Final Report

1. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 1
Design, Construction and Implementation of a
Bradbury-Nielsen Gate for Time-of-Flight
Calculations for an Electrospray ThrusterAME 441aL - Group 9 Final Report
B. Dillon, L. Laxamana, K. Sampson, D. Torre
Abstract—Electrospray thrusters are increasing in popularity
for small satellite propulsion. Due to their low (µN) thrust,
measuring the thrust of electrospray thrusters is not easily
done with conventional thrust stands. For this reason, indirect
thrust measurements can offer a more practical solution. One
method of indirect thrust measurement is Time-of-Flight Mass
Spectrometry (TOF-MS). This method involves the use of an
electrostatic gate, called a Bradbury-Nielsen Gate (BNG) that
interrupts the ion plume of an electrospray thruster. The goal
of this study was to design, construct, and implement a cost-
effective and easily constructed Bradbury-Nielsen Gate to collect
TOF measurements of an electrospray thruster. To achieve this,
it was necessary for the BNG to effectively deflect the thruster’s
ion plume. A 50 wire BNG was constructed with 3”x3” frame
and a 2”x2” inner window. The BNG was installed in a vacuum
chamber along with an electrospray thruster and a faraday plate.
The thruster was fired and the BNG was cycled with a pulse
generator in order to periodically interrupt the ion plume and
take TOF measurements. Experimental data confirmed that the
BNG deflects the ion beam as expected: a current reduction
up to 94% was measured when the BNG was ON compared
to when OFF. However, due to several compounding issues —
thermal expansion of the BNG frame, high system noise, and a
questionably operating thruster — it was not possible to measure
reliable TOF values in this study. Future work on this study
should involve obtaining more capable experimental hardware
with higher resolution as well as re-evaluating BNG design
materials to address issues with thermal expansion and BNG
wire fatigue.
NOMENCLATURE
α Deflection angle
κ Dimensionless Ion Beam Deflection constant
d Wire spacing
dtrav Distance of travel for time of flight
Ekin Kinetic Energy of Molecules
m Propellant mass
q Charge
R Wire radius
V0 Thruster voltage
VBNG BNG Voltage
Vwire Wire voltage
BNG Bradbury-Nielsen Gate
CTE Coefficient of Thermal Expansion
DAQ Data Aquisition
TOF Time of Flight
I. INTRODUCTION
Due to their ability to modulate the direction of ion beams,
electrostatic ion gates are commonly used in electron mi-
croscopy, mobility spectrometers and mass spectrometers [1].
These experiments allow for measurements of mass spectra,
angle resolved current distributions, and ion fragmentation.
One of the most convenient forms of an ion gate is known
as a Bradbury-Nielsen Gate (BNG), which consists of a set of
interdigitated, electrically isolated wires held in a surrounding
frame. When two wire sets hold equal potentials, charged
particles flow through freely. When two wires sets have a
potential difference between them, an electrostatic field is
created that deflects the charged particles passing through
the device [2]. In this way, a BNG modulates ion beams
by applying a voltage to the wires, granting control over the
motion of charged particles. The ion beam is deflected by an
angle alpha (α), shown in Figure 1. Alpha can be calculated
using Equation 3 below.
Fig. 1: (a) Wires with no potential difference, no deflection
(b) Wires with a potential difference between them creating
an electrostatic field, ions deflected[1].
Initially proposed as electron filters, the first ion gates were
crafted by Loeb and Carvath in 1929 [3]. Seven years later,
Bradbury and Nielsen further developed the device and intro-
duced the Bradbury-Nielsen Gate. In 1989, the BNG’s first
use in TOF-MS was for precursor ion selection, as described
by Weinkauf, where only certain ions within a selected range
of mass-to-charge ratios were transmitted through the gate
[1,4,5].
Time-of-Flight data can be used in calculations of propul-
sion system thrust and specific impulse [5]. The propellant

2. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 2
used is 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-
BF4) which is comprised of differently massed constituents.
