High-quality stable electron beams from laser wakefield acceleration in high density plasma

High-quality, stable electron beams are produced from self-injected laser wakefield acceleration using the interaction of moderate 3 TW, 45 fs duration Ti:sapphire laser pulses with high density ($>5\times {10}^{19}{\mathrm{cm}}^{-3}$) helium gas jet plasma. The electron beam has virtually background-free quasimonoenergetic distribution with energy ${35.6}_{-2.5}^{+3.9}\mathrm{MeV}$, charge ${3.8}_{-1.2}^{+2.8}\mathrm{pC}$, divergence and pointing variation $\sim 10\mathrm{mrad}$. The stable and high quality of the electron beam opens an easy way for applications of the laser wakefield accelerator in the future, particularly due to the widespread availability of sub-10 TW class lasers with a number of laser plasma laboratories around the world.

Figure 1

A schematic diagram of the experimental setup.

Figure 2

Images of the electron beam on the DRZ phosphor screen for varying plasma density: (a) $5.8\times {10}^{19}{\mathrm{cm}}^{-3}$, (b) $6.8\times {10}^{19}{\mathrm{cm}}^{-3}$, and (c) $8.6\times {10}^{19}{\mathrm{cm}}^{-3}$. The images show well-defined profiles with no background halo, particularly at lower density. The FWHM divergences of the electron beam in the horizontal direction are 13 mrad, 26 mrad, and 33 mrad for the images (a), (b), and (c), respectively.

Figure 3

Images of energy dispersed electron beams (on the phosphor) produced in 15 consecutive laser shots, at an electron density of $\sim 5.8\times {10}^{19}{\mathrm{cm}}^{-3}$ in helium plasma. The color scale is normalized for each shot.

Figure 4

A lineout energy spectrum of a typical electron beam at an electron density of $\sim 5.8\times {10}^{19}{\mathrm{cm}}^{-3}$ in helium plasma, showing almost no low-energy background. The horizontal line on top of the peak shows the uncertainty in the peak energy due to pointing variation within the 8 mrad acceptance angle of the electron spectrograph.

Figure 5

A histogram of the peak energy of the quasimonoenergetic electron beams produced at an electron density of $\sim 5.8\times {10}^{19}{\mathrm{cm}}^{-3}$ in helium plasma. The histogram shows 7 bins, each of 2 MeV width.