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Formation of Ultrarelativistic Electron Rings from a Laser-Wakefield Accelerator.
B B Pollock1, F S Tsung2, F Albert1
1Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA.
Physical Review Letters
|August 15, 2015
Summary
Ultrarelativistic electron rings were observed in laser-wakefield acceleration. These structures form from trapped electrons in a hollow pocket, propagating in free space and potentially accelerating positrons.
Area of Science:
- Plasma Physics
- Particle Acceleration
Background:
- Laser-wakefield acceleration (LWFA) experiments in the blowout regime have observed ultrarelativistic electron ring structures.
- These rings exhibit energies of 170-280 MeV, energy spreads of 5%-25%, and charges around 10 pC across various plasma conditions.
Purpose of the Study:
- To investigate the formation mechanism of ultrarelativistic electron rings observed in LWFA.
- To understand the role of laser intensity enhancement and wake structure in electron trapping and ring formation.
Main Methods:
- Utilizing three-dimensional particle-in-cell (PIC) simulations to model the laser-plasma interaction.
- Analyzing electron density distributions and particle dynamics within the laser wake.
Main Results:
- Simulations reveal laser intensity enhancement leading to sheath splitting and a hollow toroidal electron density pocket behind the first wake period.
- Electrons dephasing beyond the ideal dephasing length can become trapped in this pocket, forming ultrarelativistic rings.
- These rings propagate in free space for meter-scale distances after exiting the plasma.
Conclusions:
- The formation mechanism of ultrarelativistic electron rings is elucidated through PIC simulations.
- The observed electron rings act as relativistic potential wells, indicating potential applications for accelerating positrons.
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