How to use it? Basically, given a fieldmap for an RF structure, the time-dependent fields are E(x,y,z,t) = maxGradient * Eo(x,y,z) * sin(ω(t – timeOffset)) B(x,y,z,t) = maxGradient * Bo(x,y,z) * -cos(ω(t – timeOffset)) timeOffset contains the RF phase phaseAcc. If two of three (timeOffset or phaseAcc, maxGradient, and a fixed output) are specified, pillbox will determine the missing quantities, if possible. An overdefined system is reported as an error. The timingMethod specifies how to find timeOffset; the default is atZ (set time of arrival) to emulate the old pillbox, while maxE (find maximum energy gain) is more typical of how cavities are actually timed. For example, an RF cavity might follow an absorber in a cooling channel with a maximum peak field, and so be asked to find the appropriate phase: pillbox RF1 … maxGradient=20 timingMethod=maxE fixMomentum=200 or given the phase to find the appropriate voltage pillbox RF2 … timingMethod=maxE fixMomentum=200 phaseAcc=45 or the phase and voltage could be set, and 0 o RF determined pillbox RF3 … timingMethod=maxE maxGradient=20 phaseAcc=45 or fix everything pillbox RF4 … maxGradient=20 timeOffset= Note that the fixed value is at the atZlocal location, not necessarily the exit. IMPROVEMENTS TO THE G4BEAMLINE PILLBOX * * K.B. Beard 1#, S.A. Bogacz 2, V.S. Morozov 2, T.J. Roberts 1, Y.R. Rob lin 2 1 Muons Inc, 2 Jefferson Lab What was changed? Basically, the pillbox was rewritten with new options, but is 100% compatible with previous versions except that phaseAcc no longer defaults to 40 o (50 o before crest for a positive particle). G4beamline defines 0 o to be the zero crossing on the rising slope of the E field. New options: timingMethod Method for determining the nominal timeOffset {atZ, maxE, noE, minE, maxT, nomT, minT, maxX, noX, minX, maxY, noY, minY}. timingAtZ Local Z location for timing (mm). fixMomentum Specify total output momentum (MeV/c). fixEnergyGain Specify energy gain (MeV). fixTransitTime Specify transit time (ns). fixXdeflection Specify local output XZ angle (deg). fixYdeflection Specify local output YZ angle (deg). fixTolerance Specify allowable error on fixed settings [1.e-3]. timingDisplay Set nonzero to show timing volume and print info messages References [1] [2] Thomas J. Roberts et al., G4Beamline particle tracking in matter-dominated beam lines. In Proceedings of EPAC08, Genoa, Italy [484]. [3] Geant4 – Muons, Inc. Acknowledgements *Supported in part by US DOE STTR Grant DE-FG02-08ER m ABSTRACT G4beamline 1,2 is a powerful, flexible, user-friendly, and OpenSource tool for using the Geant4 library 3 to simulate many systems of interest. In particular, it has an many enhancements to aid in the modelling of particle accelerators. Its pillbox, used to model an RF cavity, is being extended to allow it to model multi-cell and transverse-mode cavities and to allow better tuning of those structures. Why? The old pillbox didn’t: handle multicavity structures gracefully phase particles with β<<1 very well. phase deflecting cavities at all locally adjust gradients A pillbox is a roughly cylindrical container – the RF fields are inside the container. The timingVolume is just a region within the pillbox used to determine the timing of the RF, if needed. It usually extends from the entrance of the pillbox to either the center (timingMethod=atZ) or to the exit all other methods). time of arrival min Y deflection max energy gain ; logic flow