SIRIUS is a 4th generation synchrotron light source built and operated by the Brazilian Synchrotron Light Laboratory (LNLS). Recently, investigations of noise sources and the storage ring RF plant identification enabled a fine-tuning of the Digital Low-Level Radio Frequency (DLLRF) parameters. This paper presents the main improvements implemented, which include the mitigation of 60Hz noise from the LLRF Front End and the optimization of the control system parameters. Optimizations in the machine were based on an adjusted model of the SIRIUS storage ring RF plant. Tests with the model's parameters showed that the system's stability was strongly dependent on phase shifts introduced by nonlinearities from the high power RF sources. The new parameters significantly improved the control performance, increasing the bandwidth of the system and reducing longitudinal oscillations. BPM (Beam Position Monitor) and BbB (Bunch-by-Bunch) systems were employed to quantify longitudinal beam stability improvements.

Low Level RF (LLRF) control systems of linear accelerators (LINACs) are typically implemented with heterodyne based architectures, which have complex analog RF mixers for up and down conversion. The Gen 3 RF System-on-Chip (RFSoC) device from AMD Xilinx integrates data converters with maximum RF frequency of 6 GHz. That enables direct RF sampling of C-band LLRF signal typically operated at 5.712 GHz without RF mixers, which can significantly simplify the system architecture. The data converters sample RF signals in higher order Nyquist zones and then up or down converted digitally by the integrated data path. The closed-loop feedback control firmware implemented in FPGA integrated in RFSoC can process the baseband signal from the ADC data path and calculate the updated phase and amplitude to be up-mixed by the DAC data path. We have developed an LLRF control RFSoC platform, which targets Cool Copper Collider (C3) and other C or S band LINAC research and development projects. In this paper, the architecture of the platform and the test results for some of the key performance parameters, such as phase and amplitude stability with our custom solid-state amplifier, will be described.

Hefei Infrared Free-Electron Laser device (IR-FEL) is a user experimental device dedicated to energy chemistry research that can generate high brightness mid/far infrared lasers. It is driven by an S-band linear accelerator with a maximum electron energy of 60 MeV. The stability of the final output laser is determined by the energy stability and spread of the electron beam, and the Low-Level RF control system (LLRF) is opitimized to improve the energy stability of the electron beam. There are two klystrons in the linear accelerator of IR-FEL, and the periodic oscillation of out power output of the klytrons is existed (approximately ± 0.2%~2% for amplitude). The oscillation period of two klystrons are exchanged in the case of exchanging the filament power supplies of two klystrons. The pulse-to-pulse feedforward and in-pulse feedback algorithm are developed to compensate the periodic fluctuations of the output power of the klystrons, and the IQ demodulation is changed to the Non-IQ demodulation (13/3) to separate and suppress the odd harmonic. After the optimization, the stability of klystron output signal has been improved from 0.12%/0.07° (rms) to 0.04%/0.09° (rms).

The Hefei Advanced Light Facility (HALF) is a diffraction-limited storage ring-based light source consists of a 180 m linear accelerator and a 480 m storage ring. The RF reference signal included 499.8 MHz and 2856 MHz are generated from two phase-locked master oscillators and transmitted to the RF system, beam position monitor system, timing system and beamline station by the phase stabled coaxial cables which are installed in the ±0.1℃ thermostatic bath. The RF Reference Distribution System (RF-RDS) are developed to realize the phase synchronization and transmission with low phase noise for long distance. The continues wave amplifier is manufactured to generate RF power of 10 W, with the added phase noise being less than 1 fs (10 Hz~10 MHz). The phase noise of each receiving terminal is estimated to be less than 30 fs (10 Hz~10 MHz). The design of RF-RDS and experimental result are discussed in this paper.

SIRIUS is a 4th generation synchrotron light source built and operated by the Brazilian Synchrotron Light Laboratory (LNLS). Recently, investigations of noise sources and the storage ring RF plant identification enabled a fine-tuning of the Digital Low-Level Radio Frequency (DLLRF) parameters. This paper presents the main improvements implemented, which include the mitigation of 60Hz noise from the LLRF Front End and the optimization of the control system parameters. Optimizations in the machine were based on an adjusted model of the SIRIUS storage ring RF plant. Tests with the model's parameters showed that the system's stability was strongly dependent on phase shifts introduced by nonlinearities from the high power RF sources. The new parameters significantly improved the control performance, increasing the bandwidth of the system and reducing longitudinal oscillations. BPM (Beam Position Monitor) and BbB (Bunch-by-Bunch) systems were employed to quantify longitudinal beam stability improvements.

Located in Saskatoon, Saskatchewan, Canada, the Canadian Light Source (CLS) has been operation since 2003. CLS is a 3rd generation Synchrotron Light Source operating at 2.9GeV. The CLS Booster RF system uses a 100 kW, 500 MHz solid-state power amplifier to power two 5-cell “PETRA” cavities. Recently ALBA and CLS collaborated to commission a CLS-constructed version of the ALBA Digital Low-Level RF system in the CLS Booster ring RF system to replace the aging analog low-level RF system. Changes were required to address differing configuration and requirements between the CLS and ALBA RF systems. Challenges and opportunities for system machine safety, reliability, and performance improvements identified during and after commissioning have been addressed. Hardware configuration changes were implemented. Additional hardware devices have been produced and incorporated to streamline interfacing and to mitigate some risks.

In 2023, the KEK-PF 2.5 GeV ring LLRF system was replaced from a conventional analog to an FPGA-based digital system. The hardware and software of our digital LLRF system were developed by customizing the LLRF technologies established at the SPring-8 and J-PARC. In our system, we adopted the non-IQ direct sampling method for RF detection. We set the sampling frequency at 8/13 (307.75 MHz) of the RF frequency, where the denominator (13) is the divisor of the harmonic number (312) of the storage ring. This allows us to detect the transient variation of the cavity voltage that is synchronized with the beam revolution. To compensate this voltage variation, we plan to implement a feedforward technique. These functions will be useful to improve the bunch lengthening performance in a double RF system for KEK future synchrotron light source. The new digital LLRF system has been already installed and used for the user operation. At the nominal beam current of 450 mA, the variation of the cavity voltage amplitude and phase were within ±0.06% and ±0.06°, respectively. In this presentation, we introduce the details of our new system and report on the commissioning results.

One of the crucial control systems of any synchrotron is the Low-Level Radio Frequency (LLRF).  The main purpose of an LLRF is to generate and maintain a stable electric field within the accelerator cavities by controlling its amplitude and phase. SAFRAN Electronic & Defense Spain S.L.U. is currently developing the new digital LLRF to update the system in the ALBA Synchrotron Light facility located in Barcelona. The design, implementation and tests are based on ALBA technical specifications. It is expected that the system will be tested on site, in its 500 MHz version, by summer 2024 while the 1.5 GHz (third harmonic version) will be tested on site by the first quarter of 2025. The architecture, design, and development as well as the performance of the LLRF system will be presented in this work.

Identifying the source of beam loss events in the CEBAF accelerator can be a challenging task. Determining whether an RF cavity with an unannounced gradient or phase transient is the culprit would be a valuable tool for operations staff in addressing recurring beam loss incidents. A prototype offline system was developed in the fall of 2022, utilizing a dispersive beam position monitor (BPM) and the existing switched electrode electronics BPM hardware. A commercial off-the-shelf data acquisition (DAQ) system was employed to capture BPM wire signals at a sample rate of 20 kS/s. The system was triggered by the fast shutdown signal, which disables the beam at the injector. Analysis of beam position and energy variation before a beam loss event was used to determine if the beam loss event was associated with an energy transient. The prototype system, implemented using National Instruments hardware and LabVIEW software, relied on a software trigger. Manual post-processing was required to ascertain whether the fault was due to an un-tripped cavity with a gradient or phase transient. This work presents a production-quality system that utilizes the same data acquisition hardware developed and installed in CEBAF to monitor the time domain RF control signals in the legacy analog RF systems. As the new system employs a hardware trigger, developing tools to automatically identify faults linked to energy transients unrelated to cavity faults will be straightforward.

SPARC_LAB facility was born in 2004 as an R&D activity to develop a high brightness electron photo-injector dedicated to FEL experiments and exploration of advanced acceleration techniques. The electron source consists in a brazefree 1.6-cell S-band RF gun with a peak electric field of 120 MV/m and a metallic copper photocathode. The gun injects particles into two S-band sections, the initial section acting as an RF compressor using the velocity bunching technique, with built-in solenoid coils that enhance magnetic focusing and control emittance. A subsequent C-band acceleration section acts as a booster to achieve the desired kinetic energy. The Lazio Regional government recently funded the SABINA project for the consolidation of SPARC_LAB facility. The reference and the distribution systems and the Low Level radiofrequency (LLRF) system will also undergo a significant upgrade, involving the replacement of the original analogue S-band and digital C-band radiofrequency systems with commercial, temperature-stabilized, FPGA-controlled LLRF digital systems provided by Instrumentation Technologies in order to improve performance in terms of amplitude, phase resolution, and stability.