Particle Beam Setup

Energy can be deposited into the hydro grid by an incident ion beam or electron beam. The particle beam kinetic energy and power can be specified to vary with time, and also by various kinetic energy (KE) distributions.

To specify the particle beam parameters:

• Select the Electrons or Ions radio button.
• Select the incident boundary for the particle beam.
• For ion beam only, specify the element by clicking on Choose Element... and selecting an element from the periodic table widget.
• Specify the kinetic energy (KE) distribution. The distribution option (e.g. Mono-energetic) appears in the first combo-box. For each distribution option (except Tabulated), the distribution is defined by one or more parameters. The parameter being specified appears in the second combo-box. Each parameter can be either time-independent or time-dependent.

  Normalization: the distributions only define the shape. When running the simulation, Helios will normalize the distributions such that the integral of the distribution, between the Binning Min. and Max. Energy, equals the Power at that time, which is defined in the Particle Beam Power section of the page. Note that the times do not need to match. Linear interpolation will be done in the case where time values do not match.

  Additionally, if there are hydro times which are before the lowest input time, the value at the lowest input time will be used. Similar treatment will be done for hydro times beyond the highest input time.

  Input options:

  • Mono-energetic:

    All particles have the same KE, thus "Energy" is the only entry in the combo-box.

  • Tabulated:
    This option uses a multi-column table for input for KE distributions. The first cell should not be edited--it is the title for the first column (energies). The remaining entries of the first row are time values (s). If your KE distribution is constant in time, you can leave this as having just one time column. Each remaining cell is then the dN/dE value for that energy and time. If the distribution is time-dependent, add an additional column (Edit > Add Column), and put its time value in the first cell of the column.

    Here is an example of a table of distributions for two times:

    

    The Table File option can be used by browsing for a text file with the following format. This would enter the same values as the table above:

    [table format=1]: Tabulated Particle beam KE:
    # table rows = 4
    # table cols = 3
    Energy [MeV]
    1.00000e-02 1.00000e-01 1.00000e+00 1.00000e+01
    1e-9
    1.00000e+10 1.50000e+10 2.30000e+10 3.60000e+10
    2e-9
    3.00000e+10 3.90000e+10 5.10000e+10 7.70000e+10

  • Maxwellian:

    The distribution will be a Maxwell-Boltzmann given by temperature "T" in MeV, i.e. the mean KE will also be "T" in MeV. Thus "T" is the only entry in the combo-box.

  • Power Law:

    The distribution will be E^-k where E is the KE, and k is dimensionless. Thus "k" is the only entry in the combo-box.

  • Gaussian:

    The distribution will be Gaussian with central KE given by "E0" and standard deviation"sigma". The combo-box thus has an entry for both "E0" and "sigma".

  Binning:

  The min. and max. energies define the range of the distribution, and should thus likely be chosen to contain the significant part of the distribution . E.g., E0-5*sigma to E0+5*sigma for a Gaussian, or 0.1*T to 10*T for a Maxwellian. For Tabular input, the min.-max. should generally match the table range, unless only part of the table is desired. Outside this binning range, the beam power will be zero.

  As noted above, the binning min. and max. energies also define the integration region for normalizing the energy distribution to the particle beam power.

  The number of particles created per time step will be the number of bins times the number of particles per bin. It is recommended to use 25 - 100 total particles. The number of particles created with energy distributions will be a factor of n_bins*np_per_bin more than in the mono-energetic beam.

• Specify the power by either:
  • Selecting Constant and entering a value or
  • Selecting the Table method, clicking on Setup and entering the values of time and power for the beam. A multiplier for the power can also be entered.

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