Voronoi Particle Merging Algorithm for PIC Codes

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

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

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

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)

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

Technological aspects of crab cavities

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

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

Simulation of the SPL SC RF system with Beam using "SPLinac"

The study of an H- linac with superconducting RF at CERN, called SPL, requires examination of microphonics and Lorentz detuning of the superconducting cavities and their influence on the beam quality at the and of the linac. We report here on first studies using the program 'SPLinac