Speaker
Michael Ehret
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.2026.pdf
Transient Electromagnetic Fields for High Energy-Density Beam
Tailoring Driven by ps-Laser Pulses
M. Ehret 1,2, J. Alpiñaniz 3, V. Bagnoud 4, M. Bailly-Grandvaux 1, C. Brabetz 4,
E. d’Humières 1, Ph. Korneev 5, S. Malko 3, C. Matveevskii 5, A. Morace 6, L. Volpe 3,
M. Roth 2, G. Schaumann 2, V.T. Tikhonchuk 1, and J.J. Santos 1
1
Université de Bordeaux, CNRS, CEA, CELIA (Centre Lasers Intenses et Applications),
UMR 5107, Talence, France
2
Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany
3
Centro de Láseres Pulsados, Salamanca, Spain
4
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany
5
National Research Nuclear University MEPhI, Moscow, Russian Federation
6
Institute of Laser Engineering, Osaka University, Osaka, Japan
We present experimental studies of an open-geometry platform for energy selective
tailoring of laser-accelerated particle beams, with reference to different target geometries
and optimization prospects. The presented results are supported by theoretical analysis
based on PIC simulations and modelling. In the all-optical principle, a high intensity ps-
laser pulse drives electromagnetic (EM) target-discharge and subsequent propagation of
strong transient EM-fields guided by the target geometry. A sub-mm coil-shaped part of the
target rod creates lensing effects that arise due to magnetic- and electric-contributions, in
particular we imaged energy-selective proton beam focusing over cm-scale distances by
proton-deflectometry and we showed the clear evidence of a some Tesla strong magnetic
field component based on its polarity.
The experiment was carried out at the PHELIX/GSI laser facility, using 500 fs, 50 J laser
pulses focused at 5·1018 W/cm2 into a flat-disc target conductively connected to a 50 µm-
thick wire shaped as a coil of 500 µm diameter. The discharge time and spatial scales were
captured by proton-deflectometry (Figure 1), revealing the propagation of transient EM-
fields emanating from the laser-plasma interaction. The measured phase speed through the
target rod is (0.95 ± 0.05) c. The discharges stream around the coil over ≈ 25 ps, producing
efficient focusing of the protons passing inside the coil: 12 MeV-protons are collimated
over distances of several cm. In Fig. 1, the emittance of 6 MeV protons shrinks to 30% of
the initial value. Energy-selection for the focused particles is possible by tuning the delay
between the laser pulse driving the coil and the one accelerating the proton beam.
Analysis with transport- and field-simulations using the PAFIN code [DOI: 10.13140 /
RG.2.1.3855.7847] assuming a dynamic EM-discharge pulse streaming along the target
capture the discharge dynamics with amplitudes of tens of GV/m and tens of T. Detailed
PIC simulations of the laser-target interaction and the successive propagation of the EM-
waves streaming along the target and propagating in the free space around the target agree
in field strength and point us to different electromagnetic effects difficult to separate: the
propagation of fast electrons, EMP and neutralization wave.
Figure 1: Experimental data in the top row, PAFIN simulation results in the bottom row.
