Abstracts Brochure - CERN

WEPCH124
WEPCH125
WEPCH126
28-Jun-06 16:00 - 18:00 WEPCH — Poster Session
BDSIM - Beamline Simulation Toolkit Based on Geant4
I.V. Agapov, G.A. Blair, J. Carter (Royal Holloway, University of
London)
308
BDSIM is a code that combines acceleratorstyle
particle tracking with traditional Geantstyle
tracking based on Runge-Kutta techniques.
This approach means that particle
beams can be tracked efficiently when inside the beampipe, while also enabling full Geant-4 processes when beamparticles
interact with beamline apertures. Tracking of the resulting secondary particles is automatic. The code is
described, including a new MAD-style interface and new geometry description, and key performance parameters are
listed.
New Design Tools for a Cyclotron Central Region
D. Battaglia, L. Calabretta, D. Campo, M.M. Maggiore, L.A.C. Piazza,
D. Rifuggiato (INFN/LNS)
A code allowing to design the spiral inflector
and the central region of the SCENT cyclotron
was implemented. The code uses the
main equations of motion of a particle in an
electromagnetic field and provides a useful interface to describe the geometry and the physical constraints of the inflector
and central region complex to be simulated. In particular only the main parameters of the inflector, of injected
beam and of magnetic field are needed to calculate the profile of the inflector, which is then used to build a model
that can be imported in all magnetic simulators, like Vector field OPERA, and in any standard CAD. An application
interface allows one to find the emittance and the particles’ distributions outside the inflector. An iteration process
to design the central region was also developed. The distributions of electric and magnetic field of the model were
achieved by OPERA 3D but a simplified version using OPERA 2D is also included. The flowchart of the code, its
interface and results of our simulations will be presented.
Issues in Modelling of Negative Ion Extraction
In the context of negative ion sources pro-
M. Cavenago (INFN/LNL) V. Antoni, F. Sattin (CNR/RFX) posed for neutral beam injectors for tokamaks,
halo of the extracted beam is typically
large (about 10 %) and optimum shape of the multiaperture extraction electrode is a matter of research. Present
designs range from an aperture angle of 45 degree (low current, convergent beam) to 90 degrees (flat electrode, high
current, large divergence and halo). Two major difficulties of the beam extraction modelling are here discussed. First,
the generation processes of negative ion show some shortcomings: volume production seems low; wall production
is large, but ions have wrong directions and/or large nonuniformity in current density; elastic scattering of wall
generated ions into the extraction direction must compete with mutual neutralization. Second, the plasma sheath
charge has to be negative on the extraction hole surface and positive on the nearby wall surface, which enhances
beam aberration near hole edge. After discussing limitation of existing codes and model, result from an ad hoc
code are discussed. Also 2D equation for the selfconsistent electrostatic field can be written and implemented into a
multiphysics general purpose program.