nd Electromagnetic Technologies Department
Sandia National Laboratories
P.O. Box 5800, M.S. 1152
Albuquerque, New Mexico 87185-1152


Abstract

Described below are major electromagnetic test facilities
at Sandia National Laboratories; each has undergone recent
upgrades. This paper will discuss each facility, their uses, and
upgrades pertaining to the facilities performance and diagnostic
capabilities. The facilities discussed here are the Sandia Lightning
Simulator, the Electromagnetic Environments Simulator, the Mode-
Stirred Chamber, and Anechoic Chamber. Sandias expertise in
electromagnetics also extends to theoretical analysis and modeling,
which can be done in conjunction with tests or experiments.


Keywords

testing, facilities, lightning, mode-stirred chambers,
anechoic chambers, TEM cells


I. INTRODUCTION
Sandia National Laboratories maintains a strong core
competency in electromagnetic environments through a
combination of experimental facilities, theoretical analysis,
and computer-based modeling and simulation. A broad
variety of problems can be addressed through testing,
analysis, or modeling, or any combination of the three. The
modeling capabilities will be briefly discussed; however, the
main focus of this paper is the major experimental facilities,
their uses, recent upgrades, and diagnostic capabilities.
II. SANDIA LIGHTNING SIMULATOR
The Sandia Lightning Simulator (SLS) allows equipment
under test to be subjected to simulated lightning currents up
to extremely severe levels. In reality, a lightning flash can
consist of multiple lightning strokes. The SLS can be
configured to produce either one or two simulated strokes,
with or without continuing current. It can deliver a maximum
peak current of 200 kA for a single stroke, 100 kA for a
subsequent stroke, and several hundred Amperes of
continuing current for hundreds of milliseconds. The
performance characteristics are listed in Table 1, and a typical
SLS single stroke is shown in Figure 1.
Test environments include direct-attachment lightning,
(where the simulator is connected to or arcs to the test
object), burn-through (which incorporates continuing
current), and nearby magnetic fields due to the strokes. The
SLS can be used to certify or evaluate hardware or to perform
research. Historically, it has been mostly used for safety
qualification testing of nuclear weapon components and
weapon systems. However, it has also been used for basic
research such as burn-through studies of different materials
[1].
A picture of the main components of the SLS is shown in
Figure 2. The simulated lightning strokes are generated by
high-voltage Marx banks (up to 1.6 MV) that are housed in
two large oil tanks for high-voltage insulation. The peak
current can be varied depending on the charge voltage of the
Marx banks. Triggered crowbar switches in each tank are
used for pulse shaping and ultraviolet lasers trigger the
crowbar switches at a predetermined time. Continuing
current, when required, is delivered by a large motor-
generator set.

Table 1. Performance Characteristics of the Sandia Lightning Simulator
Peak current
200 kA, max (single-
stroke)
Current rate of rise
200 kA/us, max
Pulse width (@50% level) 50 to 500 us (dependent
on load impedance)
Number of pulses
1 or 2
Interval between pulses
variable
Continuing current
100s A for 100s of ms

-200
-150
-100
-50
0
50
-200
0
200
400
600
800
time (us)
C
u
rren
t
(
k
A
)

Figure 1. Typical SLS Single-Stroke Output.

A. Sandia Lightning Simulator Upgrades

Previously, a large Krypton-Fluorine ultraviolet laser was
used to fire both crowbar switches. The laser light was split
and routed to each tank with mirrors. This laser was replaced
with two much smaller, less hazardous YAG lasers. The
previous laser took up a small room, required handling and
venting of toxic gas, and routing of exposed high energy laser
light. Now, each oil tank has its own laser contained in an
electromagnetically shielded box on the side of each tank,
without exposed laser light or toxic gas.


Figure 2. The Sandia Lightning Simulator.

The original low-voltage trigger system was replaced with
up-to-date trigger generators that are remotely set and
adjusted through a custom Labview program. The low-
voltage trigger system initiates the firing of the high-voltage
Marx banks, the lasers for the crowbar switches, and the
continuing current generator.