These constituents, called monomers, dimers, and trimers,
travel at varying velocities when accelerated by a thruster due
to their different masses. Therefore, if ejected from the thruster
simultaneously, these constituents will take different times to
travel a given distance [1]. A known distance and times of
flight provides ion exhaust velocities, from which thrust may
be calculated. Time of flight is mathematically described by
Equation 1 below:
tT OF = dtrav
mc
2qV
(1)
If these constituents were “released” from the BNG simul-
taneously and a current probe were set a known distance from
the BNG, a plot of collected current over time is theorized
below in Figure 2:
Fig. 2: Conceptual TOF plot.
BNGs offer a cost-effective alternative to direct thrust
measurement techniques and offer multiple advantages. BNG
testing environments require fewer constraints than thrust
stand environments, as the latter can be hypersensitive to light,
heat, wind and random environmental deviations. Additionally,
other TOF methods pose the risk of back-sputtering, reflect-
ing high-energy particles back toward thrusters, potentially
impacting and damaging them [6]. This is avoided with
BNGs because ion deflection decreases risk of back sputtering,
mitigates flow and prevents emission interferences.
In general, EP is used for spacecraft propulsion and attitude
control. The growing presence of EP in the space industry
increases the usefulness of characterizing EP thrusters via
diagnostics such as the BNG. This paper describes the con-
struction of an operational and cost-effective BNG to be used
in TOF testing. This project aimed to design, construct, and
implement a BNG to deflect a thruster’s ion plume for TOF
testing. Contrary to more complex designs, this construction
was intended to be done as accessible and affordable as
possible [1, 11].
A. BNG Frame Material
Delrin was chosen as the BNG frame material. It is
commonly used in vacuum chamber applications and has
advantageous mechanical and electrical properties. Compared
to other considered materials — Poly-Ether-Ether-Ketone
(PEEK), PTFE (Teflon), and Ultem 1000 — Delrin had
the second highest heat deflection temperature at 168.8◦
C
and sufficient dielectric strength of 20 kV/mm. Delrin was
also the most affordable material that satisfied experimental
requirements [7].
B. BNG Sizing: Wires and Frames
The fundamental equation governing BNG sizing is
VBNG =
2Ekin ln cot πR
2d tan α
πq
(2)
where R is wire radius, d is wire spacing (between wire
centers), α is deflection angle, and q is ion charge. Lastly,
the molecule’s kinetic energy is Ekin = 1
2 mv2
, where m is
molecular mass and v is molecular velocity.
Constraints were placed on the design such that Vwire ≤
450 V and transparency is over 70%, where transparency is
a measure of the “active open area” inside the BNG window.
Using Equation 2, relationships between Vwire, dwire, and
dspace were expressed in Figure 3 below:
Fig. 3: Theoretical behaviors for a 2” side length BNG
comprised of 30 AWG wire spaced 1 mm apart, located 1/4”
from a thruster operating at VT hruster = 1500 V. .
Using the relationships in Figure 3 along with Equation 2,
BNG dimensions were sized. The outer frame was chosen to
be 3” x 0.5” x 3” with an inner window of 2” x 2”. This
provided an “active area” of 4 in2
. With these dimensions,
the chosen BNG design included 50 bare copper wires (of
size 30 AWG) spaced 1 mm apart from each other. Copper
wires were chosen for their affordability and conductibility. A
Vwire value of 405 was expected to create a deflection angle
of 17.7◦
— clearing the collector plate by a factor of two
— with 75% transparency. Crucial to gate construction was
securing parallel, taut, electrically isolated wires to ensure a
symmetric electrical field.

3. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 3
C. Ion Beam Deflection Angle
When ions enter the BNG, a deflection angle occurs be-
tween positive and negative areas. This angle calculation is
given by Equation 3:
tan α = κ
Vwire
V0
(3)
where
κ =
π
2 ln cot πR
2d
(4)
This plume deflection is dependent on electric field strength
between wire sets. Wire spacing, size, and potential differences
drive this field strength, which affect the ion beam as shown
in Figure 4 below:
Fig. 4: Cross-sectional view of positive (red) and negative
(black) wires, demonstrating how the BNG’s induced electric
field driving ion deflection [8].
For the nominal VBNG of 420 V, a deflection angle of 15.4◦
was expected.However, several changes were made during the
progression of the experiment, including a new thruster voltage
of 2200 V, VBNG = 605 V, and distance between thruster and
BNG of 0.25 inches. For these parameters, a deflection angle
of 15.0◦
was expected.
II. EXPERIMENTAL TECHNIQUE
A. BNG Frame Preparations
Previous BNG manufacturing methods required microma-
chining capabilities and long build time [1, 11]. Because
micromachining at the level of thousandths of inches was not
an option for this study, these methods were deemed unviable.
In the method below, two 3-inch Delrin squares were cut from
a 1/4” thick sheet. A 2 x 2” window was machined from the
center of the larger 3-inch square. Each square serves as one
half of the BNG frame, which was “sandwiched” together with
the second half to form a complete, 1/2” thick BNG.
In order to maintain consistent spacing of wires, 50 grooves
were laser-etched into one frame half. The grooves are spaced
1 mm apart and span the window length. Each groove is 0.005
± 0.001 inches deep, and 0.003 ± 0.001 inches in width. The
etched BNG frame half will be referred to as BNG-1 and the
unetched half as BNG-2. The etched half of the BNG frame,
BNG-1 is shown in Figure 5.
Fig. 5: Delrin frame with 50 1mm spaced etches.
B. Wire Lacing Method - Combs and Stage
Physically arranging all 50 wires in the BNG is referred
to as “wire lacing.” The wire lacing was performed on a
horizontal platform called the “stage.” The stage, shown in
Figure 6b, was built to provide a structure that aids in
maintaining uniform tension and linear spacing. As shown in
Figure 6a, BNG-1 is positioned in the center of the stage. Two
symmetric 1” x 3” x 1/8” acrylic rectangles (“Combs”) were
secured on either side of BNG-1 on the inner portion of the
stage (refer to Figure 6). 50 evenly spaced 1 mm triangular
holes — spanning 2” — were cut to match BNG-1’s window
length. These holes guided the wires during lacing and held
them at 1 mm spacing. To ensure wire tension, 25 nails and
50 screws were fastened on opposite sides of the stage. Nails
were positioned in two rows, with 13 and 12 nails, respectively.
Screws were positioned in a staggered manner. This variably
tensioned system is explained further in BNG Manufacturing.

4. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 4
Fig. 6: Stage V4.0. (a) Schematic of the Stage. Crossbar
omitted for clarity. (b) Real image of the stage. Note, Comb
triangular holes are aligned with BNG-1 grooves, with a 1/8"
vertical offset, therefore shear force applied on the wires by
the combs can be ignored.
The comb profile shown in Figure 7 maintains uniform
spacing while not snapping wires under shear stress:
Fig. 7: Selected Comb design with V-grooves used to maintain
wire spacing in lacing method.
A horizontally-oriented stage (Stage V4.0) was built for the
lacing process. Using wood pieces and metal brackets, Stage
V4.0 reduced vertical wire sway and simplified the securing
process of both BNG frames.
C. BNG Manufacturing
During lacing, 25 wires of approximate length of 4.5’ ±
0.3’ wires were cut with one end secured to “tuning pegs”
(screws) on one side of the stage. The wire was then passed
through the combs, across BNG-1, and looped around a nail.
After this, the wire returned across BNG-1 to its initial side,
where the remaining free end was attached to another tuning
peg. Reference Figure 6.
