An SRC includes a stator; a rotator rotatably attached to the stator; and a stack-type cable accommodated in an annular accommodation space defined by the stator and the rotator. The power supply unit includes an analog-to-digital converter. Methods of diagnosing myxomatous valvular disease are also provided. The digital feedback control system also has monitoring inputs and control inputs. As such, during processing, ions are able to penetrate into previously etched features and strike the substrate on the sidewalls of such features.