The OPAL Discussion Forum

[Christopher Pierce <cmpierce AT uchicago.edu>]

Hey folks,

First, I have recently started using opal and wanted to thank you for it. It looks like it will be very useful for my research.

I am emailing because I am running into a problem with the attached input file. It is supposed to represent a beam in a artificial electrostatic focusing channel. I do this by loading a fieldmap into the simulation with a constant negative radially pointing E-field and no Ez component.

The problem I encounter is that after loading the input file, the program returns the error "quaternion isn't unit quaternion. Norm: -nan". 

I found out that I can make the error go away by setting a single element of the fieldmap to have finite Ez (also attaching the file as "e-lens-fixed.T7". This fieldmap seems to give me the results I expect. Is there something that I am doing wrong here?

Cheers,

Chris Pierce

OPTION, PSDUMPFREQ = 300;   // 6d data written every 300 time steps (h5).
OPTION, STATDUMPFREQ = 10;  // Beam Stats written every 10 time steps (stat).
OPTION, BOUNDPDESTROYFQ=10; // Delete lost particles, if any
OPTION, VERSION = 20300;  // This indicates that it works with an OPAL 
version of 2.3

Title, string="AWA Photoinjector";

//----------------------------------------------------------------------------
//Global Parameters

REAL rf_freq             = 1;     //RF frequency. (MHz)
REAL n_particles         = 1E4;      //Number of particles in simulation.
REAL beam_bunch_charge   = 1e-9;  //1e-9;      //Charge of bunch. (C)

// Complete accelerator
lens: RFCAVITY, TYPE=STANDING, FREQ=0, ELEMEDGE=0, L=6.28, VOLT=1e-11, 
FMAPFN="e-lens-fixed.T7";
DRIVE: Line = (lens);

Dist: DISTRIBUTION, TYPE = BINOMIAL,
        MX = 1e6,
        MY = 1e6,
        MZ = 0.5,
        SIGMAX = 1e-3,
        SIGMAY = 1e-3,
        SIGMAZ = 1e-3,
        SIGMAPX = 1e-4,
        SIGMAPY = 1e-4,
        SIGMAPZ = 0.0,
        OFFSETZ = 1e-3;

FS_SC: Fieldsolver, FSTYPE = FFT, 
            MX = 16, MY = 16, MT = 16,
            PARFFTX = False, 
            PARFFTY = False, 
            PARFFTT = True,
            BCFFTX = open, 
            BCFFTY = open, 
            BCFFTT = open,
            BBOXINCR = 4, 
            GREENSF = INTEGRATED;

BEAM1:  BEAM, PARTICLE = ELECTRON, NPART = n_particles, ENERGY=0.001,
        BFREQ = rf_freq, BCURRENT = beam_bunch_charge * rf_freq, CHARGE = -1;

TRACK, LINE = DRIVE, BEAM = BEAM1, MAXSTEPS = 1900000, 
    DT = {3.0e-12}, ZSTOP={6.28};

RUN, METHOD = "PARALLEL-T", BEAM = BEAM1, 
    FIELDSOLVER = FS_SC, DISTRIBUTION = Dist;
ENDTRACK;

Quit;

Attachment: e-lens.T7
Description: e-lens.T7

Attachment: e-lens-fixed.T7
Description: e-lens-fixed.T7