ACCUMULATOR    The most important parameter for the accumulator ring is the slippage factor. It is expected to be zero ( isochronous ) so that the proton bunches are frozen longitudinally during accumulation.     As the consequence of selecting the number of bunches as six, the longitudinal space charge during accumulation would not be significant when the bunch is formed with no sharp edge but with a slope where the line density goes to zero in several ns length. This could be realized by adjusting the chopping of the linac micro bunches at low energy.    The rf cavities to compensate for space charge are also out of necessity, and the machine impedance could be fairly low. Given that the accumulation time is only about 400 µs and the accumulated bunches stay in the accumulator only about 60 µs at longest, the instabilities might not be critical issues. However, the longitudinal and transverse microwave instabilities have to be studied and they will set limits to the longitudinal and transverse impedances of the machine.     To know Estimation of the accumulator magnet specifications from the note CERN-AB-2008-060 please here:     - xlsx     - pdf    To know how it looks like in MADX please here :     - ring     - cell     - insert