Channel Formation and Transverse Ion Acceleration from High-Intensity Laser Interactions with Underdense Plasma on OMEGA EP

Experiments were performed at the OMEGA EP laser facility to study the direct laser acceleration (DLA) of electrons in an underdense plasma created from a helium gas target. In these experiments, the ponderomotive force expels electrons from the regions of highest laser intensity to form a channel. The charge separation creates a strong transverse electric field that accelerates ions radially through a Coulomb explosion; it is the same radial channel field, along with the electron beam-generated azimuthal magnetic field, that facilitates DLA. Since the channel formation is key to understanding electron acceleration, the transversely accelerated helium ions, measured with a Thomson Parabola Ion Energy (TPIE) spectrometer, provide an interesting complementary measurement for understanding the electric field strengths inside the channel. Furthermore, from data collected with a proton probe we aim to understand the properties of the channel fields, the same fields from which the ions have been accelerated.