High-energy charged particles are being used to diagnose x-ray-driven implosions in inertial-confinement fusion. Recent measurements with vacuum hohlraums have resulted in quantitative characterization of important aspects of x-ray drive and capsule implosions. Comprehensive data obtained from spectrally resolved, fusion-product self-emission and time-gated proton radiographs with unprecedented clarity reveal new and important phenomena. Several types of spontaneous electric fields differing by two orders of magnitude in strength are observed, the largest being on the order of one-tenth of the Bohr field (, where a0 is the Bohr radius). The hohlraum experiments demonstrate the absence of stochastic filamentary patterns and striations around the imploded capsule, a feature common to direct-drive implosions. The views of spatial structure and temporal evolution of spontaneous electromagnetic fields, plasma flows, implosion symmetry and dynamics provide insight into the physics of x-ray driven implosions. Potential applications for the National Ignition Facility are outlined.