Charged particle beam transport in a flying focus pulse with orbital angular momentum

TL;DR

This paper demonstrates that Flying Focus laser pulses with orbital angular momentum can effectively confine ultra-relativistic charged particle bunches over long distances using lower energy pulses, with enhanced stability from radiative cooling.

Contribution

It introduces a novel method of particle confinement using FF pulses with OAM, achieving stable transport at lower energies than traditional methods.

Findings

FF pulses with OAM create a radial ponderomotive barrier.

Particles co-travel with the barrier, oscillating around the axis.

Radiative cooling reduces bunch radius and emittance during propagation.

Abstract

We demonstrate the capability of Flying Focus (FF) laser pulses with $\ell = 1$ orbital angular momentum (OAM) to transversely confine ultra-relativistic charged particle bunches over macroscopic distances while maintaining a tight bunch radius. A FF pulse with $\ell = 1$ OAM creates a radial ponderomotive barrier that constrains the transverse motion of particles and travels with the bunch over extended distances. As compared to freely propagating bunches, which quickly diverge due to their initial momentum spread, the particles co-traveling with the ponderomotive barrier slowly oscillate around the laser pulse axis within the spot size of the pulse. This can be achieved at FF pulse energies that are orders of magnitude lower than required by Gaussian or Bessel pulses with OAM. The ponderomotive trapping is further enhanced by radiative cooling of the bunch resulting from rapid oscillations of the charged particles in the laser field. This cooling decreases the mean square radius and emittance of the bunch during propagation.