Beamlet is a single beamline, nearly full scale physics prototype of the 192 beam Nd:Glass laser driver of the National Ignition Facility. It is used to demonstrate laser performance of the NIF multipass amplifier architecture. Initial system characterization tests have all been performed at pulse durations less than 10 ns. Pinhole closure and modulation at the end of long pulses are a significant concern for the operation of NIF. We recently demonstrated the generation, amplification and propagation of high energy pulses temporally shaped to mimic 20 ns long ignition pulse shapes at fluence levels exceeding the nominal NIF design requirements for Inertial Confinement Fusion by Indirect Drive. We also demonstrated the effectiveness of a new conical pinhole design used in the transport spatial filter to mitigate plasma closure effects and increase closure time to exceed the duration of the 20 ns long pulse
