract

The ‘Centre for Advanced Laser Applications’ (CALA) is a new research institute for laser-based acceleration of electron beams for brilliant x-ray generation, laser-driven sub-nanosecond bunches of protons and heavy ions for biomedical applications like imaging and tumour therapy as well as for nuclear and high-field physics.The radiation sources emerging from experiments using the up to 2.5 petawatt laser pulses with 25 femtosecond duration will be mixed particle-species of high intensity, high energy and pulsed, thus posing new challenges compared to conventional radiation protection. Such worldwide pioneering laser experiments result in source characteristics that require careful a-priori radiation safety simulations.The FLUKA Monte-Carlo code was used to model the five CALA experimental caves, including the corridors, halls and air spaces surrounding the caves. Beams of electrons (), protons (), 12C () and 197Au () ions were simulated using spectra, divergences and bunch-charges based on expectations from recent scientific progress.Simulated dose rates locally can exceed 1.5 kSv h−1 inside beam dumps. Vacuum pipes in the cave walls for laser transport and extraction channels for the generated x-rays result in small dose leakage to neighboring areas. Secondary neutrons contribute to most of the prompt dose rate outside caves into which the beam is delivered. This secondary radiation component causes non-negligible dose rates to occur behind walls to which large fluences of secondary particles are directed.By employing adequate beam dumps matched to beam-divergence, magnets, passive shielding and laser pulse repetition limits, average dose rates in- and outside the experimental building stay below design specifications () for unclassified areas, for supervised areas, maximum local dose rate) and regulatory limits ( for unclassified areas).

Highlights

We report here the results of Monte Carlo simulations of different source types relevant to various Centre for Advanced Laser Applications’ (CALA) experiments, in terms of calculated dose rates, with respect to established dose limits
The peak dose rate occurred, for each cave, in the respective beam dump, but dose rates higher than 10 μSv h−1 were present in large sections of each cave during operation of the laser
For the experiments producing protons and heavier ions (LION and HF), the dose rate is listed as an electron beam component and the respective proton or heavy ion beam component

Summary

Introduction

Since the theoretical prediction of electron acceleration driven by high peak power femtosecond lasers in 1979, the development of techniques to increase the peak power of lasers, led to the development of femtosecond ( fs) short petawatt ( PW) class lasers for particle acceleration [1, 2].The ‘Centre for Advanced Laser Applications’ (CALA) in Garching, near Munich (Germany) is intended for laser-based acceleration of electron beams for brilliant x-ray generation (’Laser-driven Undulator x-ray Source’ beamline (LUX), ‘Electron and Thomson Test Facility’ beamline (ETTF), ‘Source for Powerful Energetic Compact Thomson Radiation Experiments’ beamline (SPECTRE)) and laser-driven nanosecond bunches of protons and heavy ions (‘Laser-driven Ion Acceleration’ beamline (LION), ‘High Field’ beamline (HF)) for the investigation of the laser-acceleration and application of energetic protons and ions.Laser-accelerated ion bunches have been proposed for use in radiation therapy of cancer [3]. The ‘Centre for Advanced Laser Applications’ (CALA) in Garching, near Munich (Germany) is intended for laser-based acceleration of electron beams for brilliant x-ray generation (’Laser-driven Undulator x-ray Source’ beamline (LUX), ‘Electron and Thomson Test Facility’ beamline (ETTF), ‘Source for Powerful Energetic Compact Thomson Radiation Experiments’ beamline (SPECTRE)) and laser-driven nanosecond bunches of protons and heavy ions (‘Laser-driven Ion Acceleration’ beamline (LION), ‘High Field’ beamline (HF)) for the investigation of the laser-acceleration and application of energetic protons and ions. Albeit the source characteristics of laser-accelerated ion bunches differ significantly from those of conventional sources, the former can be utilised in a wide range of novel biomedical applications and offer distinct advantages: reasonable compactness and cost effectiveness, synchronisation to laser pulses at a picosecond level, simple target and particle species changeability, broad energy spectrum, small source size, down to nanosecond bunch duration, allowing to use new bunch detection techniques and to study ultrashort biological effects [4,5,6,7]. Based on electron bunches accelerated in a plasma, these sources can be tailored to have the necessary properties of being compact and of delivering collimated, incoherent, and femtosecond pulses of x-ray radiation [5, 10, 11]

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Conclusion