Application
Report
SLVK046 – May 2020
Heavy Ion Orbital Environment Single-Event
Effects Estimations
ABSTRACT
This document discusses the methodology used to calculate on-orbit Single Event Effects (SEE) event
rates.
Contents
1
2
Introduction
...................................................................................................................
1
References
...................................................................................................................
3
List of Figures
1
2
Integral Particle Flux Versus LET
EFF
for a LEO-ISS (Blue Curve) and a GEO (Red Curve) Environment as
Calculated by CREME96 Assuming Worst-week and 100 mils (2.54 mm) of Aluminum Shielding
..............
2
Device Cross Section Versus LET
EFF
Showing How the Weibull Fit (Green) is “Simplified” With the Use a
Square Approximation (Red Dashed Line)
...............................................................................
3
1
Introduction
To calculate SEE on-orbit event rates, both the device SEE cross-section and the flux of particles
encountered in a particular orbit are required. Device SEE cross-sections are usually determined
experimentally while flux of the particles in orbit is calculated using various software algorithms based on
empirical data. For the purpose of generating representative event rates, a Low-Earth Orbit (LEO) and a
Geostationary-Earth Orbit (GEO) were calculated using Cosmic Ray Effects on Micro-Electronics 96
(CREME96). CREME96 code is a suite of programs that enable estimation of the radiation environment in
near-Earth orbits
[ , ]
. CREME96 is one of several tools available in the aerospace industry to provide
accurate space environment calculations. Over the years since its introduction, the CREME models have
been compared with on-orbit data and demonstrated their accuracy. In particular, CREME96 incorporates
realistic “worst-case” solar particle event models where fluxes can increase by several orders-of-
magnitude over short periods of time.
1
2
For the purposes of generating conservative event rates, the worst-week model (based on the biggest
solar event lasting a week in the last 45 years) was selected. This event has been equated to a 99%-
confidence level worst-case event
[ , ]
. The integrated flux includes protons to heavy ions from solar and
galactic sources. A minimal shielding configuration is assumed at 100 mils (2.54 mm) of aluminum. Two
orbital environments were estimated: that of the International Space Station (ISS), which is in LEO and the
GEO environment.
Figure 1
shows the integrated flux (from high LET to low) for these two environments.
3
4
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Introduction
1
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LEO (ISS)
GEO
0.1
Integrated Flux (/cm
2
-day)
0.01
0.001
0.0001
1E-5
1E-6
2E-7
20
30
40
50
60
LET
EFF
(MeV-cm
2
/mg)
70
80
90
100
Flux
Note that the y-axis represents flux integrated from higher LET to lower LET. The value of integral flux at any specific
LET value is actually the integral of all ion events at that specific LET value to all higher LETs.
Figure 1. Integral Particle Flux Versus LET
EFF
for a LEO-ISS (Blue Curve) and a GEO (Red Curve)
Environment as Calculated by CREME96 Assuming Worst-week and 100 mils (2.54 mm) of Aluminum
Shielding
Figure 1
shows the Integral Particle Flux versus LET
EFF
for an LEO-ISS (blue curve) and a GEO (red
curve) environment as calculated by CREME96 assuming worst-week and 100 mils (2.54 mm) of
aluminum shielding. Note that the y-axis represents flux integrated from higher LET to lower LET. The
value of integral flux at any specific LET value is actually the integral of all ion events at that specific LET
value to all higher LETs.
Using this data, you can extract integral particle fluxes for any arbitrary LET of interest. To simplify the
calculation of event rates, assume that all cross-section curves are square, meaning that below the onset
LET, the cross-section is identically zero while above the onset LET, the cross-section is uniformly equal
to the saturation cross-section.
Figure 2
illustrates the approximation with the green curve being the actual
Weibull fit to the data with the “square” approximation shown as the red-dashed line. This allows you to
calculate event rates with a single multiplication, the event rate becoming simply the product of the integral
flux at the onset LET, and the saturation cross-section. Obviously, this leads to an over-estimation of the
event rate since the area under the square approximation is larger than the actual cross-section curve, but
for the purposes of calculating upper-bound event rate estimates, this modification avoids the need to do
the integral over the flux and cross-section curves.
2
Heavy Ion Orbital Environment Single-Event Effects Estimations
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1E-5
References
Device Cross-Section (cm
2
)
1E-6
1E-7
1E-8
40
50
60
70
LET
EFF
(MeV-cm
2
/mg)
80
90
100
Exam
Figure 2. Device Cross Section Versus LET
EFF
Showing How the Weibull Fit (Green) is “Simplified” With
the Use a Square Approximation (Red Dashed Line)
Figure 2
shows a device cross section versus LET
EFF
, showing how the Weibull fit (green) is “simplified”
with the use a square approximation (red dashed line).
To demonstrate how the event rates are calculated, assume that you wish to calculate an event rate for a
GEO orbit for the device whose cross-section is shown in
Figure 2.
Using the red curve in
Figure 1
and
the onset LET value obtained from
Figure 2
(approximately 65 MeV-cm2/mg), you find the GEO integral
flux to be approximately 3.24 × 10
–4
ions/cm
2
-day. The event rate is the product of the integral flux and the
saturation cross-section in
Figure 2
(approximately 5.3 x 10
-6
cm
2
):
)'1 'RAJP 4=PA
=
l
3.24 × 10
F4
EKJO
ARAJPO
p
×
:
5.3 × 10
F6
?I
2
;
= 1.71 × 10
F9
?I
2
×
@=U
@=U
ARAJPO
DN
(1)
(2)
(3)
)'1 'RAJP 4=PA
= 0.71 × 10
F10
= 0.071
(+6
/6$(
= 1,607,820
;A=NO
2
References
1.
https://creme.isde.vanderbilt.edu/CREME-MC
2. A. J. Tylka, and others, "CREME96: A Revision of the Cosmic Ray Effects on Micro-Electronics Code",
IEEE Trans. Nucl. Sci., 44(6), 1997, pp. 2150-2160.
3. A. J. Tylka, W. F. Dietrich, and P. R. Boberg, “Probability distributions of high-energy solar-heavy-ion
fluxes from IMP-8: 1973-1996”, IEEE Trans. on Nucl. Sci., 44(6), Dec. 1997, pp. 2140 – 2149.
4. A. J. Tylka, J. H. Adams, P. R. Boberg, and others, “CREME96: A Revision of the Cosmic Ray Effects
on Micro-Electronics Code”, Trans. on Nucl. Sci, 44(6), Dec. 1997, pp. 2150 – 2160.
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