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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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: