Magnetically collimated relativistic charge-neutral electron–positron beams from high-power lasers

Abstract

We report the observation of charge-neutral MeV electron–positron beams from magnetically collimated laser-driven pair-production experiments. Relativistic pairs of electrons were generated from laser–solid interactions in an external 13-T mirror field. The pairs were subsequently confined, deflected, or collimated depending on the particle energy and field strength and measured by a magnetic particle spectrometer. Equal quantities of positrons and electrons were measured in the collimated beams with an energy around 13 MeV along the magnetic mirror axis.

Confinement of relativistic electrons in a magnetic mirror en route to a magnetized relativistic pair plasma

“…The energy of the broad peaks in the axial spectrum corresponds to the electron energy, for which the focal length is the coil-to-target distance 7.5 mm, i.e., the energy of electrons that should be collimated. 51 The narrower spikes in the measured axial loss spectra below 5 MeV have been noted in magnetic focusing experiments 41 and correspond to complicated trajectories of specific energy electrons, which focus and subsequently re-collimate upon exiting the coil. There is significant variation in the spectra between shots; this may be related to variation in the laser parameters, tilt off the mirror axis (3 -5 ) in the construction of the coils, 51 and shot-to-shot variation in the magnitude of the magnetic field.…”

“…51 The narrower spikes in the measured axial loss spectra below 5 MeV have been noted in magnetic focusing experiments 41 and correspond to complicated trajectories of specific energy electrons, which focus and subsequently re-collimate upon exiting the coil. There is significant variation in the spectra between shots; this may be related to variation in the laser parameters, tilt off the mirror axis (3 -5 ) in the construction of the coils, 51 and shot-to-shot variation in the magnitude of the magnetic field. The radial spectra have a strong dependence on the magnetic field magnitude because of the large azimuthal rotation introduced by the field.…”

“…The pairs could then be magnetically transported to the mirror with a solenoid acting as collimating lens. The lens would select particle energy, and if tilted also select charge, 51 so that a unity charge ratio pair beam could be injected into the mirror. A thin foil placed inside the mirror could scatter the injected pairs out of the loss cone.…”

Ion Acoustic Shock Wave Formation and Ion Acceleration in the Interactions of Pair Jets with Electron–ion Plasmas

“…This study may help us understand some related astrophysical processes, such as the fireball model of GRBs, the shock model of PWN, and the origin of high-energy cosmic rays (Drury 2012;Blasi 2013). With the advances in high-intensity laser technology, it has become possible to generate high-energy (MeV) charge-neutral e − e + pair plasmas in the laboratory (Sarri et al 2015;Chen et al 2015;Liang et al 2015;Warwick et al 2017;Jiang et al 2021;Peebles et al 2021). Thus, our scheme will be attractive for experimental studies, which may open new opportunities for…”

Collimation, compression and acceleration of isotropic hot positrons by an intense vortex laser

“…Due to broad energy spectrum of positron beams, temporal lengthening and density decreasing occur, since positrons of different energy have different focal lengths in axial magnetic fields and different flight times after leaving the external fields. Peebles et al [28] used magnetic mirror fields along the normal direction of the target axes to choose and collimate positrons of roughly 13 MeV over a long distance (>50 cm), while positrons with higher or lower energy were significantly deflected and defocused. Audet et al [10] placed a compact beam-line, consisting of two Hallbach quadrupole magnets, two collimators and two dipole magnets, after targets for energy-collection and collimation of laser-driven positron beams.…”