The building that houses the simulator was updated to
meet current environmental and safety regulations. Upgrades
are planned for the extensive gas system which supplies high-
voltage insulating gas to the many switches in the simulator
and for automating the high-voltage control console. The
high-voltage control console sets and monitors the gas system
pressures, the high voltage power and trigger supplies, the
continuing current generator operating parameters, and
interfaces to building safety interlocks. Future upgrades
include replacing the continuing current generator and
installing an electromagnetically shielded video system to
monitor test objects during testing.

B. Sandia Lightning Simulator Diagnostic Capabilities

The data acquisition system was also modernized to
include Tektronix TDS 7054 oscilloscopes that have multi-
frame capability for the double-pulse mode and a custom
Labview program to set the scopes and retrieve data. Three
oscilloscopes are dedicated to the simulator diagnostics, three
are dedicated for customer use, and one oscilloscope is set
aside as a spare for either use.

Simulator diagnostics include current and voltage
measurements taken for each shot, which are sent back to a
screen room via shielded coaxial cables. Three current
viewing resistors in line with the simulators return path
measure the total current for each shot. A current viewing
resistor is also used to measure the current inside each oil
tank. The high-voltage trigger generator signals are
monitored with a combination of current transformers and
current viewing resistors. The crowbar voltage is measured
with a resistive divider, and the low-voltage trigger signal to
the crowbar switch lasers is monitored. It is important to
monitor these signals. The timing between the peak Marx
bank currents and the triggering of the crowbar switches is
critical to achieving the desired peak current and protecting
the high voltage components from damage due to potential
large oscillations in the current pulse.

To minimize coupling from the electromagnetic noise
generated during a shot, test object diagnostics are shielded in
a metal instrumentation barrel. Their signals are fed through
a fiber optic system back to the screen room. Pictures of the
instrumentation barrel and fiber optic transmitters can be seen
in Figures 3 and 4. Typical diagnostics are current viewing
resistors and transformers, Rogowski coils for measuring
current derivatives, and voltage dividers. Other compatible
diagnostics are pressure transducers, temperature sensors, and
electric and magnetic field sensors (D-Dot and B-Dot,
respectively).


Figure 3. Instrumentation Barrel for Test Item Diagnostics.

Figure 4. Fiber Optic Transmitters inside the Instrumentation Barrel.
III.
ELECTROMAGNETIC ENVIRONMENTS
SIMULATOR
The Electromagnetic Environments Simulator (EMES) is a
large transverse electromagnetic (TEM) cell that propagates a
uniform, planar electromagnetic wave through the working
volume where test items are placed. EMES can be used for
continuous wave (CW) Electromagnetic Radiation (EMR)
and transient Electromagnetic Pulse (EMP) testing. The
electric field is vertically polarized between the center
conductor and the floor. If it is desired to illuminate test
objects at different polarizations, the test object can be
rotated. Its performance characteristics are listed in Table 2
and a picture of the whole facility is shown in Figure 5.
EMES has typically been used in the past to qualify
weapon systems in EMR and EMP environments. It can also
be used to evaluate prototype design behavior in these
environments, as well as for research. Recently, an
experiment was conducted in which a direct-drive waveform
was induced by electromagnetic fields in the working volume
and injected into test components to monitor susceptibility.

The EMR and EMP sources and data instrumentation are
housed in the control room. Only one source can be
connected at a time through a transition feed to the working
volume. The working volume is essentially a truncated, tri-
plate, rectangular coaxial transmission line that terminates
into a 50-Ohm load. It has a 50-Ohm intrinsic impedance
defined by

(
) =
+
+
=
50
]
coth(
1
2
[
4
377
d
g
d
w
Z
o
(1)

where w = 11.3 m, the width of center conductor, d= 8 m, the
separation of ground planes, and g = 4.25 m, the separation
between the edge of the center conductor and side walls.

Ideally, the longest wavelength, or the cutoff wavelength,
at which EMES can support fundamental TEM propagation
without higher order modes is approximately

m
d
c
16
2
=
= (2)

where c
is the cutoff wavelength and d is the same as above.
This corresponds to a cutoff frequency, above which higher
order modes can exist, of
MHz
c
f
c
c
19
=
= (3)
where c = 3*10
8
m/s, the speed of l