Search

The lifetime of the stored beam in storage ring is maintained by a sufficient RF acceleration from a cavity. The longitudinal dynamics of the stored beam is dominated by the RF accelerating voltage of the cavity. There is a discrepancy between the setting RF voltage and the beam dynamics measurement. This affects the beam dynamics studies to maintain a good quality beam to produce a good synchrotron light. The discrepancy should be kept at acceptable value. The activities to clarify this discrepancy such as the cavity voltage measurement with the synchrotron tune, and the calibrating of the RF cavity voltage are performed. Details and results of these activities will be presented.

Femtosecond synchronisation between charged particle beams and external laser systems is a significant challenge for modern particle accelerators. To achieve femtosecond synchronisation of the CLARA electron beam and end user laser systems will require tight synchronisation of several accelerator subsystems. This paper reports on a method to compensate for environmentally driven long-term drift in Laser-RF phase detection systems., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

To increase beam energy in the CLEAR facility at CERN and study the CLIC accelerating structure prototype in operating conditions, the first X-band test facility at CERN was upgraded in 2020. Both, the acquisition and software systems at X-band test stand 1 (Xbox1) were upgraded to exhibit low phase noise which is relevant to klystron based CLIC and to the use of crab cavities in the beam delivery system. The new LLRF uses down-conversion which necessitates a local oscillator which can be produced by two different methods. The first is a PLL, a commonly used technique which has been previously employed at the other X-band facilities at CERN. The second is a novel application of a single sideband up-convertor. The up-convertor system has demonstrated reduced phase noise when compared with the PLL. The commissioning of the new system began in late 2020 with the conditioning of a 50 MW Klystron. Measurements of the quality of the new LLRF will be shown. These will compare the PLL and up-convertor with particular attention on the quality of the phase measurements. Also, a preliminary study of phase shifts in the waveguide network due to temperature changes will be presented., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The Compact Linear Accelerator for Research and Applications (CLARA) facility at STFC Daresbury Laboratory will test underpinning concepts and technology for a next generation X-ray free electron laser (FEL). CLARA will use four S-band normal conducting traveling wave linacs to accelerate electron bunches to a maximum energy of 250 MeV. The amplitude and phase stability of the collected RF systems is critical in enabling CLARA to achieve low (10 fs) shot-to-shot timing jitter of the photon output. Here we present initial measurements and model of the amplitude and phase jitter of the CLARA RF systems, achieved by experimentally correlating the klystron output with controls from modulator, driver, and other environment parameters. The effect of the RF jitter on the CLARA beam momentum is also integrated in the model., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

The High-Luminosity LHC (HL-LHC) crab cavities (CCs) will be installed on both sides of IP1 (ATLAS) and IP5 (CMS) to compensate for the geometric luminosity reduction due to the crossing angle. To cope with the increased beam current (0.55 A DC for LHC, 1.1 A for HL-LHC), the operation of the LLRF system has been changed: rather than fully compensating the transient beam loading, we allow the phase to vary along the turn (100 ps peak-peak with 1.1 A DC). This has been implemented at LHC since July 2017. The CCs have high loaded Q (5e5) and the available RF power is insufficient to follow the bunch phase modulation. The crabbing voltage is not modulated, causing a phase error w.r.t. the individual bunch centroids, leading to transverse kicks of the centroids and an asymmetric crabbing of the bunch cores. We present an analytical model for the resulting luminosity reduction and validate with particle tracking simulations. Due to the symmetry of the bunch filling patterns for the counter-rotating beams, the peak luminosity is reduced by only 2% for nominal HL-LHC parameters at IPs 1 and 5, which is within tolerable limits., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The High Luminosity Upgrade for the LHC (HL-LHC) relies on crab cavities to compensate for the luminosity reduction due to the crossing angle of the colliding bunches at the interaction points. In this paper we present the simulation studies of cavity quenches and the impact on the beam. The cavity voltage and phase during the quench is determined from a simulation in Matlab and used to determine the impact on the beam from tracking simulations in SixTrack. The results of this study are important for determining the required machine protection and interlock systems for HL-LHC., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

CERN’s Compact linear collider (CLIC) will require crab cavities to align the bunches to provide effective head-on collisions. An X-band quasi-TM11 deflecting cavity has been designed and manufactured for testing at CERN’s Xbox-2 high power standalone test stand. The cavity is currently under test and has reached an input power level in excess of 40MW, with a measured breakdown rate of better than 10⁻⁵ breakdowns per pulse. This paper also describes surface field quantities which are important in assessing the expected BDR when designing high gradient structures., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

The use of an injection locked CW magnetron to drive a 2.45 GHz superconducting RF cavity has been successfully demonstrated. With a locking power less than -27 dB with respect to the output and with a phase control system acting on the locking signal, cavity phase was accurately controlled for hours at a time without loss of lock whilst suppressing microphonics. The phase control accuracy achieved was 0.8o r.m.s. The main contributing disturbance limiting ultimate phase control was power supply ripple from the low specification switch mode power supply used for the experiment., Proceedings of the 1st International Particle Accelerator Conference, IPAC2010, Kyoto, Japan

We present the novel beam arrival monitor pickup design currently under construction at Daresbury Laboratory, Warrington, UK. The pickup consists of four flat electrodes in a transverse gap. CST Particle Studio simulations have been undertaken for the new pickup design as well as a pickup design from DESY, which is used as a reference for comparison. Simulation results have highlighted two advantages of the new pickup design over the DESY design; the signal bandwidth is 25 GHz, which is half that of the DESY design and the response slope is a factor of 1.6 greater. We discuss optimisation studies of the design parameters in order to maximise the response slope for bandwidths up to 50 GHz and present the final design of the pickup., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

Six UK institutes are engaged in a collaborative R&D programme with CERN aimed at demonstrating key aspects of technology feasibility for the Compact Linear Collider (CLIC). We give an overview and status of the R&D being done on: 1) Drive-beam components: quadrupole magnets and the beam phase feed-forward prototype. 2) Beam instrumentation: stripline and cavity beam position monitors, an electro-optical longitudinal bunch profile monitor, and laserwire and diffraction and transition radiation monitors for transverse beam-size determination. 3) Beam delivery system and machine-detector interface design, including beam feedback/control systems and crab cavity design and control. 4) RF structure design. In each case, where applicable, we report on the status of prototype systems and performance tests with beam at the CTF3, ATF2 and CesrTA test facilities, including plans for future experiments., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany