Variable frequency rfq linear accelerator

Abstract

A variable frequency RFQ linear accelerator has a sequence of variable inductance coils connected at intervals along the electrode vanes, such that each coil together with the corresponding section of the vanes forms an LC resonant circuit having a resonant frequency equal to the operating frequency of the accelerator. The variable inductance coils are each comprised of a helical bifilar coil, with each filament of a given coil being connected to one pair of vane electrodes on opposite sides of the beam axis, and a movable shorting bar is provided for each bifilar coil to vary the inductance. The helical bifilar coils in adjacent sections are disposed on opposite sides of the beam axis, the axes of the coils on either side being parallel to the beam axis and mutually coincident. Drive shafts extend along these axes through the wall of the vacuum vessel, with control rods extending radially outward to each of the shorting bars, and a ganging mechanism is provided to control all of the shorting bars so that the LC circuits all maintain the same resonant frequency. The power supply is connected to the vane electrodes through a capacitive impedance. Mode switches are further provided at the ends of the bifilar inductance coils to avoid interfering resonances from the sections of the coils beyond the shorting bars.