115 research outputs found
High CW power, phase and amplitude modulatorrealized with fast ferrite phase-shifters
No full textSuperconducting cavity resonators are suffering from detuning effects caused by high internal electromagnetic fields (Lorentz force detuning). For classical resonators working with continuous wave signals, this detuning is static and compensated by the slow mechanical tuning system. However, pulsing of superconducting cavities, an operational mode only recently considered, results in dynamic detuning effects. New ways to handle this effect have to be found and worked out. A way to supply several superconducting cavities in the particle accelerator by one large transmitter while keeping the possibility of controlling the field in each individual cavity is shown. By introducing a fast phase and amplitude modulator into each cavity feeder line, the individual deviations of each cavity with respect to the average can be compensated in order to equalize their behaviour for the main control loop, which will compensate the global detuning of all cavities. Several types of phase and amplitude modulators suitable for high power RF application, as well as different types of the fast variable phase-shifters for use in the modulator are analysed. The results of the work are foreseen to be applied in the field of particle accelerators but are certainly also interesting for other high power RF domains e.g. tuning devices for industrial microwave heating, plasma applications or nuclear fusion reactors
Digital Measurement System for the HIE-Isolde Superconducting Accelerating Cavities
No full textExtensive R&D efforts are being invested at CERN into the fundamental science of the RF superconductivity, cavity design, niobium sputtering, coating and RF properties of superconducting cavities. Fast and precise characterization and measurements of RF parameters of the newly produced cavities is essential for advances with the cavity production. The currently deployed analogue measurement system based on an analogue phase discriminators and tracking RF generators is not optimal for efficient work at the SM18 superconducting cavity test stand. If exact properties of the cavity under test are not known a traditional feedback loop will not be able to find resonant frequency in a reasonable time or even at all. This is mainly due to a very high Q factor. The resonance peak is very narrow (fraction of a Hz at 100 MHz). If the resonant frequency is off by several bandwidths, small changes of the cavity field during the tuning will not be measureable. Also cavity field will react only very slowly to any change of the drive signal. A new techniques to find and track the cavity resonance faster, as well as to keep the cavity field constant under strong microphonics and helium pressure variations must be found to meet the deadlines for the HIE Isolde machine. Therefore a new fully digital measurement and conditioning system based on the available existing hardware from the LHC and SPS must be designed and built
Transverse feedback: high intensity operation, AGC, IGC, lessons for 2012
No full textThe transverse damper system (ADT) plays an important role in the preservation of the beam transverse emittance and for damping of oscillations driven by the coupled bunch instability. An overview of the ADT system will be presented with an emphasis on the important feedback loop parameters as they change from injection through the ramp into collision. The dedicated setting - up procedure required for the different bunch intensities and bunch spacings will be explained. During the 2011 run the injection and abort gap cleaning became operational at injection energy. Preparations for cleaning at 3.5 TeV as well as batch selective transverse blow - up were completed and preliminarily tested. Plans for 2012 include study and potential improvement of the system impulse response to improve the 'selectivity' of the cleaning and blow - up facility. The ADT also provides bunch - by - bunch observation, which was extensively used during the run and MDs, and will be further upgraded during the next year
ADTOBSBOX to catch instabilities
No full textDuring Long Shutdown 2 (2019–2020) the transverse observation system (ADTObsBox) in the LHC will undergo a substantial upgrade. The purpose of this upgrade is to allow for true low latency, online processing of the 16 data-streams of transverse bunch-by-bunch, turn-by-turn positional data provided by the beam position monitors in transverse feed-back system in the LHC (ADT). This system makes both offline and online analysis of the data possible, where the emphasis will lie on online analysis, something that the older generation was not designed to provide. The new system provides a platform for real-time analysis applications to directly capture the data with minimal latency while also providing a heterogeneous computing platform where the applications can utilize CPUs, GPUs and dedicated FPGAs. The analysis applications include bunch-by-bunch transverse instability analysis which will profit from significant reduction of latency
Operation of the LEP CW Klystrons in Pulsed Mode
No full textFor possible future accelerator projects, as, e. g., the Super-Conducting Proton Linac, SPL, at CERN, it would be desirable to reuse as much of the LEP/RF equipment as possible. In the SPL, as in other proposed proton linacs, pulsed operation is required with RF pulse-lengths varying between 1 and 3 ms and a pulse repetition rate of 50 Hz. The LEP klystrons are equipped with a modulation anode by means of which their beam current and hence the output power can be controlled. In LEP the klystron output power had to be varied very slowly when the energy was ramped. In order to keep a high efficiency also in pulsed mode the rise- and fall-time of the beam pulse in the klystron should be considerably less than 100µs. This goal was achieved by modifying the tetrode modulator, the HV line between modulator and klystron, and the filter network of the HV power supply. SPICE simulations were performed to evaluate the optimum values of capacitors and inductors in the HV filtering network of the LEP 100kV, 40A power converter when a specified DC pulse shape is required and up to eight klystrons are to be powered by one HV supply. These simulations are presented, together with the experimental results obtained on a modified LEP klystron/power converter assembly
Improvement of RF Vector Modulator Performance by Feed-forward Based Calibration
No full textRF Vector Modulator enables independent control of a narrowband RF signal amplitude and phase. Unfortunately practical realization of an analog vector modulator suffers from misbalances and imperfections in the I and Q signal paths. Use of a feed-forward based calibration can compensate for them and significantly improve RF performance and control accuracy of a real vector modulator. Achieved improvements and results on a small series of vector modulator based phase shifters using feed-forward calibration are presented
ADT and RF after LS1
No full textDuring LS1 a number of consolidations and upgrades have been undertaken in the LHC RF, including replacement of a cryomodule (four cavities, beam 2), upgrade of klystron collectors and new solid state crowbar systems. The RF parameters will be outlined in view of the consequences of the increased beam current and energy, and the exotic bunch spacing for the scrubbing beams. The LHC Transverse feedback system (ADT) is also undergoing a major upgrade during LS1, with double the total number of pickups to reduce the noise floor of the system, new beam position electronics and an upgraded digital signal processing system to accommodate all of the extra functionality that had been introduced during LHC Run I, and more sophisticated signal processing algorithms to be deployed for Run II. An external “observation box” to record transverse and longitudinal data from the RF and ADT systems is being implemented
Gain measurements of the LHC transverse feedback system at 3.5 TeV beam energy
No full textThe damping time of the LHC transverse damper has been determined as a function of the electronic gain setting for a non-colliding bunch at 3.5 TeV. The beam was kicked by the Q-kickers and the oscillation of the bunch recorded turn-by-turn using the damper pick-ups. The damping time is calculated from a fit to the measured data. The obtained values serve as a reference to provide a normalization to the programmed gain function as has been implemented in 2011
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