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E-beam systems of voltages greater than one million volts (1MV) are integral in design. This means the power supply and accelerator share the same pressure vessel. The majority of the systems that have voltages less than or equal to one million volts (1MV) are cable-connected. The Cable-Bushing Assembly is required to conduct the voltage from the power supply to the accelerator. A simple wire will not suffice because of the extremely high voltage.
This assembly can be divided into five parts: the cable, two terminations and two bushings. The high voltage cable is made up of oil-impregnated paper, wound on a hollow core of copper conductors. Two copper foil shields surround the paper, and an outer jacket of polyethylene encloses the cable. The transition from the gas insulation in the power supply and accelerator to the oil-impregnated paper insulation of the cable is achieved by the bushings. The bushing is a casting of epoxy. Within the casting is a metal shield used to organize the electrostatic field lines. A termination is attached to each end of the cable. The termination works with the bushing’s metal shield to insure the proper voltage gradient. The termination is a coil of extra paper called a paper stress cone, which builds up the thickness of the cable’s insulation. The shield of the cable is extended over half of this cone, and is connected to the metal shield within the bushing. Without the bushing and termination, the voltage would spark across the end of the cable.
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