USER MANUAL
Contents
1. v Tidy up memory and end 192. Pass Parameter Short The pass number zl Column zl Double Position wrt start of electron bunch Intens Column A A2 Double Output intensity Phase Column phi Double Phase of field Ar Column Ar Double Real part of field Ai Column Ai Double Imaginary part of field The optical file is used by feloPlotOptical which plots z1 against intens The time file The time file is a sdds file containing the following data 17 Name Data set type Symbol Type Description Pass Parameter Short The pass number maxintensi Column max Double Maximum ty intensity across output pulse Meanp Column meanp Double Mean electron momenta in bunch Gain Column G Double Single pass gain The time file is used by feloPlotTimeSeries which plots maxintensity meanp and gain against pass The electrons file The electrons file is a sdds file containing the following data Name Data set type Symbol Type Description Pass Parameter Short The pass number Theta Column theta Double Electron phase p Column p Double Electron momenta The electrons file is used by feloPlotPhaseSpace which plots P against theta for each pass 18 The FELO algorithm Start Vv Read input file name and create output file stubs y Read input data read_data Vv Continuation parameter Vn c invalid Vv conti
3. Fortran 90 The code solves universally scaled FEL equations to simulate oscillator FELs operating from the low into high gain regime The code can simulate start up from shot noise different electron pulse current distributions the effects of cavity length detuning and temporal jitter between electron bunches The use of universally scaled equations means that simulations can be performed which are independent of specific undulator and electron beam specifications thus making the program extremely flexible The conversion of physical parameters to and from the universally scaled parameters can be carried out using the Excel spreadsheet FELOparamsCalc that comes as part of the FELO package This may also be used to create an input file for FELO The output data is written to SDDS Self Describing Data Sets compliant files which can subsequently be plotted using SDDS plotting routines Sample plots are shown below FELO has been used to model both the low gain IR FEL and the regenerative amplifier VUV FEL of the 4th Generation Light Source 4GLS proposal see paper FELO6paper pdf that comes with the FELO package FELO predictions for the VUV FEL have been compared with those performed with the parallel implementation of Genesis 1 3 and have been found to be in good agreement Compilation amp quick start The FELO download includes the following files felo4sdds_3 2 f90 compile _felo3_ 2 globalVars f90 randgen f90 tes
4. using feloPlotOptical output intensity is plotted against position 11 li feloPlotTimeSenes This module plots three graphs showing the variation of maxI peak intensity of pulse G single pass gain and meanp mean electron momenta in bunch with pass number the second two plots open upon closing the previous graph window The command to run feloPlotTimeSeries on a file testdata optical is feloPlotTimeSeries testdata amp Sample output from feloPlotTimeSeries is shown in Figure 4 20 irfelAtest3 1 time ine 1 5 KH it 0 D O65 0 0 O 50 100 150 200 pass Time series of max pulse intensity and mean electron momenta irfelAtest3 1 time eh xo irfelAtest3 1 time iis 0 7 LM D Ss ae 1 8 1 6 0 5 2 D 5 1 4 0 4 2 1 2 i i 1 0 0 2 08 0 50 100 150 200 O 50 100 150 200 pass pass Time series of max pulse intensity and mean electron momenta Time series of max pulse intensity and mean electron momenta Figure 4 Plots using feloPlotTimeSeries maximum intensity single pass gain and mean electron momenta in bunch are plotted agaist pass 12 iii feloPlotPhaseSpace The feloPlotPhaseSpace command plots the momentum of the electrons against theta for the number of passes specified by the parameter pulse_num in the input file As with feloPlotOptical the pulse shapes for diff
5. Electron detuning Max Madey gain is for delta_e 2 6056 L_w 3 REAL delta_c Cavity detuning true LOGICAL add_noise Adds electron shot noise if TRUE 80e 12 REAL Q Total charge of electron pulse Only used if add_noise TRUE 10 00166 REAL rho rho parameter Only used if add_noise TRUE 12 outputchoice The maximum random variation of delta_c Figure 2 Example input file Input parameters This section lists the FELO input parameters and details on how to calculate them The Excel spreadsheet FELOparamsCalc can be used to calculate these parameters from the real units of the electron beam undulator parameters etc shape Character The shape of the electron pulse current one of rectangular triangular parabolic or gaussian should be chosen sigma_e Real The scaled RMS width of the electron pulse current this is only used for Gaussian pulses and is given by AMP yO oo A y where oz m is the RMS bunch length 4 m is the radiation wavelength and pepis the effective Pierce parameter see below pulse_num Integer The number of electron pulses to enter cavity the number of cavity passes Le Real The scaled electron pulse length For all pulse shapes except Gaussian L_e is the full width For Gaussian pulse shape a value of L_e 6xo contains 99 7 of the electron beam current L w Real The scaled interaction length of the undulator L_w 4aN Py whe
6. am energy spread and emittance F is the filling factor and pis related to g by the equation xg j 4nzN where 23 Z 8 amp 7 m An explicit expression for go applicable for a planar undulator and more details on calculating the effective Pierce parameter are included in the paper FELO6paper pdf contained in the FELO package outputchoice Either 1 2 or 3 corresponding to full medium or short output e Full time optical and electrons files e Medium time and optical files e Short time file only The optical file is used by feloPlotOptical which plots output intensity against position for each pass The time file is used by feloPlotTimeSeries which plots maximum intensity mean electron momenta and single pass gain against pass The electrons file is used by feloPlotPhaseSpace which plots electron momenta against electron phase for each pass see section on SDDS postprocessors jitter Real The jitter on the cavity length detuning delta_c in universally scaled units of L_w of above General tips Some points about input files e Input files for the FELO program should have a in suffix e g testdata in e There is a limit of 26 characters for the length of file names which if exceeded causes errors when using the plotting programs Running FELO Once the input file is prepared the FELO program can be used to perform simulations To start a new simulation on input file testdata in the foll
7. erent passes are shown on different plots and can be scrolled between by pressing n p and m The command to run feloPlotPhaseSpace on a file testdata optical is feloPlotPhaseSpace testdata amp Sample output from feloPlotPhaseSpace is shown in Figure 5 irfelAtest3 1 electrons 0 2 4 6 8 1012 theta Electron Phase Space Figure 5 Plot using feloPlotPhaseSpace electron momenta is plotted against electron phase Phase space plots for each slice are overlaid on top of each other 13 Conversion of output into standard units The conversion of the FELO output into standard units can be done using the FELOparamscale spreadsheet Figure 6 shows output from FELO converted into real units VUVFELde3v2 optica FELd ptical 300 0 8 200 lee i 0 6L an a IAIT 2 2 ST T 100 T 50 OF S34 Ola 20253053 0 014 02 03 04 05 06 z1 t ps Optical Intensity Figure 6 FELO output plotted with feloPlotOptical left and converted into real units right e Zl into metres The value z1 is the position with respect to the start of electron bunch a distance in universally scaled units This is converted into distance in metres z in the following relation using z _ xzl AT Py where pep is the effective Pierce parameter and 4 is the radiation waveleng
8. ling again This can be done using the command chmod x mod Using FELO Using the FELO program follows the steps shown in Figure 1 The following sections of this manual give detailed information on each of these stages Create Run Plot Convert to input file FELO data standard units Figure 1 Flow diagram showing the process of performing simulations using FELO Input Files An example of a FELO input file is shown in Figure 2 The following section describes how to calculate input file parameters this can also be done using the Excel spreadsheet provided FELOparamsCalc ALUE TYPE Name Description gaussian CHARACTER shape The shape of the electron pulse current rectangular triangular parabolic or gaussian 15 34649 REAL sigma_e The width of the pulse electron pulse current Only used for gaussian 130 INTEGER pulse_num Number of electron pulses to enter cavity the of oscillator passes 32 079 REAL Le Scaled electron pulse length in z_1_bar 3 95992 REAL Lw Scaled interaction distance in z_bar 0 1 REAL reflect Reflectivity of output cavity mirror 50 was 50 INTEGER e_per_node Number of electrons per node A node is a ponderomotive potential 100 INTEGER nodes_e Number of nodes in electron pulse for non overlapping must have nodes_e lt L_e L_w N_w 7 12129e 15 REAL a_0 Scaled initial field amplitude 0 657994 REAL delta e
