Generation of intense quasi-electrostatic fields due to deposition of particles accelerated by petawatt-range laser-matter interactions

Abstract

We demonstrate here for the first time that charge emitted by laser-target interactions at petawatt peak-powers can be efficiently deposited on a capacitor-collector structure far away from the target and lead to the rapid (tens of nanoseconds) generation of large quasi-static electric fields over wide (tens-of-centimeters scale-length) regions, with intensities much higher than common ElectroMagnetic Pulses (EMPs) generated by the same experiment in the same position. A good agreement was obtained between measurements from a classical field-probe and calculations based on particle-flux measurements from a Thomson spectrometer. Proof-of-principle particle-in-cell simulations reproduced the measurements of field evolution in time, giving a useful insight into the charging process, generation and distribution of fields. The understanding of this charging phenomenon and of the related intense fields, which can reach the MV/m order and in specific configurations might also exceed it, is very important for present and future facilities studying laser-plasma-acceleration and inertial-confinement-fusion, but also for application to the conditioning of accelerated charged-particles, the generation of intense electric and magnetic fields and many other multidisciplinary high-power laser-driven processes.

Laser produced electromagnetic pulses: generation, detection and mitigation

“…The rise of the electric field depends on the shot and for the thinnest target (shot #16) occurs earlier with respect to the others, as expected for more energetic protons. These considerations are confirmed by the spectrum of protons detected by the TS1 spectrometer in the backward direction for the shots #16 and #29 [73] .…”

“…Figure 13 shows a comparison of the normalized D-dot measurements and simulation results for shot #29 at the same position, for both x and u (the sensitive D-dot axis normal to its ground plane) components of the electric field. Even with this rather simple model, a close agreement is reached, and the optimized proton energy range is in good correspondence with the most energetic part of spectrum measured by TS1 [73] .…”

“…This was demonstrated for energetic petawatt-range lasermatter interactions [73] using the Vulcan Petawatt laser at the Rutherford Appleton Laboratory (RAL), operating at a wavelength of 1054 nm [74] . Pulses of ∼1 ps duration were focused by an off-axis parabolic mirror at an intensity above 10 20 W • cm −2 on parylene-N foil targets at normal incidence.…”

“…The electromagnetic contribution is capable of generating photoionization on any exposed surface, and can thus create a layer of emitted electrons with energies of a few eV surrounding it and leave a transient superficial positive charge. On a slightly longer timescale, MeV-range relativistic electrons are expected to deposit a negative charge on the same surfaces, since secondary-electron emission at those energies is smaller than unity [73] . These two processes operate in opposite directions, and it is not trivial to estimate the electric fields due to their superimposition.…”

“…In order to recover the original s 2 (t) signal obtained by the EMP probe from the stored s 3 (t), an accurate knowledge of h TL (t) or alternatively of its Fourier transform H TL ( f ) = F{h TL (t)}( f ) is required, F being the Fourier transform operator. The second approach is usually preferred [73] , and from this it is possible to obtain…”