CUOS Seminar: Magnetics, Underdense Plasma, and Acceleration

Tanner Nutting

Transversely pumped laser driven particle accelerator

We present a new acceleration scheme capable of accelerating electrons and ions in an underdense plasma. Transversely Pumped Acceleration (TPA) uses multiple arrays of counter- propagating laser beamlets that focus onto a central acceleration axis. Tuning the injection timing and the spacing between the adjacent beamlets allows for precise control over the position and velocity of the intersection point of the counter-propagating beam arrays, resulting in an accelerating structure that propagates orthogonal to the direction of laser propagation. We present the theory that sets the injection timing of the incoming pulses to accelerate electrons and ions with a tunable phase velocity plasma wave. Simulation results are presented which demonstrate 1.2 GeV proton beams accelerated in 3.6 mm of plasma and electron acceleration gradients of 2.5 TeV/m in a scheme that circumvents dephasing. This work has potential applications in medical physics, proton radiography, and high energy physics colliders.

Joshua Latham

Cylindrical Magnetic Reconnection Plane in Laser-Plasma Experiment

A self-magnetized annular plasma collided on its interior with a second self-magnetized plasma bubble, demonstrating magnetic reconnection in the radial direction with rotational symmetry. The reconnecting magnetic fields were measured, and significant density jumps were observed at the collision interface. The experiment was conducted at the OMEGA-EP laser facility, where the colliding plasma flows were driven by UV laser beams of 5×10 13 W/cm 2 , and the density and magnetic fields were probed by angular filter refractometry and target-normal-sheet-accelerated-proton radiography, respectively. Results from MHD simulations of the experiment will also be discussed. The results of this experiment given its unique geometry has implications for our understanding of magnetic reconnection in high energy density plasmas.

Veronica Contreras

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.