We present experimental studies of a laser-driven open-geometry platform for energy-selective tailoring of laser-accelerated particle beams. A high intensity sub ps-laser pulse drives target-discharge and subsequent propagation of strong transient electromagnetic (EM) fields guided by the target geometry.
Proton-deflectograms capture the time- and spatial-scales: the discharge pulse with a FWHM of ≈ 40 ps propagates with a phase speed of (0.82 ± 0.06) • c, emanating from the laser-plasma interaction spot. While streaming around a coil shaped feature in the target rod, the EM fields efficiently focus the probing protons passing inside the coil: e.g. the emittance of 6.3 MeV protons shrinks to 30 % of the initial value. We perform energy-selection of the best focused particles by tuning the delay between the laser pulses driving the discharge and accelerating the proton beam.
Synthetic counterparts of the proton imprints are obtained from simulations of test-particle transport and EM-mode propagation using the PAFIN code. We find EM-pulse amplitudes of tens of GV/m and tens of Tesla. Detailed PIC simulations of the laser-target interaction and the successive propagation of the EM-waves along the target agree in field strength and allow to distinguish between fast electron currents, EM pulses and neutralization waves.
Building upon this, we intend to present a first predictive modeling of the discharge pulse depending on target geometry and material, and laser driven discharge.
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