The OPAL Discussion Forum

[Zhi Li <zhili29882 AT gmail.com>]

Hello OPAL team,

I am a student learning how to use OPAL for a simple RF Cavity simulation. So far I have played around with the  AWA RF Photo Injector example file and made modifications to the input file to suit my simulation needs. Since I don't fully understand how how every line on the input file works, I have some questions. Please be thorough and point out the obvious as much as possible to lead me in the right direction. Thanks in advance!

Questions:

1) If I generate my initial distribution using the NONEQUIL emission model, does the longitudinal momentum of the particles from this override the longitudinal momentum (P0) define in the BEAM parameters? If yes, how do I set this BEAM parameter longitudinal momentum (P0) to 0?

2) Is there a way to have the thermal emittance value saved to the output file (.stat) from the emitted distribution by NONEQUIL? Perhaps I can define a monitor very close to the cathode and capture this value? So far the closest I can set the monitor to the cathode is one micrometer away, is there a way to set it to 0 so its right ontop of the cathode? What is the exact formula that OPAL uses to calculate this thermal emittance? I want to confirm the thermal emittance value captured by a monitor with theoretical calculation by plugging in laser energy, work function, cathode temp, and Fermi energy into an equation. 

3) In the output (.stat) file, I can plot the field seen by the reference particle. What is the exact definition of this reference particle? I don't seem to find a good description of this in the user manual. Is this the first particle emitted from the cathode or does it represent the average of every particle in the bunch?

Best regards,

Zhi

Here is my input file:

OPTION, PSDUMPFREQ = 300;  
OPTION, STATDUMPFREQ = 1;  
OPTION, BOUNDPDESTROYFQ=10;
OPTION, AUTOPHASE=4;      
                           
OPTION, VERSION = 20300;

Title, string="Original AWA Photoinjector input file modified";

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

REAL rf_freq             = 2.998e3;     //RF frequency. (MHz)
REAL n_particles         = 1E3;      //Number of particles in simulation.
REAL beam_bunch_charge   = 1e-3;      //Charge of bunch. (C)

//Initial Momentum Calculation
REAL Edes    = 1e-9; //initial energy in GeV
REAL gamma   = (Edes+EMASS)/EMASS;
REAL beta    = sqrt(1-(1/gamma^2));
REAL P0      = gamma*beta*EMASS;    //inital z momentum

//Printing initial energy and momentum to terminal output.
value , {Edes, P0};

//----------------------------------------------------------------------------
REAL gun_inj_phase = 0;  

GUN:    RFCavity, L = 0.1, VOLT = 110.26, ELEMEDGE = 0.0, TYPE = "STANDING",
        FMAPFN = "DriveGunGPTmap.T7", FREQ = 2998, LAG = (gun_inj_phase*Pi)/180.0,
 APVETO = TRUE;
//----------------------------------------------------------------------------
// DEFINE BEAM LINE

myLine:  Line = (GUN);
//M: MONITOR, ELEMEDGE = 1e-9, OUTFN = 'mon';

// Complete accelerator
DRIVE: Line = (myLine);
//----------------------------------------------------------------------------
Dist:DISTRIBUTION, TYPE = GAUSS,
 SIGMAR = 0.001,
 CUTOFFR = 2.0,
 SIGMAT = 1e-12,
 CUTOFFLONG = 2.0,
 NBIN = 10,
 EMISSIONSTEPS = 100,
 EMISSIONMODEL = NONEQUIL,
 ELASER = 6.48,
 W = 4.31,
 FE = 7.0,
 CATHTEMP = 300,
 EMITTED = TRUE,
 WRITETOFILE = True;
//----------------------------------------------------------------------------
FS_SC: Fieldsolver, FSTYPE = FFT,
            MX = 10, MY = 10, MT = 10,
            PARFFTX = True,
            PARFFTY = True,
            PARFFTT = True,
            BCFFTX = open,
            BCFFTY = open,
            BCFFTT = open,
            BBOXINCR = 1,
            GREENSF = INTEGRATED;
//----------------------------------------------------------------------------
// Electron Beam Definition

BEAM1:  BEAM, PARTICLE = ELECTRON, pc = P0, NPART = n_particles,
        BFREQ = rf_freq,BCURRENT = beam_bunch_charge * rf_freq, CHARGE = -1;

//----------------------------------------------------------------------------
TRACK, LINE = DRIVE, BEAM = BEAM1, MAXSTEPS = 1900000,
    DT = {1.0e-13}, ZSTOP={0.12};

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

Quit;