Particle Beam

Simulation: Sources and LoadsParticle Beam

Particle beams are the driving sources for the wakefield solver. This type of source defines a bunch of charged particles, which enters the calculation domain at a certain position and propagates with a constant velocity on a straight line parallel to a coordinate axis through the structure. You will need at least one particle beam source, before starting a wakefield simulation run. The charge distribution over the spacial parameter s can be described as follows:

Gaussian beam properties

Sigma
Defines the standard deviation of the Gaussian shaped bunch.

Velocity (beta)
Sets the velocity of charged beam particles. Beta can be chosen between 0 and 1. V = C0 * beta

Charge
Specifies the total charge of the Gaussian shaped bunch.

 

Current injection scheme

For ultra-relativistic beams (beta > 0.999) two beam injection schemes are available:

 

Scheme

Description

Analytic

This scheme integrates the Gaussian charge distribution very accurate at each time-step and computes the resulting current. Its advantage is that the current created by the travelling bunch is modeled very accurately. The disadvantage is that non-physical longitudinal electric fields appear due to numerical dispersion effects. This might affect the wake computation if the grid is too coarse.

Transmission line

This algorithm creates a current injection which is equal to a current traveling on a PEC wire. The advantage of this approach is that non-physical longitudinal electric fields are not created which improves the quality of the wake potential. Its disadvantage is, that current "reflections" appear if the grid is not homogeneous in longitudinal direction.

 

For beams with a beta value below 0.999 the "Analytic" scheme is always used.

 

Mesh settings

Consider for mesh refinement

Determine if the beam properties (Sigma and Velocity) should have an influence on the mesh refinement. If one chooses to consider the beam for a mesh refinement (which is strongly recommended) a maximum beam frequency is computed from Sigma and the velocity, which is used for the mesh refinement.

 

Lines per sigma

If activated, this setting allows to control the longitudinal mesh refinement of the particle beam. If the numerical dispersion effects plays an important role it is possible to decrease this type of error by increasing the lines per sigma.

 

Beam location

Global Beam direction
Specify the global beam direction. It is only possible to define beams parallel or antiparallel to a main coordinate (X Y Z).

Use Pick
If a pickpoint is available one can choose if the pickpoint is taken to define a point on the beam axis, or if the X/Y/Z edit fields are used.

X/Y/Z
Specify a point on the beams axis by entering its coordinates numerically.

Wakefields...

Opens the Wakefield calculation dialog box where one can specify how to compute wakefields.

OK

Performs your settings and leaves the dialog box.

Cancel

Closes this dialog box without performing any further action.

Help

Shows this help text.

See also

Wakefield Solver Overview, Wakefield Solver, Wakefield Calculation