9. nuation 2 continuation 1 end Write input data to SDDS file Vv Initialise variables not changed during integration Vv Assign the current weighting to electrons Vv Initialise electron and field variables Vv Continuation parameter continuation 2 I continuation 1 Set real part of scaled field to a_0 and imaginary part to 0 Read in pass number and optical pulse data Ll CALL NEWPASS Gets random number using computer clock time Calculates the electron shot noise if any Get new electron variables Reflect field from output mirror or initialise the field Vv Integrate equations Vv z 0 Vv Integrate through one pass of the cavity Runge Kutta routine a z zthz CALL output CALL write_optical_data gt optical file y 5 CALL write_electron_data gt electrons file CALL NEWPASS y CALL write_shortdata gt time file Get a random seed scale according to assigned jitter CALL write_logfile gt log file value and add to the cavity length detuning y CALL DETUNE modify radiation due to the effects of gt radiation damping i gt start_pulse pulse_num 1 CALL DUMP save pass number and pulse profile for further run
10. owing command should be entered at the terminal window FELO3_2 testdata in n To continue an old simulation n should be replaced with c FELO3_2 testdata in c see known bugs section problem with using c The program will output a header containing the input information and then as each cavity pass is completed the value of the single pass gain is output along with the date and the time to the terminal window For the example testdata in file the FELO program creates the following output files e testdata optical e testdata time e testdata electrons e testdata log e testdata par e testdata dump The content of these files is detailed in the appendix 10 The SDDS postprocessors There are three SDDS postprocessors i feloPlotOptical The feloPlotOptical program plots the scaled radiation power A against scaled distance for the number of passes specified by the parameter pulse num in the input file The output for the different number of passes are shown on separate plots and can be scrolled between by pressing n on the keyboard for next page or p for previous Pressing m scrolls through all pages The command to run feloPlotOptical on a file testdata optical is feloPlotOptical testdata amp Sample output from feloPlotOptical is shown in Figure 3 irfelAtest3 1 optical he 0 0 O 5 10 igs 20 z Optical Intensity Figure 3 Plot
11. ptical testdata amp Plots three graphs showing the variation of maxT intensity G single pass gain and meanp mean electron momenta in bunch with pass number feloPlotTimeSeries testdata amp Plots the momentum of the electrons against phase for each pass feloPlotPhaseSpace testdata amp Known bugs Using the c command to continue an old run produces the following errors in the time file e the number of passes is not updated e the maxintensity value for the first pass of the continuation is given as HHHHHHHHHH rather than a number These need to be corrected manually by opening the time file and amending the data before using feloPlotTimeSeries Note on length of file names file name lengths must be less than 26 characters 16 Appendix Output Files This section describes the data contained in the three sdds files produced by the FELO code The output depends on the value of the parameter outputchoice specified in the input file A value of 1 corresponds to full output which consists of three files with the in suffix of the input file name replaced by optical time electrons A value of 2 gives the optical and time files but not the electrons A value of 3 gives the time file only The optical file The optical file is a sdds file containing the following data Name Data set type Symbol Type Description
12. re N is the number of undulator periods reflect Real The power reflectivity of the output cavity mirror as a decimal The upstream mirror is assumed 100 reflective e per_node Integer The number of electrons per node A node is one ponderomotive potential nodes _e Integer The number of nodes in the electron pulse for non overlapping ponderomotive potentials L nodes e lt fN T Lw a 0 Real The initial scaled field amplitude If electron shot noise is used see add_noise below a_0 should be set to a very small value When electron shot noise is disabled the following expression for a_0 can be used I peak cde where N delta _e Real The electron detuning Max Madey gain is for delta_e 2 6056 L_w delta_c Real The cavity length detuning in units of the scaled interaction length see L_w above A positive detuning corresponds to a shortening of the cavity length add_noise Logical Adds electron shot noise if TRUE no shot noise if FALSE Q Real Total charge of electron pulse in Coulombs only used if add_noise TRUE rho Real Effective Pierce parameter only used if add_noise TRUE The effects of energy spread beam emittance and transverse filling factor on the FEL interaction are accounted for by using an effective Pierce parameter Pop oY P when applying the universal scaling where F is the gain attenuation factor accounting for be
