Table of Contents ECSS Model Page
Background Information Radiation sources and effects
SEU rates

Overview

Single event upset rates are calculated with models from the CREME model suite. Upset rates are derived from ion energy and LET spectra which have to be generated before running the upset rate model.

The input parameters and options for the trapped radiation models are described below. When the input form has been completed, pressing the button will start the calculation and bring up the "Results" page.

The button calls up the model selection page for consecutive runs of multiple models. This feature is available for advanced users only.

Warning: using these buttons deletes all existing output from the upset rate model and from any model that uses this output, in order to ensure consistency in the outputs.

Input parameters

First the shape of the sensitive volume has to be defined. In case of a rectangular parallellopiped, the dimensions (X, Y, Z) have to be entered in µm. For all other shapes, the user has to provide the topsurface, the total surface and volume of the cell and a path length probability density distribution together with the maximum path length inside the volume. The input path length distribution should be normalised and the input density values have to be in units of cm2/g and for an equidistant grid. The first (last) value should hold for zero (maximum) path length.
The user can also select a device from a list of predefined devices of which the details are given in the report file. The advanced user can set up a number of devices (max. 15) so that in a single run the upset rate is calculated in each device for a given LET curve.

Two mechanisms can create SEUs: direct ionisation by ions transported through the spacecraft skin, or ionisation by secondary particles produced by proton nuclear interactions. The parameters for each mechanism have to be supplied if the ion energy and LET spectra contain protons. For both mechanisms, model parameters can be entered, or, alternatively, experimental cross section data can be used.

By default the model for direct ionization assumes that the maximum LET of the stopping ion applies over its entire path length in the sensitive volume which may result in calculated energy depositions that exceed the residual energy of the ion. An improved algorithm, that accounts for the variation of the LET inside the volume, has been implemented but is only available for the advanced user.

Direct ionisation effects

The cross sections for direct ionisation can be specified by a table of cross section vs. effective LET values or by a four parameter Weibull function. If no cross sections are available, the critical charge of the device has to be specified.

Proton nuclear interaction induced effects

The upset rates resulting from nuclear reactions caused by protons use an operational SEU cross section function. If cross section vs. energy values are available, the Bendel or the Weibull function is fitted to the experimental data. Alternatively, the parameters for the Bendel or the Weibull function can be entered directly by the user. If neither of them are available, heavy ion cross section data can be used.

Results

The upset rate model produces the files listed in the table below. A description of the file formats can be brought up by clicking on their description in the table.

The report file spenvis_uop.html contains the input parameters and summary tables. The upset rate file spenvis_uoo.txt contains, for each orbital point, the direct ionisation and proton induced nuclear reactions upset rates, as well as the combined upset rates. This file is only produced when the output resolution for the ion energy and LET spectra was set to full spectra for each orbital point. The experimental cross section data supplied by the user are stored in the spenvis_uof.txt file.

Output files generated by the upset rate model
File name Description
spenvis_uop.html Report file
spenvis_uoo.txt Upset rates for each orbital point
spenvis_uof.txt Experimental cross section data and Bendel or Weibull fit
spenvis_uol.txt Imported path lentgh probability distribution

Plots are available only when the output resolution for the ion energy and LET spectra was set to full spectra for each orbital point, or when experimental cross section data or path length distribtions are supplied by the user.

To generate plots, select the plot type(s), options and graphics format, and click the or button. The current page will be updated with the newly generated plot files.

The button calls up the output page for consecutive runs of multiple models. This button only appears when the upset rate model has been included in the combined model run selection. This feature is available for advanced users only.

Last update: Mon, 12 Mar 2018