Strong field QED in crystals*

Ultrarelativistic particles in strong crystalline fields of the order 10¹¹ V/cm enable investigations of processes in fields of the order the QED critical field E₀=1.32·10¹⁶ V/cm. Utilizing the relativistic invariance of the parameter χ=γE/E₀, where E is the local electric field, the field may become critical in the rest frame of an electron penetrating a single crystal. In the framework of the CERN NA63 experiment we have obtained experimental results on e.g. quantum synchrotron radiation emission, coherent pairs, radiation reaction and recently trident production in critical fields. Such observations are similar and complementary to what may be obtained from high-power lasers interacting with electrons. An overview of some of the results from the CERN NA63 experiment is presented.