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CERN’s Antiproton Decelerator (AD) has been re-furbished to provide reliable operation for the Extra Low ENergy Antiproton ring (ELENA). In particular, AD was equipped with a new digital Low-Level RF (LLRF) system that was successfully commissioned during the summer 2021. The new AD LLRF system has routinely captured and decelerated more than 3·10⁷ antiprotons from 3.5 GeV/c to 100 MeV/c in successive steps, referred to as RF segments, interleaved by cooling periods. The LLRF system implements the frequency program from Btrain data received over optical fiber. Beam phase/radial and cavity amplitude/phase feedback loops are operated during each RF segment. An extraction synchronization loop is triggered on the extraction RF segment to transfer a single bunch of antiprotons to ELENA. Extensive diagnostics features are available and operational modes such as bunched beam cooling and bunch rotation have been successfully deployed. The LLRF parameters can be different for each RF segment and are controlled by a dedicated application. This paper gives an overview of the AD LLRF beam commissioning results obtained and challenges overcome. Hints on future steps are also provided., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

As part of the LHC Injectors Upgrade, the CERN Proton Synchrotron Booster (PSB) has been upgraded with new wide-band Finemet cavities and a renovated Low-Level Radio Frequency system with digital cavity controllers implemented in FPGAs. Each controller synchronously receives the computed revolution frequency, used to generate 16 harmonic references. These are then used to IQ demodulate the voltage gap and modulate the 16 RF drive signals each controlled through a Cartesian feedback loop (with individual voltage and phase control). The sum of these digital drive signals is then sent to the cavities. In addition, a configurable blow-up system providing a sinusoidal or custom noise pattern can be used to excite the beam. An embedded network analyzer allows studying the stability of the feedback loops of the individual harmonics. The 16 harmonic feedback loops have been successfully operated during 2021, allowing to reduce the beam induced voltage and control the longitudinal emittance of the beam. In this paper we present the system architecture as well as the performance of the complete cavity controller during operation in the PSB., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

To provide HL-LHC performance, the CERN LHC injector chain underwent a major upgrade during an almost 2-year-long shutdown. In the first half of 2021 the injectors were gradually re-started with the aim to reach at least pre-shutdown parameters for LHC as well as for fixed target beams. The strategy of the commissioning across the complex, a summary of the many challenges and finally the achievements will be presented. Several lessons were learned and have been integrated to define the strategy for the performance ramp-up over the coming years. Remaining limitations and prospects for LHC beam parameters at the exit of the LHC injector chain in the years to come will be discussed. Finally, the emerging need for improved operability of the CERN complex will be addressed, with a description of the first efforts to meet the availability and flexibility requirements of the HL-LHC era while at the same time maximizing fixed target physics output., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The PS Booster (PSB) is the first synchrotron in the injection chain for protons. The beams produced for the LHC and various fixed target experiments cover a very large parameter space. Over the Long Shutdown 2 (LS2), the PSB was heavily upgraded as part of the LHC Injectors Upgrade (LIU) project. The low-level RF systems now drive the new Finemet-loaded cavities, control RF synchronisation for the new injection mechanism, and cope with the increased injection and extraction energies. The Finemet cavities provide exceptional flexibility, allowing an arbitrary distribution of voltage at different revolution frequency harmonics, but at the cost of significant broadband impedance. The new injection mechanism allows bunch-to-bucket multi-turn injection, which significantly reduces the amount of beam loss at the start of the cycle. The longitudinal beam production schema for each beam-type was developed based on simulations during LS2, and then adapted during the setting-up phase to suit the final operational configuration. This paper discusses the commissioning of the new LLRF, and the consequences of the LIU upgrades on the production of various beams., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Over CERN’s Long Shutdown 2, the conventional ferrite-loaded cavities of the PS Booster were replaced with wide-band Finemet-loaded cavities. The Finemet cavities bring many operational advantages, but also represent a significant broadband impedance source. The impedance is mitigated by servo loops, which suppress the induced voltage, reducing the impedance as seen by the beam. Accurately including the impedance of the cavity and the effect of the servoloops in longitudinal tracking simulations is essential to predict the performance with beam. This paper discusses the results of a measurement campaign, which is intended to give a direct measurement of the cavity impedance. Using the detected voltage and the measured beam profile, the cavity impedance can be inferred and used to improve beam dynamics modelling., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Extra Low ENergy Antiproton storage ring (ELENA) is an upgrade project at the CERN AD (Antiproton Decelerator). ELENA will further decelerate the 5.3 MeV antiprotons coming from the AD down to 100 keV. ELENA features electron cooling for emittance control during deceleration thus preserving the beam intensity and allowing to extract bright bunches towards the experiments. The lower energy will allow for increasing the antiproton trapping efficiency up to two orders of magnitude, which is typically less than 1% with the present beam from AD. The ring was completed with the installation of the electron cooler at the beginning of 2018. Decelerated beams with characteristics close to the design values were obtained before the start of CERN Long Shutdown 2 (LS2). During LS2 electrostatic transfer lines from the ELENA ring to the experimental zones will be installed, replacing the magnetic transfer lines from the AD ring. The latest results of commissioning with H⁻ and antiprotons and the first observation of electron cooling in ELENA will be presented, together with an overview of the project and status and plans for LS2 and beyond., Proceedings of the North American Particle Accelerator Conference, NAPAC2019, Lansing, MI, USA

