Particle Properties
Use the Particle Properties node to specify the particle mass and charge number when using the Newtonian or Newtonian, first order formulation. Specify the particle velocity when using the Massless formulation.
Particle Species
This section is shown when Newtonian or Newtonian, first order is selected as the Formulation. Choose an option from the Particle species list. The default is User defined, allowing the mass and charge number to be specified directly. The remaining options are detailed in Table 4-2. The values in the Mass column show the numeric values of the particle mass, as well as any built-in physical quantities for the masses of these species.
 
Table 4-2: Built-in Species for Charged Particle Tracing.
Name
Mass (kg)
Charge Number
Electron
me_const = 9.10938356 × 10−31
 -1
Proton
mp_const = 1.672621898 × 10−27
 +1
Neutron
mn_const = 1.674927471 × 10−27
 0
Alpha particle
 6.6446573357 × 10−27
 +2
Positron
me_const = 9.10938356 × 10−31
 +1
Particle Mass
This section is shown when Newtonian or Newtonian, first order is selected as the Formulation and User defined is selected from the Particle species list.
Enter a value or expression for the Particle mass mp (SI unit: kg). The default expression is me_const, which is a predefined constant within COMSOL Multiphysics for the electron mass, 9.10938356 × 10−31 kg.
If the Relativistic correction checkbox is selected in the physics interface Advanced Settings section, instead specify the Particle rest mass mr (SI unit: kg). The default expression is me_const.
Charge Number
This section is shown when Newtonian or Newtonian, first order is selected as the Formulation and User defined is selected from the Particle species list.
Enter a value for the Charge number Z (dimensionless). The default is −1 corresponding to the charge number of an electron.
Particle Velocity
This section is shown when Massless is selected as the Formulation.
Enter a vector for the Particle velocity v (SI unit: m/s) based on space dimension. The Massless formulation means that the particles follow streamlines of the particle velocity expression.
 
The Particle Properties node is a default feature for all particle tracing physics interfaces. This default node cannot be deleted or disabled, and it is not possible to paste or duplicate this node in the model builder.
However it is possible to add more than one instance of this Particle Properties node to the same model. When you do so, each instance corresponds to a different species of particle. For example, two Particle Properties nodes could represent ions and electrons, or white blood cells and bacteria. Unlike the default Particle Properties node, these nondefault nodes can be deleted, disabled, duplicated or pasted in the model builder.
When two or more species are in the same model, you can decide which species is released by each particle release feature, such as the Release, Inlet, or Release from Grid feature. To do so, select the appropriate Particle Properties node from the Released particle properties list in the physics feature Released Particle Properties section.
For more information, see Particle Tracing with Multiple Species in the Particle Tracing Modeling chapter.