Beam-Beam Interactions

The command BEAMBEAM may be inserted in a beam line to simulate a beam-beam interaction point:

label:BEAMBEAM,TYPE=string,APERTURE=real-vector,
      SIGX=real,SIGY=real,XMA=real,YMA=real,CHARGE=real;

The code for this element has been contributed by J.M. Veuillen (1987), and has been adapted to C++ in 1997. It has six real attributes:

SIGX

The horizontal extent (standard deviation) of the opposite beam (default: 0 m).

SIGY

The vertical extent (standard deviation) of the opposite beam (default: 0 m).

XMA

The horizontal displacement of the opposite beam with respect to the ideal orbit (default: 0 m).

YMA

The vertical displacement of the opposite beam with respect to the ideal orbit (default: 0 m).

CHARGE

The charge of particles in the opposite beam in proton charges (default: 0).

NPART

The number of particles in the opposite beam. (default: 0).

A beam-beam element requires the particle momentum P and its charge CHARGE to be defined on the relevant optics command before any calculations are performed.

Example:

BEAM,MOMENTUM=46.0,MASS=PMASS,CHARGE=1.0;
BB:BEAMBEAM,SIGX=1.E-3,SIGY=5.E-4,CHARGE=1.0,NPART=1.0E12;

A three-dimensional representation of a beam-beam interaction is available with the command

label:BEAMINT,TYPE=string,APERTURE=real-vector,
      PHI=real,NSLI=integer,FAST=bool,XIYN=real,DX=real,DY=real,DZ=real,
      BETXS=real,BETYS=real,ALFXS=real,ALFYS=real,
      DXS=real,DPXS=real,DYS=real,DPYS=real,
      EXS=real,EYS=real,SIGTS=real,SIGES=real;

Its parameters are:

PHI

Horizontal crossing angle.

NSLI

Number of slices to be taken in strong beam.

FAST

If true, use tables for computing the error function.

XIYN

Beam-beam parameter.

DX

Horizontal displacement of the interaction point in [m].

DY

Vertical displacement of the interaction point in [m].

DZ

Longitudinal displacement of the interaction point in [m].

The following parameters describe the strong beam:

BETXS

Horizontal $\beta*$ in [m].

BETYS

Vertical $\beta*$ in [m].

ALFXS

Horizontal $\alpha*$* in [1].

ALFYS

Vertical $\alpha*$ in [1].

DXS

Horizontal dispersion in [m].

DPXS

Horizontal dispersion slope in [m].

DYS

Vertical dispersion in [m].

DPYS

Vertical dispersion slope in [m].

EXS

Horizontal emittance in [m rad].

EYS

Vertical emittance in [m rad].

SIGTS

Bunch length in [m].

SIGES

Energy spread in [1].