Study of a transversely ellipsoidal bubble and electron trapping of LWFA

Abstract

We present electron trapping in an ellipsoidal bubble in the field of LWFA. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. To explain electron trapping condition, we introduce the relation between the bubble size and the field slope inside and provide an ellipsoidal model of the bubble potential using empirical simulation results. We found that the ellipsoidal potential gives a significantly less restrictive trapping condition than the spherical bubble. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.