1. Department of Physics, Stanford University, Stanford, California 94305, USA
2. Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, California 94305, USA
3. High Energy Density Science Division, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
4. SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA