Post-processing with acdtool¶

ParaView shows field patterns. For numbers such as shunt impedance, kick factor, and peak surface fields, use the RF post-processor built into acdtool:

acdtool postprocess rf <project>.rfpost

It runs serially and reads the mode files that Omega3P or S3P wrote. Running it with no file argument writes a sample.rfpost template containing every available function with default values, which is the easiest way to start.

The .rfpost file¶

The file is a sequence of named blocks. The first must be RFField, which selects the mode and sets scaling. Every other block is a calculation that is enabled with ionoff = 1.

pillbox-rtop.rfpost

RFField
{
   ResultDir   = omega3p_results   // where the .mod files are
   FreqScanID  = 0                 // S3P only: frequency scan index
   ModeID      = 0                 // which mode, when a block uses modeID = -1
   xsymmetry   = magnetic          // [none, electric, magnetic]
   ysymmetry   = magnetic
   gradient    = 2.0e7             // V/m; -1 keeps normalized fields
   cavityBeta  = 1.0               // particle beta for V and R/Q integrals
   reversePowerFlow = 0            // [1 = charging, 0 = decaying]
   x0 = 0.0                        // integration axis x
   y0 = 0.0                        // integration axis y
   gz1 = -0.057                    // integration start z, m
   gz2 =  0.057                    // integration end z, m
   npoint = 300                    // points along the axis
   fmnx = 10                       // field map resolution
   fmny = 10
   fmnz = 50
}

RoverQ
{
   ionoff = 1
   modeID1 = -1                    // -1, -1: all modes
   modeID2 = -1
   x1 = 0.0
   x2 = 0.0
   y1 = 0.001
   y2 = 0.001
   z1 = 1e8                        // 1e8: use the model bounding box
   z2 = 1e8
}

maxFieldsOnSurface
{
   ionoff = 1
   surfaceID = 6
}

RFField keys¶

Key	Meaning
`ResultDir`	Results directory from the solver
`ModeID`	Mode used by single-mode functions
`xsymmetry`, `ysymmetry`	Tell the post-processor which symmetry planes were used so volume integrals are scaled to the full cavity
`gradient`	Accelerating gradient in V/m used to scale fields. With `-1`, fields keep the solver's normalization of 1 J stored energy.
`cavityBeta`	Particle velocity for the transit-time factor in V and R/Q
`gz1`, `gz2`	Axial integration range for the voltage. Set to the cavity length, not the whole beam pipe, to define the gradient consistently.

Functions¶

Block	Computes
`RoverQ`	Voltage along a line and R/Q = V²/(ωU) per mode
`RoverQT`	Transverse R/Q
`kickFactor`	Transverse kick factor
`FieldMap`	Field on a 3D grid of nx × ny × nz points in the given box
`FieldAtPoint`, `ALLFieldAtPoint`	Field at one point, for one or all modes
`FieldOnLine`, `ALLFieldOnLine`	Field along a line with `npoint` samples at a given `rfphase`, written to `filename`
`fieldOn2DBoundary`	Field on a boundary surface, written to file
`fieldOnSurface`	Field on a surface as components or amplitude
`maxFieldsOnSurface`	Peak E and H on a surface with their locations
Multipole analysis	Multipole decomposition of the field on axis

Coordinates are in meters. A coordinate of 1e8 means "use the bounding box of the model," which is convenient for line integrals along the full axis.

Output¶

acdtool writes to standard output and to rfpost.out. It begins with a mode summary:

** Omega3P/S3P Mode Summary:
**   Total number of modes :      2
**      ModeID         Frequency(r,i)                       Qext
**         0           1.31381e+09, 0.00000e+00           0.00000e+00
**         1           2.32914e+09, 0.00000e+00           0.00000e+00
**   Model bounding box: ( 0.00000e+00,  0.00000e+00 -1.50000e-01)
**                       ( 1.00005e-01,  1.00123e-01  1.50000e-01)

followed by a [scaling] block giving the voltage and the factor used to scale the normalized fields to the requested gradient, then one block per enabled function:

[RoverQ]
{  // RoverQ=V^2/(omega*U)
 ModeID  Frequency           (V_r, V_i)                      |V|            RoQ(ohm/cavity)
    0   1.31381e+09  ( 2.2980e+00,  3.4925e+00)    4.18073e+00      1.19567e+02
    1   2.32914e+09  (-7.2671e-04,  6.2729e-04)    9.59998e-04      3.55621e-06
}

[maxFieldsOnSurface]
{
   surfaceID :   6
      ModeID :   0
        Emax :  4.22488e+07 (V/m)   at ( 3.9627e-02,  1.8486e-02, -4.5454e-02)
        Hmax :  5.80786e+04 (A/m)   at ( 3.3116e-02,  7.9193e-02,  3.2771e-02)
}

Surface field values correspond to the gradient in RFField. The ratio E_peak/E_acc is a standard figure of merit and comes straight from Emax divided by gradient.

R/Q convention

acdtool reports R/Q in the circuit convention V²/(ωU) in ohms per cavity, where V is the full on-axis voltage after the transit-time factor. For a symmetric model the xsymmetry and ysymmetry settings restore the full-cavity stored energy. Divide by 2 for the linac convention if your comparison uses it.

S3P results¶

The same tool works on S3P output. Set FreqScanID to pick a frequency point from the scan and ModeID to pick the excited port mode.