Experimental techniques for measurement of ultra-high-intensity laser generated gamma rays at ELI Beamlines

Production of intense and energetic gamma-ray sources in dense laser-irradiated plasmas is of fundamental interest in many fields of science (two-photon pair production, medical isotope production, nuclear waste analysis, etc.). One of the techniques to generate such photons is the interaction of an ultra-high-intensity laser pulse with low-mass foam targets. In these conditions, where the electron density is close to the plasma critical density, very strong magnetic fields (multi-GG) are generated. These magnetic fields enhance electron acceleration inside the plasma, which consequently, emit gamma rays from tens to hundreds of MeV. The currently available L3 high-repetition rate PW-class laser (30J, 30fs, 10Hz) at ELI Beamlines fulfills the requirements for such research.

However, an important work must be made regarding diagnostics for being able to operate such experiments at decent repetition rates. Indeed, standard gamma-ray diagnostics use passive detectors to record the signal, which are not suitable for high-repetition rate operation at ELI Beamlines. Here, we describe the design and the challenging implementation of an active gamma-ray calorimeter in extreme environments (i.e. electromagnetic pulses, particles and ultra high-vacuum).