Electron cloud (e-cloud) effects are among the main performance limitations for the operation of the Large Hadron Collider (LHC) with 25 ns bunch spacing. A large number of electrons impacting on the beam-screens of the superconducting magnets induces significant heat load, reaching values close to the full cooling capacity available from the cryogenic system. A number of Machine Development (MD) sessions in 2018 was dedicated to characterizing the heat load as a function of beam and machine parameters, investigating in particular its distribution along the ring and its dependence on the filling pattern, bunch population and bunch length. The main results of these measurements have been compared against simulations performed with the PyECLOUD code in order to validate the underlying model.

CERN’s Extra Low ENergy Antiproton (ELENA) ring underwent its second full year of beam commissioning in 2018. The commissioning was very successful, although delayed by recurrent lack of beam availability from the H- source as well as from the Antiproton Decelerator (AD) ring. Major achievements of the ELENA commissioning in 2018 included the deployment of all required features in its Low-Level RF (LLRF) system, the commissioning of the electron cooler and the delivery of extracted beam to the Gravitational Behaviour of Antihydrogen at Rest (GBAR) experiment. This note describes the LLRF functionalities deployed during the 2018 ELENA run together with the main beam results obtained and some problems encountered. Remaining tasks to be integrated and validated are also summarised. This note is not only a general documentation of what has been achieved. First and foremost this note is intended to contribute in the training of LLRF experts and OP / ABP colleagues, in view of the future ELENA LLRF operation. Owing to the similarities between ELENA and the AD machine, this note will also be useful for the development and commissioning of the post-Long Shutdown 2 (LS2) AD LLRF, based upon the same system.

CERN’s new Extra Low ENergy Antiproton accelerator/decelerator (ELENA) completed its initial commissioning in 2018. This machine is equipped with a new digital Low-Level RF (LLRF) system that implements beam and cavity loops as well as longitudinal diagnostics. ELENA’s LLRF was instrumental for machine commissioning by decelerating some 1 E7 antiprotons from 5.3 MeV to 100 keV. Commissioning with H⁻ ions took also place. Challenges faced included coping with low beam intensity and the wide frequency swing. This paper gives an overview of the LLRF system capabilities and operation. Beam results achieved with both H⁻ ions and antiprotons are also shown., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The Antiproton Decelerator (AD) has been routinely providing 3 E7 antiprotons since July 2000 at 100 MeV/c from 3.5 GeV/c. It will be refurbished during the Long Shutdown 2 (LS2) to provide reliable operation for the new Extra Low ENergy Antiproton (ELENA) ring. AD will be equipped with a new digital Low-Level RF (LLRF) system before its restart in 2021. Diagnostics to measure beam intensity, Δp/p and Schottky spectra will also be developed. This paper is an overview of the planned capabilities and implementations, as well as of the challenges to overcome., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The CERN PS Booster (PSB) is the first circular accelerator in the LHC proton injector chain. The upgrade of this four-ring machine is underway within the framework of the LHC Injectors Upgrade project. The existing digital Low-Level RF (LLRF) system will also be upgraded. This paper outlines the LLRF capabilities required, their implementation and the challenges involved. Results of tests carried out to prepare for the LLRF upgrade are given., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

