The input parameters and options for calculating single event upset rates are
described below. When the input form has been completed, pressing the
button will start the calculation and
bring up the "Results" page.
To propagate the fluxes through the spacecraft wall, the CREME software is used. The thickness of the wall is set by the shielding thickness which must to be defined in units of mils, cm or g/cm2.
In a single run, the user can do calculations for as many as 15 devices with different parameters. After defining the number of devices, the user can start to set-up device by device.
First the material of the sensitive volume has to be defined: silicon or gallium-arsenide. For both materials the stopping powers are derived from different sources. For silicon: the creme86 data or SRIM(2008) data, for gallium-arsenide: SRIM(2008) data or GEANT4.9 data. Next the user has the option to define a new device (user defined) or to select a device from a library. In the latter case, the device data (retrieved from the literature) are implemented and cannot be changed. They are given in the report file. For the 'user defined case' the user has to provide:
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
the particle spectrum contain protons. For both mechanisms either model parameters are required or experimental cross section data.
By default the direct ionisation upset rate is calculated using the LET spectra whereby the maximum LET of the stopping ion applies over its entire path length in the sensitive volume (= CREME method). This method may result in calculated energy depositions that exceed the residual energy of the ion and thus overestimates the upset rate. In SPENVIS two alternative algorithms have been implemented: the variable LET method and the slowing and stopping method. The first method accounts for the variation of the LET during passage and the second makes use of the ion energy spectrum instead of the LET spectrum.
The SEU rates (direct ionisation, proton induced and total) are computed either ″per mission segment″ or ″along the orbit″ in units of bit-1, bit-1day-1 or bit-1s-1. The choice is set by the output resolution which is also an input parameter.
The report file spenvis_nuop.html contains the input parameters
and summary tables. The upset rate file spenvis_nuoo.txt
contains, for each orbital point, the direct ionisation and proton induced
nuclear reactions upset rates, as well as the combined upset rates. The corresponding LET and proton fluxes per orbital point are given in the file spenvis_nloo.txt. These files
is only produced when the output resolution was set to full spectra for each orbital point.
The experimental cross section data supplied by the user are stored in the
spenvis_nuof.txt file. Also a file spenvis_nlol.txt with the spacecraft shielded ion energy and LET spectra is generated. In case the user imported a path length distribution, a file spenvis_nuol.txt
with the imported values is created for plotting. The following files come along with the variable LET method for direct ionisation: spenvis_nlof.txt (particle averaged LET vs. energy), spenvis_nloq.txt (particle averaged LET vs. energy values along the orbit).
Plots are available only when the output resolution
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
The current page will be updated with the newly generated plot files.