Help file for the TOPS code

Your first choice as a user is the type of data file to use. There are two types of data files: ATOMIC and LEDCOP. The ATOMIC files are the latest data files produced by the LANL opacity team (groups T-1 and XCP-5) and are the preferred files.

See file of currently available materials for the current list of available materials. The material ID numbers are prefixed by the letter n. The LEDCOP files are older cross section files and are included for the sake of continuity.

The default is to use the most recent available data file for each element.

As a user you may choose to mix an arbitrary number of elements. You have the option of specifying the mixture by number fraction or by mass. You may also choose to specify particular isotopic weights in the mixture.

The default is to specify mixtures by number fraction and use the naturally occurring isotopic weights.

You have several options for temperatures. You may select individual temperature, choose a subset of the tabulated temperatures, or thin the tabulated temperatures. In any case, the selected set of temperatures must be elements of the default temperature grid.

The default is to use temperatures in the range of 0.1 to 10 keV.

In a similar manner you can select the density grid. In contrast to the temperature grid, there is no default density grid. You are free to select specific densities, or choose a grid with either logarithmic or linear spacing.

One should exercise some restraint in choosing the total number of temperature and density points, especially for mixtures containing a large number of elements. The run times can become quite long. The Web Page will give you an time estimate on the Output Selection page after you submit your calculation from the first input page. If the time estimate is too long, the Web Page will refuse the calculation.

One point to be noted is that the range of densities for which cross sections are tabulated varies with temperature. At low temperatures there is a relatively low upper bound on density. This causes the TOPS code to attempt to find opacities for which cross section data do not exist. If this happens, the TOPS code prints a warning message on both the columnar table output and on all graphs except the 3-D graphs. It then uses the cross sections for the highest density point for that temperature to calculate the gray opacities. If multigroup opacities are requested, that gray opacity is put into each multigroup spot so that there is no variation of opacity with photon energy. This should point out that the displayed multigroup opacity does not represent a true multigroup calculation for this point. The frequency dependent data is handled the same way as the multigroups.

If you wish to have multigroup opacities, you may select photon group boundaries in keV in a manner similar to the selection of the density grid. The default is to use a logarithmic spacing of 33 boundaries (32 groups) with energies between .001 and 300. keV.

Just as there is a pratical limit to the product of number of temperatures times number of densities, there is a limit on the product of number of temperatures times number of densities times number of group boundaries. Currently this product is limited to 50000. Thus if you choose the default temperature grid with 50 temperatures and a density grid with 20 densities, you can still have 50 photon groups.

If you choose to look at frequency dependent opacities, the TOPS code will automatically output all of the available data for each temperature- density point. At present, this is 3000 or 3900 frequency points for each case. You may restrict the frequency range on the various graphics pages if you do not want to download the entire table.

The TOPS code calculates the plasma cutoff frequency, the frequency below which photons may not propagate in a plasma. Any group which lies partly or fully below this frequency has the opacity in that group set to 1010. Normally this cutoff frequency is very low relative to the temperature and should not make any difference in a radiation transport calculation.

The default mode when you press the submit button is to calculate gray Rosseland and Planck opacities along with the average number of free electrons. You also have the option of requesting multigroup and/or frequency dependent opacities. If you choose the frequency dependent option, you are limited to 6 temperature-density points per calculation. Resulting tables can be saved to your local machine with the FILE button on your web browser.

The normal columnar TOPS tables first list any warning messages. Then the temperature, density and (if requested) multigroup photon energy grids. boundaries. After this, the gray Rosseland and Planck opacities are shown. If you requested multigroup opacities, these are listed next. Finally, the frequency dependent opacities are listed if this calculation was requested.

Special note to SESAME users. This Web Page is now setup to output the special SESAME format ASCII files for opacities. Users must have already obtained the SESAME codes from T-1 at LANL before they can use these tables. See the SESAME writeup for more details about the tables produced by this Web Page.

Please mail questions or comments to:
LANL T-1 Opacities <opacity@lanl.gov>