CERN’s Extra Low ENergy Antiproton (ELENA) ring’s commissioning with beam started in earnest in March 2017. Ions from an H- source were injected in ELENA at low energy, although in a degraded way (lower voltage and intensity than planned) and with not constant reproducibility of the injection. From August 2017 onwards antiprotons from the AD were also injected in ELENA at high energy for up to three, weekly MD session. The 2017 ELENA commissioning run stopped on December 1st to allow the installation of the electron cooler. This note gives an overview of the successful operation carried out by the ELENA Low-Level RF (LLRF) during the first year of ELENA commissioning and of the main beam results obtained. Operation with H- ions and with antiprotons are considered, together with different operational settings and problems encountered. Hints on future deployment and commissioning steps are also provided.

The CERN Extra Low ENergy Antiproton ring (ELENA) intended to decelerate anti-protons from the CERN Antiproton Decelerator from 100Mev/c to 13.7MeV/c, has been equipped with an orbit measurement system consisting of 10 horizontal and 10 vertical electrostatic pick-ups. Using charge amplifiers the signals are converted into sum and difference signals that, once digitalized, are down converted to baseband and used to calculate intensity independent beam positions. The system is implemented on seven VME switched serial based FPGA / DSP boards carrying direct digital synthesisers and analogue to digital converters on standard FPGA mezzanine cards. The switched serial high-speed bus allows intercommunication between DSPs and thus averaging of the signals from all pick-ups in real-time to be used either in the RF radial feedback system or for longitudinal Schottky diagnostics. The system implementation and initial orbit measurements with the H⁻ beam used for ELENA commissioning will be presented, as well as future upgrades for trajectory and longitudinal Schottky measurements., Proceedings of the 6th Int. Beam Instrumentation Conf., IBIC2017, Grand Rapids, MI, USA

The Extra Low ENergy Antiproton (ELENA) decelerator is under commissioning at CERN. This decelerator is equipped with a new digital low-level RF (LLRF) system, in-house developed and belonging to the LLRF family already deployed in CERN's PS Booster and Low Energy Ion Ring (LEIR) synchrotrons. New features to adapt it to the demanding requirements of ELENA's operation include new, low noise ADC daughtercards and a fixed-frequency clocking scheme. This paper gives an overview of the LLRF system; initial beam results are also shown together with hints on the future system upgrade., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A prototype wideband High-Level RF (HLRF) sys-tem based on Finemet metal alloy has been installed in CERN's PS Booster (PSB) Ring 4 in 2012, within the frame of the LHC Injectors Upgrade (LIU) project. A digital Low-Level RF (LLRF) system was used to control the HLRF system to ascertain the capabilities of the combined system, especially under heavy beam loading. The testing campaign was satisfactory and in 2015 the CERN management decided to replace all ferrite-based systems with Finemet ones for the PS Booster restart in 2020. This paper describes the LLRF features implemented for operating the wideband HLRF system and the main beam results obtained. Hints on the LLRF evolution in view of the PSB HLRF renovation are also given., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

CERN's Low Energy Ion Ring (LEIR) low-level RF (LLRF) system has been successfully upgraded in 2016 to the new digital, LLRF family for frequency-sweeping synchrotrons developed at CERN. For LEIR it implements not only beam loops but also the voltage and phase loops required for the control of two Finemet-based High-Level RF (HLRF) systems. This paper gives an overview of the system and of new requirements implemented, such as the parallel operation of two HLRF systems. Beam results for the 2016 lead ions run are also shown., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The four rings of CERN's PS Booster have been equipped in 2014 with a new digital low-level RF (LLRF) system based upon a new, in-house developed LLRF family. This is a second-generation LLRF family that has been since then deployed on other synchrotrons. The paper provides an overview of the system's commissioning and first years of operation. In particular, an overview is given of the main system features and capabilities, such as beam loops and longitudinal beam blowup implementation. Operational improvements with respect to the previous, analogue digital LLRF are also mentioned, together with the planned system evolution to satisfy new requirements., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

For the High Luminosity upgrade the β* in IR1 and IR5 will be further reduced compared to the current LHC. As the β* decreases the β-functions in the inner triplet (IT) increase resulting in a higher sensitivity of the HL-LHC to ground motion in the IT region or to increases of the low frequency noise. Noise can in general lead to emittance growth and higher halo population and diffusion rate. However, it is usually assumed in the literature that only frequencies close to the betatron frequencies and sidebands have an effect on the emittance and tail population. To test this theory, an MD was carried out to observe if also low frequency noise can lead to emittance growth and stronger halo population and diffusion.

The LHC collimation system is designed to provide effective cleaning against losses coming from off-momentum particles, either due to un-captured beam or to an unexpected RF frequency change. For this reason the LHC is equipped with a hierarchy of collimators in IR3: primary, secondary and absorber collimators. After every collimator alignment or change of machine configuration the off-momentum cleaning efficiency is validated with loss maps at low intensity. We describe here the improved technique used in 2015 to generate such loss maps without completely dumping the beam into the collimators. The achieved performance of the collimation system for momentum cleaning is reviewed., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

For the renovation and upgrade of the CERN PS Booster (PSB) RF systems a development project was launched in 2012. The design, based on a new approach, aimed at replacing the existing tuned, narrowband RF systems with wideband, modular, solid-state driven units. A wide range of issues had to be addressed spanning from RF power production, radiation hardness of solid-state devices, active cancellation of beam-induced voltages, dedicated low-level electronics allowing multi-harmonic operation and beam stability. Following a three-year prototyping and testing campaign and two international reviews, the project endorsement came at the end of year 2015. It foresees the complete removal of present h1, h2 and h10 systems and the deployment of a new one covering all the frequency ranges from 1 MHz to 18 MHz. The four PSB rings will be equipped with 144 identical acceleration cells providing 24 kV total RF voltage per ring. This paper describes the design concepts, the retained solutions, the expected performances and includes the procurement and implementation strategies. This activity is part of the LHC Injectors Upgrade project (LIU)., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

In the framework of the LHC Injectors Upgrade project (LIU) and in view of a complete replacement of the existing CERN PS Booster (PSB) RF systems, a small scale, wide band prototype cavity was installed in 2012 in the machine. Following the encouraging tests done using this limited set up, an almost full scale, RF system prototype has been built and installed in the PSB during the Long Shutdown 1 (LS1). This modular, Finemet® loaded system covers the band 0.5 / 4 MHz corresponding to the h=1 and h=2 frequency ranges. It uses solid-state power stages and includes fast RF feedback for beam loading compensation. New dedicated digital low level electronics have been implemented for all loops required for beam acceleration and interfaces with the general PSB control system. It allows using the new equipment at the fundamental and/or second harmonic of the beam revolution frequency as well as operating it in parallel with the existing RF systems. This paper describes the low level and power sections of the project and reports about the achieved results and experience built up so far., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Unbunched beam is a potentially serious issue in the LHC as it may quench the superconducting magnets during a beam abort. Unbunched particles, either not captured by the RF system at injection or leaking out of the RF bucket, will be removed by using the existing damper kickers to excite resonantly the particles in the abort gap. Following beam simulations, a strategy for cleaning the abort gap at different energies was proposed. The plans for the commissioning of the beam abort gap cleaning are described, and the first results from the beam commissioning are presented., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan