Prototyping and low-level testing of a 13-MHz digital radio-frequency control system for the PEFP 120-keV heavy ion implanter

The Proton Engineering Frontier Project (PEFP) finished a radio-frequency (RF) implanter. Due to mechanical vibration and temperature slow change in environment, the resonance frequency of the implanter's cavity always drift. For obtaining an optimized beam output performance, a digital frequency control system was designed to regulate the driver frequency for tracking the frequency variation of the cavity. This paper presents the frequency control scheme and digital algorithm implementations. Traditional analog parts, such as phase comparators, analog proportional-integral (PI) controllers, and voltage-controlled oscillator (VCO), in lieu of the above components, a software code was created. The control logic code was written in VHSIC hardware description language (VHDL) language and was implemented on a field programmable gate array (FPGA) board, which was hosted in a versa module europa (VME) mainframe. The main digital control units, including IQ sampling digital phase comparator, digital PI controller, and numerical controlled oscillator (NCO) units were introduced. The algorithm implementation of the control logic, the loop behavior simulation, and the low-level RF experimental test results will be presented.