Effect of halo on the stability of electron bunches in laser wakefield acceleration

The stability of short electron bunches formed and accelerated by laser wakefield in gas jets strongly depends on parameters of pre-plasma due to poor pulse focus-ability. Instabilities provoked by light energy remained out of focus spots (halo), usually 30–50%, are shown to result in broad and spotted transverse distributions of electrons in uniform gas jets radiated by high-contrast laser pulses. Shaped pre-plasma may drastically improve pulse focus-ability with stable, well-pointed, and well-collimated electron bunches.