BEGIN:VCALENDAR VERSION:2.0 PRODID:-//linuxsoftware.nz//NONSGML Joyous v1.4//EN BEGIN:VEVENT SUMMARY:Direct laser acceleration of electrons: energy gain optimization a nd application to gamma-ray sources and pair plasmas DTSTART:20260316T140000Z DTEND:20260316T160000Z DTSTAMP:20261004T134412Z UID:927e97c0-e50e-43ff-887b-5a35694ce070 SEQUENCE:2 CREATED:20260310T142050Z DESCRIPTION:This thesis investigates direct laser acceleration (DLA) of el ectrons in underdense plasmas and demonstrates how to optimize the mechani sm to produce multi-GeV\, high-charge electron beams for applications such as gamma-ray generation\, neutron production\, and laboratory pair-plasma studies. In DLA\, electrons oscillate within a plasma channel while conti nuously interacting with the laser field\, enabling substantial energy tra nsfer and allowing hundreds of nanocoulombs of charge to reach relativisti c energies. The work combines analytical theory\, test-particle models\, a nd large-scale quasi-3D particle-in-cell simulations. The quasi-3D method makes multi-millimeter propagation tractable while retaining essential thr ee-dimensional physics\, allowing systematic scans of density\, spot size\ , and laser power. A key contribution is a new scaling law predicting the maximum electron energy attainable in DLA. The analysis shows that optimal acceleration occurs when electrons oscillate at a specific resonant displ acement from the channel axis\, maximizing sustained interaction with the laser’s transverse field. This leads to an optimal focusing condition th at ties laser power\, focal spot\, and plasma density together. Simulation s indicate that 10-PW lasers can drive electrons to ≈8 GeV with conversi on efficiencies of tens of percent. The thesis further extends DLA theory to smoothly varying plasma density profiles typical of experimental condit ions. A new approximate invariant is identified\, enabling prediction of t he maximum energy even when the density evolves. Density tailoring is show n to reduce acceleration length and mitigate radiation-reaction losses at extreme energies. Finally\, the work explores secondary radiation and part icle production. DLA electrons generate bright\, collimated gamma rays via betatron emission\, with analytically predicted critical energies matchin g simulations from 100-TW to 10-PW regimes. Two positron-generation pathwa ys are demonstrated: Bethe–Heitler production using high-Z targets and a simple single-laser scheme reaching the strong-field QED regime. Overall\ , the thesis establishes DLA as a powerful method for producing multi-GeV electrons\, brilliant gamma-ray beams\, and relativistic pair plasmas\, of fering a comprehensive framework for future multi-petawatt experiments LAST-MODIFIED:20260310T142126Z LOCATION:Anfiteatro PA3 (Piso -1 do Pavilhão de Matemática) do IST URL:http://df.vps.tecnico.ulisboa.pt/pt/eventos/direct-laser-acceleration- of-electrons-energy-gain-optimization-and-application-to-gamma-ray-sources -and-pair-plasmas/ X-ALT-DESC;FMTTYPE=text/html:

This thesis investi gates direct laser acceleration (DLA) of electrons in underdense plasmas a nd demonstrates how to optimize the mechanism to produce multi-GeV\, high- charge electron beams for applications such as gamma-ray generation\, neut ron production\, and laboratory pair-plasma studies. In DLA\, electrons os cillate within a plasma channel while continuously interacting with the la ser field\, enabling substantial energy transfer and allowing hundreds of nanocoulombs of charge to reach relativistic energies. The work combines a nalytical theory\, test-particle models\, and large-scale quasi-3D particl e-in-cell simulations.

The quasi-3D method makes multi-millimete r propagation tractable while retaining essential three-dimensional physic s\, allowing systematic scans of density\, spot size\, and laser power. A key contribution is a new scaling law predicting the maximum electron ener gy attainable in DLA. The analysis shows that optimal acceleration occurs when electrons oscillate at a specific resonant displacement from the chan nel axis\, maximizing sustained interaction with the laser’s transverse field.

This leads to an optimal focusing condition that ties las er power\, focal spot\, and plasma density together. Simulations indicate that 10-PW lasers can drive electrons to ≈8 GeV with conversion efficien cies of tens of percent. The thesis further extends DLA theory to smoothly varying plasma density profiles typical of experimental conditions. A new approximate invariant is identified\, enabling prediction of the maximum energy even when the density evolves. Density tailoring is shown to reduce acceleration length and mitigate radiation-reaction losses at extreme ene rgies.

Finally\, the work explores secondary radiation and parti cle production. DLA electrons generate bright\, collimated gamma rays via betatron emission\, with analytically predicted critical energies matching simulations from 100-TW to 10-PW regimes. Two positron-generation pathway s are demonstrated: Bethe–Heitler production using high-Z targets and a simple single-laser scheme reaching the strong-field QED regime. Overall\, the thesis establishes DLA as a powerful method for producing multi-GeV e lectrons\, brilliant gamma-ray beams\, and relativistic pair plasmas\, off ering a comprehensive framework for future multi-petawatt experiments

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