Design of modular multi-channel electron spectrometers for application in laser matter interaction experiments at Prague Asterix Laser System

Abstract

This paper describes design, development, and implementation of a multi-channel magnetic electron spectrometer for the application in laser–plasma interaction experiments carried out at the Prague Asterix Laser System. Modular design of the spectrometer allows the setup in variable configurations to evaluate the angular distribution of hot electron emission. The angular array configuration of the electron spectrometers consists of 16 channels mounted around the target. The modules incorporate a plastic electron collimator designed to suppress the secondary radiation by absorbing the wide angle scattered electrons and photons inside the collimator. The compact model of the spectrometer measures electron energies in the range from 50 keV to 1.5MeV using ferrite magnets and from 250 keV to 5MeV using stronger neodymium magnets. An extended model of the spectrometer increases the measured energy range up to 21MeV or 35MeV using ferrite or neodymium magnets, respectively. Position to energy calibration was obtained using the particle tracking simulations. The experimental results show the measured angularly resolved electron energy distribution functions from interaction with solid targets. The angular distribution of hot electron temperature, the total flux, and the maximum electron energy show a directional dependence. The measured values of these quantities increase toward the target normal. For a copper target, the average amount of measured electron flux is 1.36 × 1011, which corresponds to the total charge of about 21 nC.

Experimental tests and signal unfolding of a scintillator calorimeter for laser-plasma characterization

“…The unfolded MB temperature of the photons is (60.6±2.6) keV, the R-squared is 0.999, and p-value is 10 −10 . The result is in the same range as the hot electrons temperatures (50-100 keV) estimated by electron spectrometers used in the previous experiments at PALS under similar experimental conditions [51,52], which is in accordance with the expectations.…”

Influence of the magnetic field on properties of hot electron emission from ablative plasma produced at laser irradiation of a disc-coil target

“…• Three-frame complex interferometry measuring the spacetime electron density and the SMF distributions in the expanded plasma [22,23], • Four-frame x-ray pinhole camera visualizing the expansion plasma process in the range of the soft x-ray radiation [25], • 2D imaging of the Cu Kα line emission [27] providing information on parameters of the HE emission, namely the total number of photons generated as a result of the interaction of HEs with a copper disc, the energy and laser-to-HE conversion efficiency for HEs deposited in the central hot spot of the targets, the fraction of the HEs deposited outside the central hot spot and • the multi-channel electron magnetic spectrometer [26] measuring the angular characteristics of the HEs emitted outside the Cu discs, i.e. the number of HEs emitted at different angles vs the target normal and angular distributions of their energy and temperature.…”

“…The characteristics of HEs emitted from the interaction region outside the target surface were investigated using a multi-channel magnetic electron spectrometer [26] schematically shown in figure 9 where the configuration of individual modules is depicted. The typical measured data processed using the known characteristics of the spectrometer are presented in figure 10.…”

“…Plasma expands in the axial magnetic field generated by the current flowing in the DC circuit. To investigate the influence of the magnetic field on the parameters of the expanded plasma, the three-frame complex interferometry [22][23][24] and four-frame x-ray camera [25] were implemented in combination with measurements of the HE energy distributions using the multi-channel magnetic spectrometer [26] and 2D imaging of the Cu Kα line emission [27].…”

Online measurements of gamma radiation from laser-plasma and signal unfolding using a scintillator calorimeter

“…According to the electron spectrometer data that was used during the previous PALS experiments performed under similar experimental conditions 30,31 , electron temperatures usually fell within the (80 -150) keV range. Assuming that the Bremsstrahlung temperature should be similar or less than that of the electrons, our findings are in accordance with the expectations.…”