Supercomputer simulations have shown scientists a new way to generate controlled beam of gamma rays from lasers. Nearly one million CPU hours on Stampede and Lonestar HPC systems were needed for the particle-in-cell simulation. The Texas Petawatt Laser will use the simulations to guide experimental verification later in 2016. Gamma ray production would make possible basic science research and benefit society through brain imaging, cancer therapy, and anti-terrorist cargo scanning.