289 research outputs found

    Simulation of LHC Bunches under Influence of 50-Hz-multiple Lines on the Cavity Field

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    The effect of coherent lines at multiple of 50 Hz, with amplitudes as measured in the test stand, on the longitudinal emittance of LHC proton bunches was studied by simulation. In the absence of other effects it was found that the measured noise gives a negligible effect

    Voronoi Particle Merging Algorithm for PIC Codes

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    We present a new particle-merging algorithm for the particle-in-cell method. Based on the concept of the Voronoi diagram, the algorithm partitions the phase space into smaller subsets, which consist of only particles that are in close proximity in the phase space to each other. We show the performance of our algorithm in the case of the two-stream instability and the magnetic shower.Comment: 11 figure

    Realistic RF system and Beam Simulation in Real Time for a Synchrotron

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    Due to heavy beam loading with gaps in the LHC beams, RF and beam are intimately linked to a complex system with fast transients where the RF loops and their limitations play a decisive role. Such a system is difficult to assess with analytical methods. To learn about overall system stability and for the definition of RF components to be built it is essential to understand the complete system long before the machine really exists. Therefore the author has written a general purpose real time simulation program and applied it to model the LHC machine with its beam pattern and complete double RF system. The latter is equipped with fast RF vector feedback loops having loop delay, transmitter power limitation and limited amplifier bandwidth as well as including one-turn-delay feedback and longitudinal batch injection damping. The development of all RF and beam quantities can be displayed graphically turn by turn. These frames can be assembled to a realistic multi-trace scope movie

    New RF systems for the SUPER-SPS and SUPER-IRS

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    The RF system requirements necessary to fulfil the desired specifications for a possible new set of LHC injectors and the consequent technical implications are examined

    SPLinac: Computer Simulations of SC Linac RF Systems with Beam

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    The beam in a proton linac is very sensitive to field perturbations in the cavities. Therefore a simulation program was written modeling longitudinal beam dynamics in a realistic composite linac RF system. Fast RF vector sum feedback loops control several cavities with b-dependent transit time factors driven by one transmitter. Modeling of feedback loops covers limited transmitter power and bandwidth and possible loop-delay. Vector sum calibration errors, power splitting errors and scatter in the coupling strength to the cavities are optional as well as beam loading of the pulsing beam. Different modes of mechanical cavity perturbations including Lorentz force detuning can be chosen. A multitude of phase-space representation of bunches as well as RF quantity plots are available, most of them can be assembled as a movie, showing the system dynamics in 'real time'

    Digital Generation of Noise-Signals with Arbitrary Constant or Time-Varying Spectra (A noise generation software package and its application)

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    Artificial creation of arbitrary noise signals is used in accelerator physics to reproduce a measured perturbation spectrum for simulations but also to generate real-time shaped noise spectra for controlled emittance blow-up giving tailored properties to the final bunch shape. It is demonstrated here how one can produce numerically what is, for all practical purposes, an unlimited quantity of non-periodic noise data having any predefined spectral density. This spectral density may be constant or varying with time. The noise output never repeats and has excellent statistical properties, important for very long-term applications. It is difficult to obtain such flexibility and spectral cleanliness using analogue techniques. This algorithm was applied both in computer simulations of bunch behaviour in the presence of RF noise in the PS, SPS and LHC and also to generate real-time noise, tracking the synchrotron frequency change during the energy ramp of the SPS and producing controlled longitudinal emittance blow-up. This successful experience indicates that this method can also be applied in the LHC

    The LEP2 Superconducting RF System

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    The LEP2 superconducting RF system supplies at present about 2600 MV per turn to the electrons and positrons of the LEP beams, giving a beam energy largely above 90 GeV to create the desired massive W ±-pairs for physics. It is by far the largest such system world wide and a further upgrade is still under way to increase the W± production rate and cover new physics grounds. More than 10 MW RF power were routinely transmitted to the beam during last year's smooth operation. We will cover on the technical parts of this system: the cavities, couplers, tuners, cryostats, the cryogenics and the RF ge neration and distribution. We will also report on operational experience and future plans

    Adaptive RF Transient Reduction for HIGH Intensity Beams with Gaps

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    When a high-intensity beam with bunch-trains and gaps passes a cavity with a high-gain vector feedback enforcing a constant voltage, large transients appear, stressing the RF high power hardware and increasing the trip rate. By modulating the cavity voltage with a varying periodic waveform (set-function), the RF power can be made constant while still preserving the high feedback gain. The average cavity voltage is conserved but bunches have to settle at slightly shifted positions. A method is derived to obtain this set-function in practice while making no assumptions or measurements of the beam or RF parameters. Adiabatic iterations are made including the whole machine as an analog computing device, using all parameters as they are. A computer simulation shows the success of the method

    Technological aspects of crab cavities

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    Some technical aspects of a crab cavity system with respect to an application in LHC are described

    Control Instabilities in a Pulsed Multi-Cavity RF System with Vector Sum Feedback (A Mathematical Analysis) 052

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    Upcoming projects relying on pulsed linear accelerators intend to use superconducting RF systems. Cost reasons suggest driving several cavities by a common transmitter, controlled over a vector sum feedback system, possibly supported by a feed forward system. Numerical simulations hint that such a system may become uncontrollable under certain conditions. In the present paper, for a model very close to reality, we will present a mathematical proof that in fact spontaneous symmetry braking is possible for these configurations, defining also the precise conditions under which it will take place. These can be used as an estimate for the real RF system stability limits. The listing of a small program demonstrating the mechanism numerically for two cavities is attached
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