Laser wakefield acceleration at reduced density in the self-guided regime

Abstract

Experiments conducted using a 200TW 60 fs laser have demonstrated up to 720 MeV electrons in the self-guided laser wakefield regime using pure Helium gas jet targets. Charge and energy of the accelerated electrons was measured using an electron spectrometer with a 0.5T magnet and charge callibrated image plates. The self-trapped charge in a helium plasma was shown to fall off with decreasing electron density with a threshold at 2.5 × 10 18 (cm −3 ) below which no charge is trapped. Self-guiding however is shown to continue below this density limitation over distances of 14 mm with an exit spot size of 25µm. Simulations show that injection of electrons at these densities can be assisted through ionization induced trapping in a mix of Helium with 3% Oxygen.

Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime

“…18, 27 Experiments also demonstrate that even in high-density plasmas, such as c g < 25, bubble formation alone is not sufficient for self-injection and production of high-energy electrons. 13,14,19,20 Therefore, understanding the self-injection process and its relation to nonlinear relativistic optical dynamics of the driver is vital for the production of high-quality beams.…”

“…They rapidly equalize in energy with earlier injected particles, and a monoenergetic bunch forms long before dephasing. 24,26,27 Secondary injection into the same bucket (dark current) remains suppressed, and low-energy tails [12][13][14]28,29 do not develop in the electron spectra.…”

“…[11][12][13][14][15] Both numerical modeling 3,[16][17][18] and direct experimental diagnostics 19,20 show close correlation between generation of collimated, quasi-monoenergetic electron beams and formation of a unique plasma structureelectron density "bubble"-trailing in the wake of a tightly focused ultraintense laser pulse (I peak > 10 19 W=cm 2 ). The laser ponderomotive force creates full electron cavitation behind the driver, while fully stripped ions remain immobile.…”

Energy Spread Reduction of Electron Beams Produced via Laser Wake

“…Electron spectra from each of the three gas jet targets have been recorded for electron densities ranging from 3x10 18 cm −3 to 9x10 18 cm −3 [14,36]. The maximum electron beam energy recorded during these experiments is 720 MeV, which corresponds to an electron density of 3x10 18 cm −3 using the 8 mm gas jet.…”

Optically Controlled Laser-Plasma Electron Acceleration for Compact γ-Ray Sources

“…Yet this process, apart from limiting the energy gain, destroys e-beam most assuredly if acceleration extends through the pulse depletion. (A plethora of evidence exists to this effect, both in laboratory experiments and numerical simulations [16,19,[22][23][24][25][38][39][40][41][42].) To enable a new generation of compact particle and radiation sources [43,44], one has to bypass the limitations this of scaling by designing an optical driver resilient to self-phase-modulation and self-compression.…”