This method allowed for two BNG-1 grooves to be laced
using one 4.5’ wire. Wires — each with their corresponding
comb holes and BNG-1 grooves — were manually pulled
taut and wrapped around their corresponding screws, fixing
them in place. Fine-tuning (or tightening) the screws increased
individual wire tension.
After all wires were laced, BNG-2’s interior frame surface
was roughed with coarse sandpaper. Loctite R 1CTM
Epoxi-
PatchTM
Hysol [7] was applied to the surface, after which
BNG-2 was positioned onto BNG-1 and secured with metal
fasteners. Because the Delrin frame size fluctuates as a func-
tion of temperature, it was imperative to control the frame tem-
perature during curing. Further, multiple temperature swings
(from curing temperature to vacuum chamber temperature)
could cause wires to fatigue and lose tension. A correlation
between the frame’s thermal expansion and temperature is
demonstrated below in Figure 8:
Fig. 8: Temperature versus thermal expansion of the frame.
Ice packs were placed in contact with the curing BNG to
decrease frame temperature to 16.1◦
± 0.5◦
C, as shown below
in Figure 9:
Thermal expansion of the frame with its corresponding
effect on wires and force on wires are all discussed in section
’C. Thermal Expansion of Frame’ below.
After the epoxy had cured, wires were cut from the stage
with approximately 4” of loose ends. These ends were soldered
to a common contact, with wires alternating between positive
and negative contacts. Copper tape was applied to the thruster-
facing side of the BNG to prevent charge build-up in vacuum.
Figure 10 below depicts (a) wires, (b) an isometric view, (c)
and implementation of the BNG:
In order to take non-intrusive measurements of the wire
spacing, a frontal photo of the BNG was taken. Then, a
reference length was taken and measured in pixels in order to
get pixel to unit length conversion. From there, the distance
between the wires was measured in pixels and consequently
converted to unit lengths.
D. Experimental Setup
To cycle the BNG voltage, a triggering function was sent to
a DEI Pulse Generator from a function generator. The function
generator output a 5 V square wave at 10 kHz, on a 50%
duty cycle. This triggers the DEI pulse generator at the same

5. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 5
Fig. 9: Stage V4.0 with ice packs in contact with BNG frame.
Fig. 10: (a) Zoom-in wire layout (b) Copper taped BNG (c)
Final BNG aligned with thruster inside the vacuum chamber.
frequency, supplying high voltage to the BNG at 10 kHz. To
record the current signal from the faraday plate, the signal
was sent through a Stanford Research Systems SR570 Current
Preamplifier. This preamplifier was used to convert the current
readings across our faraday sensor into voltage. The current
was amplified with a gain of 20 nA/V. The voltage signal from
the preamplifier was recorded using the digital oscilloscope
function of an NI VirtualBench 8012. Data collection was
automated with LabView code.
Fig. 11: Schematic demonstrating experimental setup inside
vacuum chamber.
E. Data Collection Method
Before data collection, all experimental components were
installed in the vacuum chamber and it was sealed. Initially,
a roughing pump was used to bring the chamber from atmo-
spheric pressure down to 20 mTorr. A cryogenic pump was
then used to bring the chamber pressure down to 1e-6 Torr.
For the purposes of this study, this pressure was considered
an effective vacuum.
Faraday plate baseline tests were conducted. In these tests
the thruster was first OFF and then turned ON. The faraday
plate current was recorded in LabView and is shown in
Figure 16. BNG cycling tests were also conducted, where the
BNG was cycled ON and OFF from the DEI Pulse Generator
as outlined in ’D. Experimental Setup’. In these tests, the
thruster is ON while the BNG modulates. It is expected to
see a cycle in current on the faraday plate. As before, the
faraday plate current was recorded in LabView and is shown
in Figure 17. From these tests, it is expected that TOF values
can be measured.
