The OPAL Discussion Forum

[Simon Friederich <sifriede AT uni-mainz.de>]

Dear OPAL-Team,

I wanted to use a collimator in my beamline. Unfortunately it does not affect the beam in any way.

Please have a look at my small "collimator.in" file:
The beamline consists of a cathode, monitor, collimator, monitor. As the collimator does not work (yet), I've placed a DRIFT element with  a tiny aperture in the beam line, which does work as a collimator

(Picture shows two monitors: left: the starting flattop beam distribution, right: the beam profile collimated by the tiny-aperture-drift space

)

But in the end I need a rectangle-shaped collimator which I wanted to achieve using a FLEXIBLECOLLIMATOR + DESCRIPTION = "intersection(rectangle(0.03,0.03), translate(rectangle(0.015, 0.015), 0, -0.015)".

Do I have to "activate" the collimator mechanism somehow in opal-t?

Best regards and thanks in advance
Simon

-- 
-----------------------------------
Dr. Simon Friederich
Helmholtz-Institut Mainz
Kollaboration B/ACID
Johannes Gutenberg-Universität Mainz
Staudingerweg 18
55128 Mainz, Deutschland

Tel.: +49 (0)6131 39-23160
E-Mail: sifriede AT uni-mainz.de
----------------------------------------

TITLE, STRING="Chopper cavity test";

OPTION,
        VERSION = 23000,
        //SEED = 123456789, // fix seed for particle generation and 
comparison reason
        ECHO = false,
        INFO = false,
        STATDUMPFREQ = 1, // after how many time steps we dump statistical 
data
        ENABLEHDF5 = true,
        PSDUMPFREQ = 100, // Affects the stdout information **BUNCH**
        EBDUMP = false,
        AUTOPHASE = 6; // how accurate the search for the phase at which the 
maximal energy is gained (default=6, off=-1)

//----------------------------------------------------------------------------
// Beam parameter
REAL freq_Hz = 1.3e9;
//REAL Qbunch = 0.77e-12; // 1mA
REAL Qbunch = 0.77e-15; //1 uA
REAL current = Qbunch*freq_Hz;
REAL lambda_m = 2.998e8/freq_Hz;
REAL gamma = 611/511;
REAL beta = sqrt(1-1/gamma^2);

// Simulation parameter
REAL nelectrons = 10000; //[1e4]
REAL dt_s = 5e-12; //[10e-12] time step in s
REAL zstop = 0.4; // in m


//----------------------------------------------------------------------------
// Distribution
distr_gauss_injected:
        DISTRIBUTION,
        TYPE = GAUSS,
        SIGMAR = 0.5e-3, CUTOFFR = 3,
        SIGMAZ = 0.0215, CUTOFFLONG = 3,
        WRITETOFILE = True,
        EMITTED=false;
        //DEBUG SIGMAZ = 0.015960;
        // [SIGMAZ]=m;

distr_flattop_injected:
        DISTRIBUTION,
        TYPE = FLATTOP,
        SIGMAR = 10e-3, 
        SIGMAZ = 0.1,
        EMITTED=false;

//----------------------------------------------------------------------------
// Fieldsolver
fieldsolver_default:
        FIELDSOLVER,
        FSTYPE = FFT, // Specify type of field solver ("none" does not 
respect space charge)
        MX = 20, // Number of grid points in x specifying rectangluar grid
        MY = 20,
        MT = 20,
        PARFFTX = true, // dimension x is distributed among the processors
        PARFFTY = true,
        PARFFTT = false, // changed that!
        BCFFTX = open, // Boundary condition in x,y options: [open]
        BCFFTY = open,
        BCFFTT = open, // Boundary condition in z options: [open, periodic]
        BBOXINCR = 10, // Enlargement of the bounding box in %
        GREENSF = INTEGRATED;

//----------------------------------------------------------------------------
// Source
cathode: SOURCE, ELEMEDGE = 0.0; // not yet known if really necessary

//----------------------------------------------------------------------------
// Collimator
REAL wcol = 0.03;
REAL lcol = wcol;

collimator: FLEXIBLECOLLIMATOR,
        Z = 0.2,
        L = 10e-3,
        // DESCRIPTION = "rectangle(0.1,0.1)",
        DESCRIPTION = "ellipse(0.1,0.1)",
        OUTFN ="col_out.h5";

collimator2: RCOLLIMATOR,
        Z = 0.2,
        L = 10e-3,
        XSIZE=1, YSIZE=1, // Memory access error occurs if this line is 
commented out
        APERTURE="circle(0.01)";

driftcolli: DRIFT, APERTURE = "circle(0.005)", ELEMEDGE = 0.3, L = 1e-3;

//----------------------------------------------------------------------------
//Drifts
beampipe: DRIFT, APERTURE = "circle(0.04)", ELEMEDGE = 0, L = zstop;
beamdump: DRIFT, APERTURE = "circle(0.0001)", ELEMEDGE = zstop, L = 1e-3;

//----------------------------------------------------------------------------
// Monitors
mon0: MONITOR, ELEMEDGE = 0.10, OUTFN="screen_0100";
mon1: MONITOR, ELEMEDGE = 0.40, OUTFN="screen_0300";
mon2: MONITOR, ELEMEDGE = 0.54, OUTFN="screen_0540";
mon3: MONITOR, ELEMEDGE = 0.70, OUTFN="screen_0700";
mon4: MONITOR, ELEMEDGE = 1.00, OUTFN="screen_1000";
mon5: MONITOR, ELEMEDGE = 1.20, OUTFN="screen_1200";
tmp0: MONITOR, ELEMEDGE = 0.70, OUTFN="temp_distr_0700",  TYPE = TEMPORAL;

monline: LINE=(mon0, mon1);
// monline: LINE=(mon0, mon1, mon2, mon3, mon4, mon5, tmp0);

//----------------------------------------------------------------------------
// Beamline
mybeamline: LINE = (cathode, collimator2, monline, driftcolli);

//----------------------------------------------------------------------------
// Beam
mybeam: BEAM,
        PARTICLE = ELECTRON,
        ENERGY = EMASS+1e-4, // in MeV // But for gun no starting energy 
needed
        // ENERGY = EMASS+1e-9, // in GeV
        BCURRENT = current, // in A
        NPART = nelectrons,
        BFREQ = freq_Hz*1e-6; // [BFREQ] = MHz

//----------------------------------------------------------------------------
// Simulation
TRACK,
        LINE = mybeamline,
        BEAM = mybeam,
        MAXSTEPS = 10000,
        DT = dt_s, // in s
        ZSTOP = zstop; // in m

RUN,
        METHOD = "OPAL-T",
        BEAM = mybeam,
        FIELDSOLVER=fieldsolver_default,
        // DISTRIBUTION=distr_gauss_injected;
        DISTRIBUTION=distr_flattop_injected;

ENDTRACK;

// SYSTEM, "python3 python_xy_multimon_enhanced.py $(ls screen_*.h5)";

STOP;