Quantum electrodynamics of strong fields in heavy ion collision

Quantum electrodynamics of strong external fields is discussed in the context of atomic physics. For sufficiently large electromagnetic coupling constant Zα bound states can approach and even join the antiparticle continuum of the Dirac equation. The resulting possibility of spontaneous positron production and the new concept of a charged electron-positron-vacuum is discussed. The autoionization model and the exact solutions of the single particle Dirac equation are supplemented by a quantum-field-theoretical approach. The influence of vacuum polarization, possible non-linear field effects and the self-screening of extremely strong electrical charges are investigated. (author)