childLangmuirVelGenVelocity generator that determines the weight of the particles (and therefore the current) based on the Child-Langmuir Law. The current is simply calculated to vary linearly with the normal \(E\) field. Ampere’s law is solved, recognising that this represents the case where at the nearby virtual cathode surface \(E=0\), as this represents the potential minimum.
reduction (option)The factor by which emitted current is reduced. e.g. if reduction = 0.1 then you emit 1/10 the child-langmuir current. Reduction = 1.0 is the full child-langmuir current
STFunc (block, option)STFunc Block with function name specifying component#, where ‘#’ is the component number (0,1,2, …) for each velocity component you wish to specify.
The component# space-time function blocks are specified like any other Vorpal space-time function block, and the value of this function (depending on the position and time of the particle’s placement at load or emission time) is used to determine the value of the specified component of the velocity.
<VelocityGenerator emitVelGen>
kind = childLangmuirVelGen
reduction = 0.1 #1.0e-3
# Optionally set individual components of the velocity with STFunc blocks
<STFunc component0>
kind = expression
expression = -2.0e5
</STFunc>
</VelocityGenerator>