The Accumulator subnode is available from the context menu (right-click the Collisions parent node) or from the Physics toolbar, Attributes menu. Each Accumulator subnode defines a variable, called the accumulated variable, in the domains where the parent Collisions node is applied. Whenever a particle collides with a background gas molecule, the value of the accumulated variable in that element is incremented based on the value of the user-defined Source term R for the particle.

Select an option from the Accumulator type list: Density (default) or Count.

Enter the Accumulated variable name. The default is rpc. The accumulated variable is defined as <scope>.<name>, where <scope> includes the name of the physics interface node, parent Collisions node, and the Accumulator node; and <name> is the accumulated variable name.

For example, if the Accumulator subnode is added to a Collisions node in an instance of the Charged Particle Tracing interface using the default variable name rpc, the accumulated variable name might be cpt.col1.clacc1.rpc.

Select an option from the Collision types to accumulate list. The default is All, or you could select any other subnode to the parent Collisions node from the list. Change this setting, for example, if you only want to compute the number density of elastic collisions while ignoring charge exchange reactions.

Enter a Source R. The unit of the source term depends on the settings in the Units section. Whenever a collision occurs, the accumulated variable is incremented by the source term in the mesh element the particle occupies. If the Accumulator type is set to Density, the source term is divided by the volume of the element (in 3D) or area of the element (in 2D).

Select a Dependent variable quantity from the list; the default is Dimensionless [1]. To enter a unit, select None from the list and in the Unit field enter a value, for example, K, m/s, or mol/m^3.