Paper | Title | Page |
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MOP081 | Proton Acceleration by Trapping in a Relativistic Laser Driven Uphill Plasma Snowplow | 247 |
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We explore a novel regime of proton and ion acceleration off of overdense Plasma created by a Laser pulse. In Coulomb explosion, Target Normal Sheath, Acoustic shock acceleration regimes the protons are neither high-energy nor monoenergetic enough for applications such as hadron radiation therapy, fast ignition fusion research and particle physics. This calls out for exploration of effective regimes of acceleration. The proposed Snowplow regime of acceleration uses a Snowplow of charge created by a relativistic Laser pulse at the critical density on a uphill Plasma density gradient. The relativistically moving Snowplow's space charge drags the protons and its velocity can be controlled to effectively trap the protons using laser pulse shape and the uphill density profile. We describe the principles behind this mechanism. We derive analytical expressions for the Snowplow velocity and its dependence on the parameter space. We primarily explore the density gradient and laser pulse shape to optimally accelerate protons from rest to the desired velocities. Preliminary, 1-D simulation results are presented and analyzed. | ||
MOP143 | Enhanced Laser-Driven Ion Acceleration via Forward Raman Scattering in a Ramped Gas Target | 358 |
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Funding: This work is supported by DOE grant DE-FG02-92ER40727. CO2 laser-plasma interactions provide a unique parameter space for using a gas jet for Target Normal Sheath Acceleration (TNSA) of ions instead of a thin foil target. The generation of 1-5 MeV protons from the interaction of a 3 ps TW CO2 laser pulse with a gas target with a peak density around the critical plasma density (1019 cm-3) has been studied by 2D particle-in-cell simulations. The proton acceleration in the preformed plasma, having similar to the gas jet symmetric, linearly ramped density distribution, occurs via formation of a sheath of hot electrons on the back surface of the target. The maximum energy of the hot electrons and, hence net acceleration of protons is mainly defined by Forward Raman scattering instability in the underdense part of the plasma. This mechanism of an additional heating of electrons is strongly affected by nonlinear laser-plasma interactions and results in the proton energy enhancement by more than an order of magnitude in comparison with the regular ponderomotive force scaling of TNSA. Forward directed ion beams from a gaseous target can find an application as a high-brightness ion source-injector. |
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