Additional data was collected with a faraday cup on an XYZ
stepper motor traverse within the vacuum chamber. Sweeps
across the thruster plume were conducted while the thruster
was ON, first with the BNG OFF and again with the BNG
ON. This data was used to map and calculate the ion plume
deflection angle. This is shown in Figure 16 . These sweeps
were conducted at 2.94 inches from the BNG.
In all tests, the faraday plate was covered by a cardboard
baffle, reducing the active impact area of the plate. This was
done to reduce noise registered on the faraday plate. The
baffle optimized data collection to produce clearer data. The
baffle was covered in conductive copper and aluminum tape
and grounded, to avoid charge build up. If the baffle was
not grounded, the dielectric build up could potentially retard
incoming ions [6]. This is shown in Figure 12:

6. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 6
Fig. 12: Experimental setup with grounded baffle fastened onto
the faraday plate.
III. RESULTS
A. Thruster Operations
To observe thruster operation, three baseline thruster read-
ings were taken to test stability of the device:
Fig. 13: VBlue = 2242 V, VRed = 2200 V, VY ellow = 2244 V.
As shown in Figure 13, the thruster behaves as expected —
the signal plummets when powered off and increases abruptly
when powered on. However, thruster noise should be noted
when powered on. Variations during “nominal” performance
exist and are further discussed in Section 4.4.
B. Baseline Faraday Plate Plot for BNG Off
With the thruster continuously running, collector plate base-
line data was taken while manually powering the BNG on and
off at different times, as shown below in Figure 14:
Fig. 14: With a pre-amp setting of 20 nA/V, the BNG was
powered on at roughly five seconds and powered off at roughly
13 seconds.
As expected, signal abruptly decreased when the BNG was
powered on and increased when the BNG was turned off.
C. Signal Reduction as a Function of VBNG
To illustrate the effect of VBNG on signal response, nor-
malized current readings were taken and are illustrated below
in Figure 15:
Fig. 15: Normalized current responses from manually power-
ing the BNG on at t = 10 seconds.
Furthermore, signal reduction percentages were calculated
and shown in Table I:

7. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 7
TABLE I: Percent signal reduction based on BNG voltage.
V % Reduction
0 0
420 36.8
530 77.2
605 94.0
Unsurprisingly, larger VBNG values correspond to less
captured current, which is due to larger deflection angles.
D. Probe Sweep Results
A theoretical beam deflection angle was calculated at 15.0
±0.2◦
. Using the XYZ stepper motor system, the Faraday
probe was horizontally scanned twice through the ion plume,
and current readings were averaged across both sweeps. With
the thruster centered at 2.125”, current readings over the scan
area are presented in Figure 16:
Fig. 16: Averaged faraday probe scan taken 2.94 ± 0.01” from
the BNG, where VT hruster = 2422 V.
While Figure 16 shows a visible parting of current, the
experimentally calculated deflection angle was just over half
of the theoretical deflection angle, at 8.8 ± 0.2◦
.
E. Theorized Successful TOF
Using Equation 1, theoretical TOF values were calculated
and recorded in Table II for various VT values:
TABLE II: Expected TOF Values for EMI-BF4 Constituents.
V0 1500 [V] 2090 [V] 2244 [V]
Polarity + - + - + -
Monomers* 1.5171 1.3431 1.2852 1.1378 1.2403 1.0981
Dimers* 2.5312 2.4309 2.1444 2.0594 2.0695 1.9875
Trimers* 3.2423 3.1646 2.7468 2.6810 2.6509 2.5874
TOF units are E-5 s.
Theoretical TOF values for VT hruster = 2090 V were
applied to a BNG cycling test, where a positive faraday plate
signal corresponds to the BNG powered on. As the signal
response trends downward, more ions are collected by the
faraday plate. This is due to the signal’s negative polarity,
as shown in Figure 17:
Fig. 17: TOF test results at a cycling frequency of 10 kHz.
