Summary of Working Group 4: Application of compact and high-gradient accelerators

We present here an overview of the topics presented and discussed during the Working Group 4 sessions of the European Advanced Accelerator Concepts workshop 2019 (EAAC19). The remit of Working Group 4 (WG4) is to address topics relating to all potential application areas of compact and high-gradient accelerators. This includes recent experimental results and planned demonstration experiments with relevance to radiation generation, medical, industrial, and cultural heritage sector applications, and development of advanced photon sources such as free electron lasers (FEL). Within scope of Working Group 4 is also discussions on planned facilities implementing advanced accelerator concepts that have a focus on applications, as well as beam shaping and tailoring to deliver adequate beams for applications. The topics discussed in the EAAC19 programme for Working Group 4 all fit within the following application theme areas: 1) new facilities exploiting advanced and novel accelerator concepts, 2) development of next generation photon sources, 2) imaging and spectroscopy with laser-plasma accelerator particle and photon beams, and 3) radiobiology with laser-plasma accelerator particle beams.