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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

CERN’s Antiproton Decelerator (AD) started operating for physics in July 2000 and has been successfully providing experiments with antiprotons since then. Stacking antiprotons at injection energy was foreseen as a special operational mode to be used if high intensity per pulse was required for special physics needs. The implementation of antiprotons stacking at injection was commissioned in 2000 through a series of machine development sessions. Although some operation for AD users was done in this mode, the increase in intensity per cycle was offset by a longer cycle required, hence little increase in antiproton flux was obtained. This operational mode was neither been requested nor used since then. AD is being consolidated during Long Shutdown 2 (LS2). Stacking operation is not planned as baseline operation for the AD but might be required later on. This note summarises the AD side of the procedures carried out to perform stacking at injection energy during fall 2000. Its aim is to document, for future reference, methods used, problems encountered and solutions found. Some unpublished beam results are also given.

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

At the CERN Proton Synchrotron Booster, PSB, an analog transverse damper system has been in operation since 1999, providing satisfactory operational results with the proton beam supplied by Linac2. As a consequence of the LHC Injectors Upgrade, the PSB will face new challenges imposed by higher intensity, injection and extraction energy. In this framework, the transverse feedback system is subject to an upgrade to adapt to the expected Linac4 beam and to the demands for new features including transverse blow-up, beam excitation for optics measurements and new remote control and monitoring capabilities. The replacement of the aging electronic hardware is also recommended to improve the system maintainability for future years. During 2018 a new digital transverse feedback electronics was installed in the PSB, in parallel with the current operational one, offering for the first time the occasion to demonstrate its performance with beam. Encouraging results were obtained such as the suppression of beam instabilities at all PSB energies and intensities. In this paper we describe the steps undertaken in 2018 in order to commission the system with the main goal to accelerate and extract the highest intensity beams produced at the PSB., 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

In 2017 the CERN Low Energy Ion Ring demonstrated once more the feasibility of injecting, accumulating, cooling and accelerating a new nuclei, 129Xe39 . The operation of this new ion species started at the beginning of March with the start up of the xenon ion source and the Linac3. Ten weeks later the beam arrived to the Low Energy Ion Ring (LEIR) triggering the start of several weeks of beam commissioning in view of providing the injector complex with Xenon beams for different experiments and a series of machine development experiments in LEIR. Two types of beams were setup, the so called EARLY beam, with a single injection into LEIR from Linac3, and the NOMINAL beam with up to seven injections. 2017 was as well an interesting year for LEIR because several improvements in the control system of the accelerator and in the beam instrumentation were done in view of increasing the machine reliability. This paper summarises the beam commissioning phase and all the improvements carried out during 2017., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

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

Longitudinal painting has been presented as an elegant technique to fill the longitudinal phase space at injection to the CERN PSB once it is connected with the new Linac4. Painting brings several advantages related to a more controlled longitudinal filamentation, lower peak line density and beating reduction, resulting in a smaller space-charge tune spread. This could be an advantage especially for high intensity beams (> 6·10¹² protons per bunch) to limit losses on the transverse acceptance of the machine. This paper presents an overview on the possible advantages of the technique for operational and test beams, taking care of the hardware limitations and possible failure scenarios., 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

The LHC performance during the proton-lead run in 2016 fully relied on a permanent monitoring and systematic improvement of the beam quality in all the injectors. The beam production and characteristics are explained in this paper, together with the improvements realized during the run from the source up to the flat top of the LHC. Transmission studies from one accelerator to the next as well as beam quality evolution studies during the cycle at each accelerator, have been carried out and are summarized in this paper. In 2016, the LHC had to deliver the beams to the experiments at two different energies, 4 Z TeV and 6.5 Z TeV. The properties of the beams at these two energies are also presented, Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

MD210 aims for the creation of longitudinally hollow bunches in the CERN PS Booster. The first three sessions have been carried out using the radial loop feedback system in order to drive the beam on a dipolar parametric resonance (instead of the phase loop). It has been found that the damping by the phase loop inhibits the excitation of the resonance to a major extent. The hollow distributions generated under these circumstances fail to reach a satisfying bunching factor. Nonetheless, proving the principally successful application of this technique to the PS Booster promises good results once the phase loop system supports trim functions. The approach, actions and detailed results of the first three MD sessions are presented in this paper.

The renewed availability of heavy ions at CERN for the needs of the LHC programme has triggered the interest of the fixed-target community. The project, which involves sending several species of primary ions at various energies to the North Area of the Super Proton Synchrotron, has now entered its operational phase. The first argon run, with momenta ranging from 13 AGeV/c to 150 AGeV/c, took place from February 2015 to April 2015. This paper presents the status of the project, the performance achieved thus far and an outlook on future plans., 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

CERN’s Proton Synchrotron Booster (PSB) is undergoing a major upgrade program in the frame of the LHC Injectors Upgrade (LIU) project. During the first long LHC shutdown (LS1) some parts of the upgrade have already been implemented, and the machine has been successfully re-commissioned. More work is planned for the upcoming end-of-year technical stops, notably in 2016/17, while most of the upgrade is planned to take place during the second long LHC shutdown (LS2). We report on the upgrade items already completed and commissioned, the first Run 2 beam performance and give a status of the ongoing design and integration work., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

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

The first LHC proton-ion run took place in January-February 2013; it was the first extension to the collider programme, as this mode was not included in the design report. This paper presents the performance of the heavy ion and proton production complex, and details the issues encountered, in particular the creation of the same bunch pattern in both beams.

To reach a luminosity higher than 6×1027 Hz/cm2 for Pb-Pb collisions, as expected by the ALICE experiment after its upgrade during the 2nd Long LHC Shutdown (LS2), several upgrades will have to be performed in the CERN accelerator complex, from the source to the LHC itself. This paper first details the present limitations and then describes the strategy for the different machines in the ion injector chain. Both filling schemes and possible hardware upgrades are discussed.

Since the CERN PS Booster cannot simultaneously provide the beam brightness and intensity required, the nominal (25ns bunch spacing) proton beam for the LHC involves double-batch filling of the PS machine. Linac 4, which is under construction, will eventually remove this restriction. In the meantime, the request for 50 and 75ns bunch spacings to mitigate electron cloud effects has lowered the intensity demand such that the Booster can meet this in a single batch without compromising beam brightness. Single-batch transfer means providing two bunches from each of three Booster rings and, in turn, that the bunch spacing is modified by the addition of an h=1 rf component to the h=2 in the Booster in order to fit the h=7 rf buckets waiting in the PS (whilst leaving one bucket empty for kicker purposes). Following the first experiments performed in 2008, the rf manipulations in the Booster have been refined and those in the PS have been modified to cope with single-batch beams. This latest work is presented for both the 50 and 75ns variants., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

The Low Energy Ion Ring (LEIR) is an accumulation ring in the Large Hadron Collider ion injector chain. After its successful start in 2005, it has been running in three operational campaigns. The LEIR LLRF system is the first all-digital low-level RF (LLRF) system to be made operational in a CERN circular machine. Composed of modular VME 64X hardware, it carries out extensive digital signal processing via Field Programmable Gate Arrays and Digital Signal Processors. System capabilities include beam control tasks, such as frequency program, beam phase, radial and synchronization loops, as well as cavity voltage/phase loops. All the system¿s control parameters are fully configurable, remotely and in-between cycles; extensive built-in diagnostics and signal observation features are available. The system has proven to be not only flexible and powerful but also extremely reliable. This is very important as the LEIR LLRF system is the pilot project for the LLRF renovation of other CERN¿s machines. This paper gives an overview of the main system building blocks and outlines their capabilities and operational features, along with results obtained during the first years of beam operation., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In 2008 a project was started to renovate the CERN’s PS Booster (PSB) low-level RF (LLRF). Its aim is to equip all four PSB rings with modern LLRF systems by 2013 at the latest. Required capabilities for the new LLRF include frequency program, beam phase, radial and synchronization loops. The new LLRF will control the signals feeding the three RF cavities present in each ring; it will also shape the beam in a dual harmonic mode, operate a bunch splitting and create a longitudinal blow-up. The main benefits of this new LLRF are its full remote and cycle-to-cycle controllability, built-in observation capability and flexibility. The overall aim is to improve the robustness, maintainability and reliability of the PSB operation and to make it compatible with the injection from the future LINAC4. The chosen technology is an evolution of that successfully deployed in CERN’s ion accumulator ring LEIR and it is based upon modular VME 64X hardware and extensive digital signal processing. This paper outlines the main characteristics of the software and hardware building blocks. Promising initial beam tests are shown and hints are included on the main milestones and future work., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

In the framework of the LHC Injector Upgrade (LIU) project the radio-frequency (RF) systems of the synchrotrons in the LHC injector chain will undergo significant improvements to reach the high beam intensity and quality required by the High-Luminosity (HL) LHC. Following the recent upgrade of the longitudinal beam control system in the PS Booster (PSB), tests with Finemet cavities are being performed in view of a complete replacement of the existing RF systems in the PSB by ones based on this technology. In the PS a similar wide-band Finemet cavity has been installed as a longitudinal damper. New 1-turn delay feedbacks on the main accelerating cavities to reduce their impedance have also been commissioned. Additional feedback and beam control improvements are foreseen. A major upgrade of the main RF system in the SPS by regrouping sections of its travelling wave cavities, increasing the number of cavities from four to six, will reduce beam-loading and allow higher intensities to be accelerated. The upgrade includes the installation of two new RF power plants and new feedback systems. All upgrades will be evaluated with respect to their expected benefits for the beams to the LHC.

In order to increase the transverse brightness of beams for the LHC, ever more complicated RF manipulations have been proposed in the PS machine to reduce the intensity demands per PS batch on the upstream PS Booster. Several schemes based on cascades of batch compression, bunch merging, as well as the more routine bunch splitting have been successfully commissioned and higher brightness beams have been delivered to the downstream accelerators for measurement. Despite all this complexity, longitudinal and transverse beam quality are well preserved. In addition, to profit fully from the brightness of all four PS Booster rings, the injection of twice 4 bunches into harmonic 9 buckets in the PS has been made operational as an alternative to the usual double-batch transfer of 4 + 2 bunches into harmonic 7. This paper summarizes the new beam production schemes, their implementation in the PS low-level RF system and the experimental results..