Zimmermann, F. JACoW Geneva, Switzerland 978-3-95450-187-8 10.18429/JACoW-eeFACT2016-MOT3AH2 English 25-31 MOT3AH2 ion collider luminosity emittance operation Contribution to a conference proceedings 2017 2017-07 https://doi.org/10.18429/JACoW-eeFACT2016-MOT3AH2 http://jacow.org/eefact2016/papers/mot3ah2.pdf Designs for future high-energy circular electron-positron colliders are based on both established and novel concepts. An appropriate design will allow these facilities to serve not only as ‘‘Higgs factories'', but also as Z, W and top factories, and, in addition, to become a possible first step to a higher-energy hadron collider.