Microwave instability criterion for overlapped bunches

Debunching can be a method to measure Z/n of a storage ring by timing the start of microwave instability. However, if this instability begins to show up when two or more bunches overlap each other, the situation becomes more complex, because one is confused of which local current and energy spread should be used. An analysis shows that exactly the same microwave instability criterion should be used as if there is only one bunch.