Frequently asked questions for the TOPS Web Page

Q1: I noticed that some of the multigroup opacities were all 1010 . Why did this happen?

A: The TOPS code calculates the plasma cutoff frequency for each temperature-density point. Any group that lies either partly or fully below that frequency has the opacity set to 1010 to indicate that photons at those frequencies cannot propagate in the plasma.

Q2: I want a table of opacities at 21.8 eV. When I enter this number, the Web Page gives me an error message. Why can I not get the 21.8 eV temperature?

A: The TOPS code can only use tabulated temperature points for cross section data. It will not interpolate on temperature. If you choose a temperature that is not on the tabulated grid, the Web Page will compare it to the master list and reject it if it does not agree with one of the table values to within 1 percent. The set of tabulated temperatures is listed under tabulated temperatures.
NOTE: The TOPS code will interpolate in density.

Q3: I entered a temperature of .0005 keV (which is on the allowed temperature list) for carbon and did not get any results back. Why can't I get any data for this temperature?

A: The materials in this data base were calculated over several years and the temperature-density limits were changed during the course of the calculations. Most elements go down to .0005 keV, but the elements from lithium to magnesium only go down to .001 keV. These should be replaced in the next few months and the limitations shown in the tabulated temperatures list will be removed.

Q4: I asked for multigroup opacities for a density of 100 gm/cc for aluminum at a temperature of .001 keV. Every multigroup had the same opacity in it. Why doesn't it vary with photon energy?

A: When you ask for a temperature-density point, TOPS attempts to find cross section data for that point. At low temperatures there is no data available for high densities. Thus the TOPS code uses the cross sections for the highest density available, prints a warning message that this has occurred and uses the gray opacity from those cross sections for all the multigroup and frequency dependent opacities.

Q5: When I specify multigroup opacity, it returns tables containing Rosseland Mean and Planck Mean opacity. But I want to obtain opacity as function of energy (not the averaged opacity). Is there a way I can do this?

A: When you ask for multigroup opacities, you get the Rosseland and Planck mean as well as the multigroup opacities. When you are looking at the the tabular output, the gray opacities appear in the output first. You may need to scroll down in the window to get to the section of the table that contains the multigroup opacities. Of course, you must have checked the button requesting multigroup opacities on the initial input page, as well as set up the group boundary energies. It is also possible to obtain the frequency dependent opacities for a limited number of temperature-density points. The frequency dependent data is tabulated on a grid of either 3000 or 3900 points depending on whether the old or new version of the data is used. The default is to use the new version where available. Because of the large number of points, we limit the requests to only six temperature-density points ie. you could choose two temperature and three density points for a total of six points, or one temperature with six densities etc. In the output file, the frequency dependent data is listed after the gray opacities, or after the multigroup opacities (if requested).

Q6: What is meant by "No. Free" in your tables ?

A: For a single element, the free electron number is the average number of free electrons per ion. It is obtained by multiplying the relative population of each ion stage by the number of free electrons for that stage, zero for the neutral, one for single ionized etc. For a mixture, it is a weighted average using the number fractions of each constituent of the mixture.

Q7: What is your meant by "Av Sq Free" in the output?

A: This is the average of the square of the number of free electrons over the ion stages of an element. It is obtained by summing the product of the relative abundance of each ion stage times the square of the number of free electrons for that ion stage, zero for neutral etc. For a mixture, it is a weigthed average over all constituents of the mixture.

Q8: I can't seem to find opacities for densities lower than 10-12 gm/cc.

A: All of the opacity data is generated assuming Local Thermodynamic Equilibrium (LTE) and this becomes very questionable below 10-6 to 10-7 gm/cc. At lower densities, one should use a nonLTE coronal model. Since the data on this web site assumes LTE, they do not go to such low densities.

Q9: When I display a GIF plot or a data table for the second time, all that I get is the first plot or table over and over again.

A: The Web Page displays a file when showing plots or tables and uses the same file name for each new data set. Many browsers store the file name and data in their cache memeory and if you request a second plot or table, the browser retrieves it from the cache memeory instead of displaying the new data. You must change your browser's cache preference settings from "once a session" to "every time" to force the browser to choose the new data file for each new plot or table. Clicking the Reload button on your browser will also give you the latest plot or table, but you will have to do that every time if you do not reset the brower preference.

Q10: When I plot the Rosseland gray opacities, all of the high density curves seem to run together into one curve. Why is this?

A: The opacity code is unable to calculate the opacities for the low temperature-high density grid points, but needs to have a non-zero value for these grid points. The TOPS code takes the value for the highest calculated density for each temperature and used that value for all of the higher densities. This makes the curves run together.

Q11: I calculated a SESAME table for the same material that I had in the SESAME library that I received from you and the numbers are not quite the same. Why is that?

A: The normal SESAME library is calculated on the CRAY computers, using a slightly different interpolation scheme than on the Sun that runs this Web Page. This can cause small numerical differences. In addition, the boundary region (between calculated points and extrapolated points) is handled quite differently for the two SESAME files. The normal library file is done iteratively (with some points being removed) while the Web Page has to use an automatic fail proof method. Finally the extrapolated points are completely different (see the SESAME Format writeup), but these points should never be used in calculations.

Q12: When I display a postscript plot with Ghostview, I have trouble reading the Legends on the plot or I can not get the landscape mode to display horizontally. What should I do?

A: We have tried Ghostview on different platforms and have found that it operates quite differently on the different platforms. The Macintosh version seems the most limited. All that we can suggest is that you play with the settings and/or preferences until you have the best possible display. The other option is to switch to the GIF format.

Q13: I plan to use some of your opacities in a publication. What is the best reference to cite?

A: You can click on the Opacities methods and references for a list of refernces. The latest reference is

N. H. Magee, Jr., J. Abdallah, Jr., R. E. H. Clark, et al., "Atomic Structure Calculations and New Los Alamos Astrophysical Opacities", Astronomical Society of the Pacific Conference Series (Astrophysical Applications of Powerful New Databases, S. J. Adelman and W. L. Wiese eds.) 78, 51 (1995).

You may also refer to the web page:

TOPS Opacities

Please mail questions or comments to:
LANL T-1 Opacities <>