IV. DISCUSSION
A. Ion Beam Deflection Angle
Although it is difficult to say with certainty, the 6o
± 2o
error between theoretical and experimental results is likely due
to the thruster’s inconsistent ion flow. Deflection angle equa-
tions assume orthogonal impact, however since the thruster
has a half angle of 36◦
, this assumption was invalid. For that
reason, recorded value of 8.8o
± 0.2o
differs considerably from
the theoretical value of 15.0o
± 0.2o
.
B. Preamplifier Analysis
During initial setup of our TOF data collection system, the
preamplifier was unintentionally exposed to 15 mA of current;
the maximum input current is listed as 10mA. Following
this incident it was discovered that one of the two onboard
op-amps had been damaged and was no longer operational.
For this reason the preamplifier was only able to be used
in gain configurations that used the undamaged op-amp. For
this experiment, the only setting that was available that was
reasonably viable for data collection was a gain setting of 20
nA/V. At this gain setting, the preamplifier output ranged from
0-7 V. At this range our 8-bit VirtualBench was limited to a
less desirable resolution, as can be seen in Figure 17. A lower
gain setting, say 100 nA/V, would have produced a smaller
Vrange and allowed for a higher resolution. Although there
was experimental equipment available with a finer resolution
than the VirtualBench, such as a 16-bit NI-DAQ 6211, this
device did not provide a high enough sampling rate. The NI-
DAQ 6211 is limited to 250 kS/s where the VirtualBench
provides up to 5 MS/s. Due to the high frequency nature
of BNG cycling, the higher sampling frequency is necessary.
Another issue stemming from the preamplifier was the gain
mode setting. There are three gain modes: "Low Noise", "Low
Drift", and "High Bandwidth”, and due to the damaged op-
amp, only the low drift gain mode was available for use. The
low drift setting is a low bandwidth setting that is less capable
of sensing fast changes in input. This is a potential cause for
error due to the high frequency nature of this study.

8. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 8
C. Thermal Expansion of Frame
Although Delrin has beneficial properties with respect to
out-gassing and dielectric strength, its relatively high coeffi-
cient of thermal expansion (CTE) proved to be a significant
issue with BNG fabrication, this is demonstrated below in
Figure 18:
Fig. 18: CTE comparison plot of 3 different engineering
plastics.
Due to budget constraints, materials with lower CTE values
could not be obtained. PEEK is a possible substitute for Delrin,
and has a CTE of 2.6E-5. This may avoid thermal expansion
issues (i.e stretching BNG wires past their yield point).
For a BNG epoxied at room temperature then installed in a
cooler vacuum temperature, the frame was “cooled” by 3.8o
C
± 0.5o
C and underwent thermal contraction. This caused the
frame to shrink and wires to slack and arc. The total wire
length of the room temperature BNG was 50.7 ± 0.2 mm
with an average strain of 2.78e-3%.
For the BNG epoxied at a cooler temperature then in-
troduced to a warmer vacuum temperature, the frame was
“heated” by 5.5o
± 0.5o
C and underwent thermal expansion.
In doing so, the frame pulls on the wires and optimizes tension
without surpassing yield strength of 1.8e-4 ± 0.1 MPa. The
total wire length of the chilled BNG was 50.8 ± 0.2 mm with
an average strain of 1.99e-04%.
Delrin’s linear thermal expansion values for room temper-
ature and ice-pack curing temperature are tabulated below,
respectively:
TABLE III: Thermal Expansion Values of the BNG frame and
wires.
Initial T [◦C] Final T [◦C] Frame Wire
(Curing) (Vacuum) Expansion [mm] Expansion [mm]
25.4 ± 0.5 21.6 ± 0.5 -0.231 ± 0.003 -0.141 ± 0.002
16.1 ± 0.5 21.6 ± 0.5 0.334 ± 0.003 0.010 ± 0.002
Figure 19 stress-strain curve undergone by the wires at
chilled (ice) curing temperature, with an elastic limit of 1954.2
MPa and ultimate stress (U) of 2188.7 MPa:
Fig. 19: Stress is proportional to strain, obeying Hooke’s Law.
