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Abstract Using plasma mirror injection we demonstrate, both analytically and numerically, that a circularly polarized helical laser pulse can accelerate highly collimated dense bunches of electrons to several hundred MeV using currently available laser systems. The circular-polarized helical (Laguerre–Gaussian) beam has a unique field structure where the transverse fields have helix-like wave-fronts which tend to zero on-axis where, at focus, there are large on-axis longitudinal magnetic and electric fields. The acceleration of electrons by this type of laser pulse is analyzed as a function of radial mode number and it is shown that the radial mode number has a profound effect on electron acceleration close to the laser axis. Using three-dimensional particle-in-cell simulations a circular-polarized helical laser beam with power of 0.6 PW is shown to produce several dense attosecond bunches. The bunch nearest the peak of the laser envelope has an energy of 0.47 GeV with spread as narrow as 10%, a charge of 26 pC with duration of ∼ 400 as, and a very low divergence of 20 mrad. The confinement by longitudinal magnetic fields in the near-axis region allows the longitudinal electric fields to accelerate the electrons over a long period after the initial reflection. Both the longitudinal E and B fields are shown to be essential for electron acceleration in this scheme. This opens up new paths toward attosecond electron beams, or attosecond radiation, at many laser facilities around the world.
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Realizing laminar-like flow in charged bunches with density evolution equations
In the ultra-fast electron microscopy community, electron bunches with much smaller longitudinal widths than transverse widths are emitted from the cathode surface. The community has believed that these bunches evolve to a uniform ellipsoid, but recent simulations by our group and others suggest that if the bunch has an initially transverse Gaussian profile, a ring-like density “shock” emerges at the median of the bunch during evolution. To explain these results, we generalized Reed’s 1D fluid model of charged bunch expansion to cylindrical and spherical geometries demonstrating such a shock emerges analytically under these symmetric geometries. Mathematically, the shock in these models occurs when particles more toward the middle “catch-up” to outer particles, and eventually the trajectory of the more central particle crosses-over the outer particle’s trajectory. This cross-over marks the transition from the laminar to nonlaminar regime. However, this theory has been developed for cold-bunches, i.e. bunches of electrons with zero initial momentum. Here, we briefly review this new theory and extend it to the cylindrically- and spherically-symmetric cases that have nonzero initial momentum. This formulation elucidates how charge-dominated bunches may be manipulated to maintain laminar conditions even through focussing of the bunch.
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- Award ID(s):
- 1803719
- PAR ID:
- 10164442
- Date Published:
- Journal Name:
- International Journal of Modern Physics A
- Volume:
- 34
- Issue:
- 36
- ISSN:
- 0217-751X
- Page Range / eLocation ID:
- 1942042
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1142/S0217751X19420429
