We demonstrate the capability of flying focus (FF) laser pulses with ℓ=1 orbital angular momentum (OAM) to transversely confine ultrarelativistic charged particle bunches over macroscopic distances while maintaining a tight bunch radius. A FF pulse with ℓ=1 OAM creates a radial ponderomotive barrier that constrains the transverse motion of particles and travels with the bunch over extended distances. As compared with freely propagating bunches, which quickly diverge due to their initial momentum spread, the particles cotraveling 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.

ELI Beamlines Facility The Extreme Light Infrastructure ERIC 252 41 Dolní Břežany Czech Republic

GOLP Instituto de Plasma e Fusão Nuclear Instituto Superior Técnico Universidade de Lisboa 1049 001 Lisbon Portugal

Laboratory for Laser Energetics University of Rochester Rochester New York 14623 USA

Max Planck Institute for Nuclear Physics Saupfercheckweg 1 D 69117 Heidelberg Germany

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