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.