Kutsaev, S.V. Agustsson, R.B. Barcikowski, A. Fischer, R.L. Mustapha, B. Smirnov, A.Yu. Verma, A. JACoW Publishing Geneva, Switzerland 2226-0366 978-3-95450-194-6 10.18429/JACoW-LINAC2018-MOPO077 English 160-162 MOPO077 linac proton coupling operation simulation Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-LINAC2018-MOPO077 http://jacow.org/linac2018/papers/mopo077.pdf A novel concept for an Advanced Compact Carbon Ion Linac (ACCIL) that will deliver up to 1 pnA of carbon ions with variable energy from 45 MeV/u to 450 MeV/u in a 45 m footprint, has been developed by Argonne National Laboratory (ANL) in collaboration with RadiaBeam. The ACCIL will have a 35 MV/m real-estate accelerating gradients that became possible to achieve with the development of novel S-band high-gradient structures, capable of providing 50 MV/m accelerating gradients for particles with β>0.3. In particular, a β=0.3 structure based on the novel approach of operation at the first negative spatial harmonic with the increased distance between the accelerating gaps will be presented. This is the first attempt to reach such high gradients at such small velocities. RadiaBeam and ANL have demonstrated the feasibility of building this structure for accelerating carbon ions by means of advanced computer simulations and are currently working towards the fabrication of this structure for high power tests.