Here, E is the elastic limit, and U is the ultimate Stress point,
and B is the breaking point [10].
D. Time of Flight
Theoretical TOF values match with the results obtained
in Figure 17, but the accuracy of this data is dubious. The
lack of consistent and reliable TOF values is likely due to
a signal reduction rate of only 77.2% from the 530 V BNG
potential in Figure 15. Because there has yet to be a nearly
100% signal reduction rate, it is unlikely that the faraday plate
(and subsequently the preamplifier) captured such minute,
nanoAmpere changes in signal magnitude. For this reason,
it is more likely that Figure 17 is signal noise rather than
discernable TOF data of the propellant constituents.
Possible explanations for this lack of complete thruster
current reduction, and thus lack of trustworthy TOF tests,
include the following. As the thruster continues to fire in the
vacuum chamber, ambient plasma presence increases, which
may affect faraday plate readings. As shown by the “nominal”
thruster response in Figure 13, there are signal variations on
the order of tenths of volts. Lack of confident TOF tests could
also be attributed to inconsistent thruster responses.
V. CONCLUSION
The goal of this study was to design, construct, and imple-
ment a cost-effective and easily constructed Bradbury-Nielsen
Gate to collect TOF measurements of an electrospray thruster.
To achieve that, it was necessary for the BNG to effectively
deflect the thruster’s ion plume. The BNG constructed for
this study did effectively deflect the ion beam Figure 15.
However, the recorded deflection angle did not meet project
requirements. As discussed in section 4.1, this is likely due to
the falsely assumed orthogonal impact between the ion plume
and the BNG active area.
Lack of appropriate deflection angle compromised validity
and reliability of TOF tests. This failure is not suspected
to be a result of poor bng construction, but rather a result
of several issues in the experimental and data collection
setup. These issues may include fundamental issues between
the faraday plate, preamplifier, Virtual Bench, and LabVIEW
code. Although this was scrutinized and no issues were found,
it remains a possible cause for error.

9. AME 441AL SENIOR PROJECTS LAB. FINAL REPORT, DECEMBER 2019 9
Although the main objective of this study was not achieved,
several useful lessons were learned. The BNG constructed
did meet the project goals of having taut, parallel lines with
uniform 1 mm spacing as shown in Figure 10 and calculated
in Section 1.2. Baffling the faraday plate significantly reduced
system noise, which suggests that a detailed investigation is
required in the experimental set up to further reduce data
uncertainty.
A. Future Work
Future work involves replacing the BNG frame with a
similar material of lower CTE.
In the initial proposal of this project, a scaled 6” x 6”
BNG was suggested. However, due to the myriad problems
described — thermal expansion of the frame, wire deforma-
tion, and the current wire lacing method — the scaled BNG
was not pursued.
To reduce noise of the faraday plate and minimize the
required deflection angle, a more constricting, secured baffle
may be attached to the existing faraday plate.
A more reliable and consistent thruster would eliminate
variants in current, minimize uncertainty and provide refined
data.
In sum, the following must be pursued: a more reliable
experimental set up, fully functioning preamplifier, and a data
acquisition system with higher resolution and sampling rate.
With all these things, BNG cycling tests for TOF can be
repeated, and these changes are expected to enhance reliability
for successfully measuring TOF values.
ACKNOWLEDGMENT
This research was conducted using the facilities of the
USC Laboratory for Advanced Plasma Dynamics (LAPD).
Equipment was supplied in part from funding provided by
the Air Force Research Laboratory (AFRL).
We thank Dr.(s) Matthew Gilpin, Charles Radovich, David
Petty , Rodney Yates, Jeffrey Vargas, William Colvin and the
entire 441a Staff for their assistance with this project.
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