XGC-S Input Parameters

At the moment XGC-S has a separate input from the main tokamak XGC code, although some input variables are the same. Here we list the most important differences. It is recommended to start from a stellarator example in XGC-Examples when preparing an input file for relevant input variables.

  • XGC-S has an additional namelist &sml_param_stellarator that contains the following input variables:

    • sml_special_s - Simulation mode: 1 = general, 2 = flux-ave (default), 4 = trace.

    • sml_dir_file_s - (8 characters) directory name for equilibrium data (../equilibrium/****/ folder).

    • sml_infile_s - (8 characters) equilibrium files prefix.

    • sml_outfile_s - (6 characters) output files prefix.

    • sml_prf_file_s - (14 characters) profiles filename (../profile/**********/ file).

    • sml_step1_s - Initial time step of simulation.

    • sml_step2_s - Final time step of simulation.

    • sml_delta_s - Time step length in seconds.

    • sml_icon_vol_s - Node volume data (*.vol files in sml_dir_file_s): 0 = generate volume data, 1 = read volume data (default). For option 1 the *.vol files for the node volumes of all planes must already exist in the equilibrium data folder.

    • sml_icon_dlf_s - 0 = full-f, 1 = delta-f (default). Must use 1, full-f is not implemented.

    • sml_icon_bnd_s - Particle boundary condition at last closed flux-surface (not completed), must use 0 at present.

    • sml_icon_poi_s - Finite element Poisson solver: 0 = one dimensional field equation (default), 1 = Poisson solver (turbulence component), 2 = Poisson solver (average component), 3 = Poisson solver (turbulence + average component).

    • sml_icon_iso_s - Switch for mixed isotope plasma, not used at the moment.

    • sml_prep_poi_s - Iterative solver preparation (initial flux). Use 0.

    • sml_prep_poi_e - Iterative solver preparation (last flux). Use 0.

    • sml_icon_col_s - Collision scheme: 0 = no collisions. Collisions not implemented yet.

    • sml_icon_tokamak_s - Switch for equilibrium: 0 = stellarator simulation (default), 1 = tokamak wedge simulation.

    • sml_eqcef_s - Coefficient for equilibrium magnetic field. Normally use 1.0 (default).

    • sml_rdcef_s - Size of applied background radial electric field. Normally use 0.0 (default).

    • sml_diag_freq - Diagnostics time step output frequency.

  • In namelist &sml_param the input variables sml_dt, sml_mstep, sml_restart and sml_restart_write_period are ignored and replaced by the corresponding input in &sml_param_stellarator. If restarting a simulation set sml_step1_s to the next step after sml_step2_s in the previous simulation.

  • In namelist &sml_param the input variables sml_node_file and sml_ele_file are ignored and replaced by the equilibrium input in &sml_param_stellarator.

  • In namelist &sml_param the input variables sml_mode_select_on and sml_mode_select_n are ignored unless sml_icon_tokamak_s = 1 because it is not possible to select a mode in a stellarator simulation.

  • In namelist &sml_param the input variables sml_nphi_total and sml_wedge_n must be consistent with the flag -nv for the number of toroidal cross-sections and the toroidal periodicity from the VMEC file (or torus wedge number for a tokamak) used when generating the equilibrium files with VMEC2XGC2 to ensure that the simulation is correct. Normally sml_wedge_n should be set to the toroidal periodicity and sml_nphi_total should be set to the value of -nv subtracted by 1 and then divided by 2, e.g. if using -nv 9 then set sml_nphi_total = (9 - 1)/2 = 4 when running XGC-S. However, it is also possible to use another combination of multiples of the -nv value and the periodicity, e.g. if using -nv 9 for the mesh and the periodicity is 5 one can also run XGC-S with sml_nphi_total = 4*5 = 20 and sml_wedge_n = 1 instead of using sml_nphi_total = 4 and sml_wedge_n = 5. For a tokamak simulation, sml_icon_tokamak_s = 1, these restrictions do not apply since all cross-sections are identical.

  • In namelist &sml_param the input variables sml_outpsi, sml_bd_ext_delta3, sml_bd_ext_delta4, sml_bd_ext_delta3h and sml_bd_ext_delta4h must be consistent with the flag -truncate used when generating the equilibrium files with VMEC2XGC2. sml_outpsi minus each of sml_bd_ext_delta3, sml_bd_ext_delta4, sml_bd_ext_delta3h or sml_bd_ext_delta4h should be smaller than the value of -truncate to avoid errors in the Poisson solver.

  • In namelist &eq_param the input variables eq_filename, eq_den_file, eq_tempi_file and eq_tempe_file are ignored and replaced by the corresponding input in &sml_param_stellarator.

  • Several namelist in main XGC are not included in XGC-S and many input variables in main XGC are either not included or ignored in XGC-S.

Profiles

The input profiles specified in the file given by sml_prf_file_s has a different format than the main tokamak XGC code. The header line contains the number of equidistant intervals in normalized poloidal flux (label) that the profiles are specified on. This should typically be set to 1000. Then the 1st column is the label index and should run from 0 to 1001. The remaining 4 columns contain ion density in \({\mathrm{m}}^{-3}\), ion density gradient, ion temperature in \({\mathrm{eV}}\) and ion temperature gradient for the flux-surfaces. The gradients are with respect to the normalized poloidal flux \(\psi/\psi_a\). Note that the label index 1000 corresponds to the last closed flux-surface \(\psi/\psi_a = 1.0\), i.e. label 1001 is one radial grid point outside the last flux-surface. Label 0 corresponds to the axis \(\psi/\psi_a = 0.0\).

 1000
    0     5.624773740559e+19     0.000000000000e+00     7.118281580739e+02     0.000000000000e+00
    1     5.624773740559e+19     1.346323821783e+17     7.118281580739e+02     5.111429221637e+00
    2     5.624784215859e+19     7.466412884047e+16     7.118321351095e+02     2.834688018309e+00
    3     5.624788688332e+19     3.953354175467e+16     7.118338331249e+02     1.500927420624e+00
    4     5.624792130482e+19     3.173288427232e+16     7.118351399692e+02     1.204768440686e+00
[...]
 i        n_i                    d(n_i)/d(psi/psi_a)    T_i                    d(T_i)/d(psi/psi_a)
[...]
  999     4.460481422239e+19     3.640960420413e+14     3.549810715080e+02     8.692819217686e-03
 1000     4.460481459376e+19     3.778929072538e+14     3.549810803744e+02     9.022220619954e-03
 1001     4.460481459376e+19     0.000000000000e+00     3.549810803744e+02     0.000000000000e+00

Example of a profiles file for XGC-S.