# Slab Settable Flux Emitter¶

All particle types may emit from a slab settable flux emitter. Certain emission specifications are only available based on particle type and particle weights specification. Available in all coordinate simulations.

start time

Time to start emitting particles in seconds.

stop time

Time to stop emitting particles in seconds.

emission specification

Specification of the emitted particles, note that the specification options vary for constant or variable/managed weight particles.

• emission current density

emission current density Specify the current density of the emitter (amps/meter^2). Can be a spatial profile.

velocity coordinate system Either global or surface. A global coordinate system will specify the emission velocities according to global axis. A surface coordinate system will set the emission directions according to the normal of the emission object. So in a surface coordinate system a lower simulation bounds the emission velocity must be negative to emit into the simulation space, for an upper simulation boundary the particles must be positive to emit into the simulation space.

• average velocity 0: The average (mean) speed of particles in the x-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for the direction normal to the emitting surface.

• average velocity 1: The average (mean) speed of particles in the y-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• average velocity 2: The average (mean) speed of particles in the z-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• thermal velocity 0: A spread (standard deviation) for particle speeds in the 0 direction.

• thermal velocity 1: A spread (standard deviation) for particle speeds in the 1 direction.

• thermal velocity 2: A spread (standard deviation) for particle speeds in the 2 direction.

• emission flux

emission flux Specify the flux of the emitter (particles/meter^2). Can be a spatial profile.

velocity coordinate system Either global or surface. A global coordinate system will specify the emission velocities according to global axis. A surface coordinate system will set the emission directions according to the normal of the emission surface. So in a surface coordinate system a lower simulation bounds the emission velocity must be negative to emit into the simulation space, for an upper simulation boundary the particles must be positive to emit into the simulation space.

• average velocity 0: The average (mean) speed of particles in the x-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for the direction normal to the emitting surface.

• average velocity 1: The average (mean) speed of particles in the y-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• average velocity 2: The average (mean) speed of particles in the z-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• thermal velocity 0: A spread (standard deviation) for particle speeds in the 0 direction.

• thermal velocity 1: A spread (standard deviation) for particle speeds in the 1 direction.

• thermal velocity 2: A spread (standard deviation) for particle speeds in the 2 direction.

• emission current

emission current Specify the total emitted current per second from the emitter (amps/second).

velocity coordinate system Either global or surface. A global coordinate system will specify the emission velocities according to global axis. A surface coordinate system will set the emission directions according to the normal of the emission surface. So in a surface coordinate system a lower simulation bounds the emission velocity must be negative to emit into the simulation space, for an upper simulation boundary the particles must be positive to emit into the simulation space.

• average velocity 0: The average (mean) speed of particles in the x-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for the direction normal to the emitting surface.

• average velocity 1: The average (mean) speed of particles in the y-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• average velocity 2: The average (mean) speed of particles in the z-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• thermal velocity 0: A spread (standard deviation) for particle speeds in the 0 direction.

• thermal velocity 1: A spread (standard deviation) for particle speeds in the 1 direction.

• thermal velocity 2: A spread (standard deviation) for particle speeds in the 2 direction.

• emission rate

emission rate Specify the total number of particles emitted per second (particles/second)

velocity coordinate system Either global or surface. A global coordinate system will specify the emission velocities according to global axis. A surface coordinate system will set the emission directions according to the normal of the emission surface. So in a surface coordinate system a lower simulation bounds the emission velocity must be negative to emit into the simulation space, for an upper simulation boundary the particles must be positive to emit into the simulation space.

• average velocity 0: The average (mean) speed of particles in the x-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for the direction normal to the emitting surface.

• average velocity 1: The average (mean) speed of particles in the y-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• average velocity 2: The average (mean) speed of particles in the z-direction when velocity coordinate system is set to “global”. If set to “surface” then this will be the average velocity for a direction perpendicular to the emitting surface.

• thermal velocity 0: A spread (standard deviation) for particle speeds in the 0 direction.

• thermal velocity 1: A spread (standard deviation) for particle speeds in the 1 direction.

• thermal velocity 2: A spread (standard deviation) for particle speeds in the 2 direction.

• Fowler Nordheim Emission

Specify particle emission according to the Fowler-Nordheim model. Only available with variable/managed weight electron particle species.

work function [eV]: Work function of the material from which emission is occurring.

A: Coefficient A of the Fowler-Nordheim emission model.

B: Coefficient B of the Fowler-Nordheim emission model.

field enhancement: Multiplies the measured electric field by this amount.

Cv: Coefficient Cv of the Fowler-Nordheim emission model.

Cy: Coefficient Cy of the Fowler-Nordheim emission model

• Richardson Dushman Emission

Specify particle emission according to the Richardson-Dushman model. Only available with variable/managed weight electron particle species.

work function [eV]: Work function of the material from which emission is occurring. Parameter in the Richardson-Dushman model.

field evaluation offset:

temperature (K): Temperature of the material from which emission is occurring. Parameter in the Richardson-Dushman model.

field enhancement: Multiplies the measured electric field by this amount.

flux multiplier: Multiplies the resulting output current by this amount.

• Child Langmuir Emission

Specify particle emission according to the Child Langmuir model. Only available with variable/managed weight electron particle species.

• space charge limited emission: This will limit the current to provide a more consistent emission current, providing higher accuracy particularly in explosive emission cases, such as a pulsed power magnetron. For non pulsed-power simulations it is not necessary.

• average velocity 0: The average (mean) speed of particles in the 0 direction.

• average velocity 1: The average (mean) speed of particles in the 1 direction.

• average velocity 2: The average (mean) speed of particles in the 2 direction.

• thermal velocity 0: A spread (standard deviation) for particle speeds in the 0 direction.

• thermal velocity 1: A spread (standard deviation) for particle speeds in the 1 direction.

• thermal velocity 2: A spread (standard deviation) for particle speeds in the 2 direction.

emission surface
• lower x

The lower x simulation boundary.

• lower y

The lower y simulation boundary.

• lower z

The lower z simulation boundary.

• upper x

The upper x simulation boundary.

• upper y

The upper y simulation boundary.

• upper z

The upper z simulation boundary.

emission offset

The distance away from the object that emitted particles are placed, as a fraction of a cell length.

macroparticle emission

Only available with variable/managed weight particles. This allows for the specification of the macroparticle emission independent of the emitted particles. Used to handle computational concerns around macroparticle weight.

macroparticle rate

Number of macroparticles to emit per timestep. This value can be modified by the macroparticle emission profile.

macroparticle emission profile

Spatial profile for emission of the macroparticles. If this corresponded to half of the emissions shape, half of the number of macroparticles specified in macroparticle rate would be emitted, while the emission specification would be unaffected.

NOTE: To allow the user to emit from non-Maxwellian probability distribution functions, one can import a Python SpaceTimeFunctions. The easiest way to do this is to right-click with your mouse on the component of the mean velocity you wish to emit (for example mean velocity 0) then click on Assign SpaceTimeFunction and finally choose the python SpaceTimeFunction you have already defined. It is best not to mix this method with the default method of choosing the velocity from a Maxwellian. Therefore, when you write your python SpaceTimeFunction, include all drift- and thermal-velocity terms in the Python function. Then leave the thermal velocity 0 option set to 0.0. Also, all three components are independent. So if your python function depends only on component 0, then you could treat the other two components as Maxwellian and fill in the mean velocity and thermal velocity options using the methods discussed above for components 1 and 2.