Nuclear Inst. and Methods in Physics Research, A 895 (2018) 1–9 Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima The design and implementation of a broadband digital low-level RF control system for the cyclotron accelerators at iThemba LABS W.D. Duckitt a, *, J.L. Conradie a , M.J. van Niekerk a , J.K. Abraham a , T.R. Niesler b a iThemba LABS, P.O. Box 722, Somerset West, 7129, South Africa b Stellenbosch University, Stellenbosch, 7600, South Africa ARTICLE INFO Keywords: RF control system Cyclotron FPGA EPICS Digital low-level RF ABSTRACT iThemba LABS has successfully designed a new broadband digital low-level RF control system for cyclotrons, that operates over the wide frequency range of 2–100 MHz and can achieve peak–peak amplitude and phase stabilities of 0.01% and 0.01 ◦ , respectively. The presented system performs direct digital synthesis (DDS) to directly convert the digital RF signals to analog RF and local-oscillator (LO) signals with 16-bit amplitude accuracy, programmable in steps of 1μHz and 0.0001 ◦ . Down-conversion of the RF pick-up signals to an optimal intermediate frequency (IF) of 1 MHz and sampling of the IF channels by 16-bit, single sample-latency 10 MHz ADCs was implemented to allow digital high-speed low-latency in-phase/quadrature (I/Q) demodulation of the IF channels within the FPGA. This in turn allows efficient real-time digital closed-loop control of the amplitude and phase of the RF drive-signal to be achieved. The systems have been successfully integrated at iThemba LABS into the  =8 and  = 10 injector cyclotrons (SPC1, and SPC2), the  = 200 separated sector cyclotron (SSC), the SSC flat-topping system, the pulse-selector system and the , , and -line RF bunchers. The systems have led to a substantial improvement in the beam quality of the SSC at iThemba LABS with a reduction in beam losses by more than 90%. The design, implementation and performance is discussed. 1. Introduction The iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) is a multi-disciplinary accelerator research facility situated near Cape Town, South Africa. At the heart of the facility is the  = 200 separated sector cyclotron (SSC), that delivers particle beams for nuclear physics, nuclear chemistry, neutron therapy, proton therapy, radiobiology and isotope production. Two injector cyclotrons are used as pre-accelerators for the SSC. The first, a  =8 solid pole cyclotron (SPC1) with an internal Penning Ion Gauge (PIG) ion source that produces proton beams with high intensity and the second, a  = 10 solid pole cyclotron (SPC2) that accelerates light and heavy ions from external ion sources. A layout of the facility depicting SPC1, SPC2, the SSC, the SSC flat- topping system, the pulse-selector system and the AX, J, and -line RF bunchers is illustrated in Fig. 1. Fundamental to the operation of the cyclotron systems are the radio frequency (RF) control systems that are responsible for controlling and stabilizing the amplitude and phase of the RF voltages that are used to * Corresponding author. E-mail address: wduckitt@tlabs.ac.za (W.D. Duckitt). accelerate the particles. In total there are 13 RF systems at iThemba LABS that operate at varying frequencies between 2 and 81 MHz and at power levels from 2 W for a buncher system and up to 100 kW for each of the resonators of the SSC. A critical drive has been to replace these 30 year old legacy analog RF control systems with modern technology. To this effect a new broadband digital low-level RF control system has been designed which culminated in the manufacturing of 35 production units. This paper discusses the design, implementation and performance of the new RF control system at iThemba LABS. 2. Design requirements iThemba LABS required the development of new RF amplitude and phase control systems to achieve a greater system stability and reliability for delivering the high intensity beams needed for radioisotope produc- tion as well as beams with improved qualities for nuclear physics and medical radiation. https://doi.org/10.1016/j.nima.2018.03.064 Received 23 November 2017; Received in revised form 19 February 2018; Accepted 22 March 2018 Available online 28 March 2018 0168-9002/© 2018 Elsevier B.V. All rights reserved.