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5.6.6. Parameter Reference

Parameter Name

Valid Entries

Description

Field Sweep/RF Input File

Selected from imported file list.

The path to the field archive that will be used in the particle simulation.

Field Sweep/Phase Increment [PHASE]

Real number ≥ 0.0

Primary particle emission occurs over the first complete RF period, and the phase increment between emissions is equal to this value.

Field Sweep/Number of RF Periods

Real number > 0.0

Sets the maximum temporal length of the simulation (in RF periods). All particles are tracked from when they are emitted until either they are removed due to phasing, yield, or other criteria, or until a maximum time given by this variable multiplied by the RF period.

Field Sweep/Normalization Target

Peak Surface E-Field Magnitude, Peak E-Field Magnitude, Peak Axial E-Field On Axis Magnitude, Average Accelerating E-Field Magnitude

The solver will use the specified field to normalize field magnitude(s) used in the analysis. The axis is defined by the shunt integration path set in the OM3p/OM2p field analysis, or is the x-axis if a driven frequency field analysis was used.

Field Sweep/Magnitudes/Specification

Linear Range Count, Linear Range Increment, “Custom List Specification”

Determines how the field amplitudes are specified.

Particle Tracker/Method

Runge Kutta, Backward Difference, Quadratic Fit

Integration method used by the Particle Tracker.

Particle Tracker/Maximum Track Time [TIME]

Real number > 0.0

Total time period for which the Particle Tracker follows a particle.

Particle Tracker/Report Errors

True, False

If true, report errors from the Particle Tracker to the Log.

Particle Tracker/Runge Kutta/Number of Time Steps Per Element

Integer > 0

Visible if Particle Tracker/Method is "Runge Kutta". Number of times per element that particle's position is computed. Higher numbers give more accurate calculations and longer run times.

Particle Tracker/Runge Kutta/Integration Order

2 or 4

Visible if Particle Tracker/Method is "Runge Kutta". Integration order for the Runge Kutta particle tracker.

Particle Tracker/Backward Difference/Number of Time Steps Per Element

Integer > 0

Visible if Particle Tracker/Method is "Backward Difference". Number of times per element that particle's position is computed. Higher numbers give more accurate calculations and longer run times.

Particle Tracker/Backward Difference/Integration Order

2≤ order ≤10

Visible if Particle Tracker/Method is "Backward Difference". Integration order for the backward difference particle tracker.

Bias Field/Uniform Electric Field [ELECTRIC FIELD]

Three comma-delimited real numbers.

This entry is used to specify a spatially invariant static electric field that is added to the field that has been read in from file. Specified as a 3-vector in V/m.

Bias Field/Uniform Magnetic Field [MAGNETIC FIELD]

Three comma-delimited real numbers.

This entry is used to specify a spatially invariant static magnetic field that is added to other static and time-varying magnetic fields. Specified as a 3-vector in A/m.

Particle Output/Orbits

Only Resonant Particles With Yield > 1, All Resonant Particles, None

"None": no particle orbits are output, and no individual particle statistics table is generated. "All Resonant Particles": all particles that survive to the specified number of impacts are output, irrespective of yield (provided that they are not terminated due to the cumulative yield floor test). "Only Resonant Particles With Yield > 1": Only output resonant particle orbits that show a net gain (cumulative yield greater than unity) over the requisite number of impacts.

Particle Output/Snapshots

True, False

If true, compute and output time-domain snapshots of the particle locations.

Particle Resonance Requirements/Cumulative Yield Floor

Real number ≥ 0.0

This value is used to terminate particles that have small yields. Any particle that reaches a cumulative yield below the yield floor is terminated.

Particle Resonance Requirements/Minimum Number of Impacts

Integer > 0

The number of times that a particle impacts the structure and is re-emitted as a secondary before it is considered to have a "resonant" orbit.

Particle Resonance Requirements/Temporal Spacing Between Impacts

RF Period Fraction, 0 = Disable

This value can be used to screen particles for particular orbit characteristics. In particular, setting this value to something other than zero (the default) requires the spacing between impacts given by the specified fraction of an RF period. For example, if this value is set to 0.5, only half-period resonances are allowed, and particles with a temporal spacing between impacts of other than this value are terminated.

Primary Emission Control/Number of Particles to Emit From Each Vacuum Element Volume

Integer ≥ 0

Sets the number of particles to be initiated from each volume element. If this parameter is set to 0 (the default value) no particles are initiated within the volume elements and a surface emission model is used through the application of an Emitter boundary condition. Else, particles are created with random locations and velocities within each element. Most particles will terminate on the first surface they impact yielding no secondary particles. Some, however, impact with a favorable combination of energy and field amplitude/phase such that one or more secondary particles are emitted, providing the opportunity for a multipacting resonance to occur. Thus it is important that this value be set high enough to produce an initial particle population that is dense enough to identify resonances, but not so large that the simulation requires an inordinate amount of time to complete. The best strategy is to make several runs with increasing values until the predicted multipacting bands stop changing.

Primary Emission Control/Number of Particles to Emit From Each Element Face on Metal Boundaries

Integer ≥ 0

Particles may be initiated from surfaces as well as, or instead of, the volume, and this parameter sets the number of particles to be emitted from each boundary element face. This control does not affect secondary emission or field emission, and instead is used only to control particle initiation from structure boundaries. See discussion on volume initiation above for additional considerations.

Primary Emission Control/Maximum Number of Particles to Emit From Any Element Face

Integer ≥ 0

Sets a ceiling on the number of particles emitted.

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