13. rn USER MANUAL B W J McNeil G R M Robb SUPA Department of Physics University of Strathclyde Glasgow UK N R Thompson D J Dunning ASTeC CCLRC Daresbury Laboratory UK Contents INTRODUCTION 3 ABOUT FELO 4 COMPILATION amp QUICK START 5 USING FELO 6 INPUT FILES 6 Example Input File 6 Input Parameters General Tips 10 RUNNING FELO 10 THE SDDS POSTPROCESSORS 11 i feloPlotOptical 11 ii feloPlotTimeSeries 12 iii feloPlotPhaseSpace 13 CONVERSION OF OUTPUT INTO STANDARD UNITS 14 SUMMARY OF UNIX COMMANDS FOR FELO 16 KNOWN BUGS 16 APPENDIX 17 Output files 17 The FELO Algorithm 19 Introduction This manual gives details of the one dimensional free electron laser oscillator simulation code FELO It covers code compilation preparation of input files performing simulations and plotting of output data The FELO code is still developing and it is the aim of the authors is to keep this manual up to date as the code is developed further The current and first publicly available version is 3 2 If there is a requirement to modify or extend the code in any way please notify any of its authors Brian McNeil b w j mcneil strath ac uk Neil Thompson n r thompson dl ac uk David Dunning d j dunning dl ac uk Gordon Robb g r m robb strath ac uk 12 September 2006 About FELO FELO Free Electron Laser Oscillator is a one dimensional SDDS compliant time dependent FEL oscillator code that has been developed in
14. tdata in randnum f90 sddsinout4felo f90 feloPlotOptical sddsWriter f90 feloPlotPhaseSpace time Writer f90 feloPlotTimeSeries Open a terminal in linux or cygwin in which the GNU g95 complier has been installed Change to the installation directory Enter the command compile_felo3_2 and FELO should compile using the G95 compiler e The file felo4dsdds_3 2 f90 is the main body of the program e globalVars f90 randgen f90 randnum f90 sddsinout4felo f90 sddsWriter f90 and timeWriter f90 are additional modules e testdata in is an example input file e feloPlotOptical feloPlotPhaseSpace and feloPlotTimeSeries are the Tcl scripted SDDS postprocessors The executable FELO exe should be present in the compilation directory The code may be run using the command FELO3_2 testdata in n The output can be plotted assuming Tcl which may be installed as part of cygwin and the SDDS ToolKit is installed using the commands feloPlotOptical testdata amp feloPlotTimeSeries testdata amp and feloPlotPhaseSpace testdata amp The SDDS site also supplies IDL and MATLAB interfaces 1 Note There may be error messages during compilation referring to missing mod files these are created during the compilation process and are not always automatically executable It may be necessary to update the permissions in order to make these files executable before compi
15. th e maxI A 2 into MW The value maxI is equal to the maximum power across the output pulse from feloPlotTimeSeries and A 2 is the scaled output power from feloPlotOptical These are related to the power in watts by the following expression P pdf EI 14 where E is the beam energy in eV Z is the Peak Current in amps a is the outcoupling and L is the cavity total loss P is the output power in watts 2 The value of the optimum outcoupling can be estimated from either the following expression Dattoli et al applicable up to G 100 j osd e 0 28 1 G om 0 86 0 56 1 G gain and optimum outcoupling as fractions Alternatively the following expression based on a numerical fit to simulation data can be used applicable up to G 500 oy 2X10 7G 2 9x10 G 0 2G 0 024 gain and optimum outcoupling in The optimum total cavity loss is then given by the optimum outcoupling plus the cavity round trip passive loss 15 Summary of UNIX commands for FELO The table below shows the main commands to be entered in a terminal window for using the FELO program for an input file testdata in Command Action compile felo3 2 Compiles using the G95 compiler FELO3_2 testdata in n Starts new run FELO3_2 testdata in c Continues old run Plots the intensity of the output pulse against distance along the pulse for each pass feloPlotO
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